44 The density of a material varies with temperature and pressure. This variation is typically small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object and thus increases its density. Increasing the temperature of a substance (with a few exceptions) decreases its density by increasing its volume. In most materials, heating the bottom of a fluid results in convection of the heat from the bottom to the top, due to the decrease in the density of the heated fluid. This causes it to rise relative to more dense unheated material. The reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density; rather it increases its mass. 3.1.1 Measurement of density Homogeneous materials The density at all points of a homogeneous object equals its total mass divided by its total volume. The mass is normally measured with a scale or balance; the volume may be measured directly (from the geometry of the object) or by the displacement of a fluid. To determine the density of a liquid or a gas, a hydrometer, a dasymeter or a Coriolis flow meter may be used, respectively. Similarly, hydrostatic weighing uses the displacement of water due to a submerged object to determine the density of the object. Heterogeneous materials If the body is not homogeneous, then its density varies between different regions of the object. In that case the density around any given location is determined by calculating the density of a small volume around that location. In the limit of an infinitesimal volume the density of an inhomogeneous object at a point becomes: ρ( ) = dm/dV, where dV is an elementary volume at position r. The mass of the body then can be expressed as Non-compact materials In practice, bulk materials such as sugar, sand, or snow contain voids. Many materials exist in nature as flakes, pellets, or granules. Voids are regions which contain something other than the considered material. Commonly the void is air, but it could also be vacuum, liquid, solid, or a different gas or gaseous mixture.
45 The bulk volume of a material—inclusive of the void fraction—is often obtained by a simple measurement (e.g. with a calibrated measuring cup) or geometrically from known dimensions. Mass divided by bulk volume determines bulk density. This is not the same thing as volumetric mass density. To determine volumetric mass density, one must first discount the volume of the void fraction. Sometimes this can be determined by geometrical reasoning. For the close-packing of equal spheres the non-void fraction can be at most about 74%. It can also be determined empirically. Some bulk materials, however, such as sand, have a variable void fraction which depends on how the material is agitated or poured. It might be loose or compact, with more or less air space depending on handling. In practice, the void fraction is not necessarily air, or even gaseous. In the case of sand, it could be water, which can be advantageous for measurement as the void fraction for sand saturated in water— once any air bubbles are thoroughly driven out—is potentially more consistent than dry sand measured with an air void. In the case of non-compact materials, one must also take care in determining the mass of the material sample. If the material is under pressure (commonly ambient air pressure at the earth's surface) the determination of mass from a measured sample weight might need to account for buoyancy effects due to the density of the void constituent, depending on how the measurement was conducted. In the case of dry sand, sand is so much denser than air that the buoyancy effect is commonly neglected (less than one part in one thousand). Mass change upon displacing one void material with another while maintaining constant volume can be used to estimate the void fraction, if the difference in density of the two voids materials is reliably known. 3.2 Relative Density Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity usually means relative density with respect to water. The term "relative density" is often preferred in modern scientific usage. If a substance's relative density is less than one then it is less dense than the reference; if greater than 1 then it is denser than the reference. If the relative density is exactly 1 then the densities are equal;
46 that is, equal volumes of the two substances have the same mass. If the reference material is water then a substance with a relative density (or specific gravity) less than 1 will float in water. For example, an ice cube, with a relative density of about 0.91, will float. A substance with a relative density greater than 1 will sink. Temperature and pressure must be specified for both the sample and the reference. Pressure is nearly always 1 atm equal to 101.325 kPa. Where it is not, it is more usual to specify the density directly. Temperatures for both sample and reference vary from industry to industry. In British brewing practice the specific gravity as specified above is multiplied by 1000. [3] Specific gravity is commonly used in industry as a simple means of obtaining information about the concentration of solutions of various materials such as brines, sugar solutions (syrups, juices, honeys, brewers wort, must, etc.) and acids. 3.2.1 Basic formulas Relative density (RD) or specific gravity (SG) is a dimensionless quantity, as it is the ratio of either densities or weights where RD is relative density, ρsubstance is the density of the substance being measured, and ρreference is the density of the reference. (By convention ρ, the Greek letter rho, denotes density.) The reference material can be indicated using subscripts: RDsubstance/reference, which means "the relative density of substance with respect to reference". If the reference is not explicitly stated then it is normally assumed to be water at 4 °C (or, more precisely, 3.98 °C, which is the temperature at which water reaches its maximum density). In SI units, the density of water is (approximately) 1000 kg/m 3 or 1 g/cm 3 , which makes relative density calculations particularly convenient: the density of the object only needs to be divided by 1000 or 1, depending on the units. The relative density of gases is often measured with respect to dry air at a temperature of 20 °C and a pressure of 101.325 kPa absolute, which has a density of 1.205 kg/m 3 . Relative density with respect to air can be obtained by
47 Where M is the molar mass and the approximately equal sign is used because equality pertains only if 1 mol of the gas and 1 mol of air occupy the same volume at a given temperature and pressure i.e. they are both Ideal gases. Ideal behaviour is usually only seen at very low pressure. For example, one mol of an ideal gas occupies 22.414 L at 0 °C and 1 atmosphere whereas carbon dioxide has a molar volume of 22.259 L under those same conditions. 3.2.2 How to Test Plastic Properties Specific Gravity/ Relative Density is a strong element in the price factor and thus has great importance. Beyond the price/volume relationship, however, specific gravity is used in production control, both in raw material production and molding and extrusion. Polyethylenes, for example, may have density variation, depending upon the degree of "packing" during molding, or the rate of quench during extrusion. Although specific gravity and density are frequently used interchangeably, there is a very slight difference in their meaning. Specific gravity is the ratio of the weight of a given volume of material at 73.4 °F (23 °C) to that of an equal volume of water at the same temperature. It is properly expressed as Specific Gravity, 23/23 °C. Density is the weight per unit volume of material at 23 °C and is expressed as D23C, g/cm3. The discrepancy enters from the fact that water at 23 °C has a density slightly less than one. ASTM D-792. 3.3 Mould Shrinkage What is the Molding Shrinkage Phenomenon? Figure 3.1 Shrinkage Phenomenon
48 In the injection molding of thermoplastic plastics, it is possible to obtain a molded product with the desired dimensions using the mold shrinkage phenomenon. Mold shrinkage is the phenomenon where the volume of the molten plastic filled inside the cavity of a mold is shrinking at the time as being cooled and solidifying. The extent of this shrinkage is called the "molding shrinkage factor", and if this molding shrinkage factor is known accurately both scientifically and by experience, by preparing the mold making the dimensions of the cavity a little larger by the amount of shrinkage, it is possible to form the molded item by so that it has the intended dimensions. The value of the molding shrinkage factor is generally a number in the range of about 2/1000 to 20/1000 (about 0.2 to 2%). If the molding shrinkage factor is expressed by the symbol α (alpha), it can be defined by the following equation 1 α=(L0−L)／L0 ... (Eq.1) Where, L0: the cavity dimensions (mm) L: Dimensions (in mm) of the molded product at room temperature (usually 20ºC). 3.3.1 Further the molding shrinkage factor is affected by the following factors. 1. Type of molding material The range of the basic shrinkage factor is determined by the type of plastic material being used. However, there will be fine differences depending on the material manufacturer and the grade of the material. 2. Cavity surface temperature The molding shrinkage factor varies depending on the cavity surface temperature during injection molding. In general, the shrinkage factor tends to be large when the temperature is high. 3. Maintained pressure × pressure maintenance time The molding shrinkage factor varies depending on the magnitude of the pressure maintained after plastic injection and the time of maintaining that pressure. In general, there is trend in the shrinkage
49 factor becoming smaller when the maintained pressure is high and the pressure maintenance time is long. 4. Wall thickness of the molded item The shrinkage factor also varies depending on the wall thickness of the molded item. There is a trend in the shrinkage becoming larger as the wall thickness becomes larger. 5. Gate shape The shrinkage factor varies depending on the gate shape and the gate size. In general, there is a trend in the shrinkage becoming smaller as the cross-sectional area of the gate becomes larger. There is also a trend in the shrinkage becoming smaller in the case of a side gate rather than in the case of a pinpoint gate or a submarine gate. 6. Presence or absence of additive materials to the molding material It is very common that there is a large difference in the shrinkage factor between natural materials and materials having glass fibers. There is a trend in the shrinkage factor being smaller in the case of materials with glass fibers. In actuality, the molding shrinkage factor for mold design is determined by comprehensively investigating the above conditions. 3.4 Tensile Creep What is a Creep Test? Creep is high temperature progressive deformation at constant stress. "High temperature" is a relative term dependent upon the materials involved. Creep rates are used in evaluating materials for boilers, gas turbines, jet engines, ovens, or any application that involves high temperatures under load. Understanding high temperature behavior of metals is useful in designing failure resistant systems. A creep test involves a tensile specimen under a constant load maintained at a constant temperature. Measurements of strain are then recorded over a period of time. Creep occurs in three stages: Primary, or Stage I; Secondary, or Stage II: and Tertiary, or Stage III.
50 Stage I, or Primary creep occurs at the beginning of the tests, and creep is mostly transiently, not at a steady rate. Resistance to creep increases until Stage II is reached. In Stage II, or Secondary creep, The rate of creep becomes roughly steady. This stage is often referred to as steady state creep. In Stage III, or tertiary creep, the creep rate begins to accelerate as the cross sectional area of the specimen decreases due to necking or internal voiding decreases the effective area of the specimen. If stage III is allowed to proceed, fracture will occur. The creep test is usually employed to determine the minimum creep rate in Stage II. Engineers need to account for this expected deformation when designing systems. Like the Creep Test, Stress Rupture Testing involves a tensile specimen under a constant load at a constant temperature. Stress rupture testing is like creep testing aside from the stresses are being higher than those utilized within a creep testing. Stress rupture tests are utilized to find out the time it takes for failure so stress rupture testing is always continued until failure of the material occurs. Data is plotted similar to the graph above. A straight line or best fit bend is normally obtained at every temperature of interest. The Stress Rupture test is used to determine the time to failure and elongation.
51 CHAPTER 4 THERMAL PROPERTIES This topic provides an understanding to thermal properties and testing of plastic materials such as Thermal Conductivity, Deflection Temperature, Ablative Plastics, Flammability, Melt Index, Glass Transition Temperature and Softening Point. The thermal properties of plastics can be characterized in particular by their service temperatures and their thermal dimensional stability, and by the glass transition temperature. In addition, the coefficient of thermal expansion and coefficient of linear thermal expansion also have to be noted for the application of plastics. 4.1 Thermal conductivity The thermal conductivity is the rate of heat transfer through a material in steady state. It is not easily measured, especially for materials with low conductivity but reliable data is readily available for most common materials. In heat transfer, the thermal conductivity of a substance, k, is an intensive property that indicates its ability to conduct heat. Thermal conductivity is often measured with laser flash analysis. Alternative measurement are also established. Mixtures may have variable thermal conductivities due to composition. 4.2 Deflection Temperature The heat deflection temperature or heat distortion temperature (HDT, HDTUL, or DTUL) is the temperature at which a polymer or plastic sample deforms under a specified load. This property of a given plastic material is applied in many aspects of product design, engineering, and manufacture of products using thermoplastic components.
52 The deflection temperature is a measure of a polymer's ability to bear a given load at elevated temperatures. The deflection temperature is also known as the 'deflection temperature under load' (DTUL), 'heat deflection temperature', or 'heat distortion temperature' (HDT). The two common loads used are 0.46 MPa (66 psi) and 1.8 MPa (264 psi), although tests performed at higher loads such as 5.0 MPa (725 psi) or 8.0 MPa (1160 psi) are occasionally encountered. The common ASTM test is ASTM D 648 while the analogous ISO test is ISO 75. The test using a 1.8 MPa load is performed under ISO 75 Method A while the test using a 0.46 MPa load is performed under ISO 75 Method B. The figure below, from Quadrant Engineering Plastic Products, shows the test geometry. 4.2.1 How to Test Plastic Properties Deflection Temperature shows the temperature at which an arbitrary amount of deflection occurs under established loads. It is not intended to be a direct guide to high temperature limits for specific applications. It may be useful in comparing the relative behavior of various materials in these test conditions, but it is primarily useful for control and development purposes. A specimen is placed on supports 4 inches apart and a load of 66 or 264 psi is placed on the center. The temperature in the chamber is raised at the rate of 2 + 0.2 °C per minute. The temperature at which the bar has deflected 0.010 inch is reported as "deflection temperature at 66 (or 264) psi fiber stress." ASTM D-648. ASTMD648: The deflection temperature is the temperature at which a test bar, loaded to the specified bending stress, deflects by 0.010 inch (0.25 mm).
53 4.3 Ablative plastics An ablative plastics is one that absorbs heat and generally protects other parts from the effects of the heat. The ablative plastic will absorb heat while it decomposes. The decomposition process is termed pyrolysis. Ablation takes place in the near surface layer exposed to the heat. The degraded outer surfaces will break away when decomposed and exposed a new surface to the heat. Phenolic are good ablative plastics in that, when exposed briefly to very high temperatures, they undergo rapid decomposition to gases and form a porous char, thereby dissipating heat and leaving a protective thermal barrier on the substrate. This sacrificial loss of material accompanied by the transfer of energy is known as ablation. In addition to providing for heat absorption and heat dissipation per unit mass expended, ablative materials are used because they provide an automatic control of surface temperatures by selfregulating ablative degradation: excellent thermal insulation; tailored performance by varying the individual material components and composition of the ablative system; design simplicity and ease of fabrication and light weight and low cost materials. An example of an application for an ablative plastic is the outer skin of space craft where the plastic is used as a heat shield. Ablative polymers are also often used as fire protection in cable runs, electrical equipment, fire barriers in buildings etc. some ablative polymers are known as fire stop material. 4.4 Flammability Flammability is the ability of a substance to burn or ignite, causing fire or combustion. The degree of difficulty required to cause the combustion of a substance is quantified through fire testing. Internationally, a variety of test protocols exist to quantify flammability. The ratings achieved are used in building codes, insurance requirements, fire codes and other regulations governing the use of building materials as well as the storage and handling of highly flammable substances inside and outside of structures and in surface and air transportation. For instance, changing an occupancy by altering the flammability of the contents requires the owner of a building to apply for a building permit to make sure that the overall fire protection design basis of the facility can take the change into account.
54 4.4.1 How to Test Plastic Properties Flammability for plastics thicker than 0.050 in. if the specimen does not ignite, it is classed non-burning by this test. If the specimen continues to burn, it is timed until it stops or a 4 in. mark is reached. A specimen which burns to the 4 in. mark is classed as burning by this test and the rate is equal to (180/time) in. per min. If the specimen does not continue burning to the 4 in. mark, it is classed as selfextinguishing and the length of the burned portion is reported as the extent of burning. The specimen is clamped at one end on a ring stand so the longitudinal axis is horizontal and the transverse axis is inclined 45° to horizontal. A piece of 20-mesh Bunsen burner gauze is clamped horizontally 3/8 inch below the specimen. A Bunsen burner, placed so the flame contacts the end of the specimen, is held 30 seconds and then removed. If the specimen does not ignite, the burner is returned for another 30-second attempt. The burning is measured along the lower edge of the specimen. ASTM D-635. 4.5 Melt Index The melt flow index (MFI) is a measure of the ease of flow of the melt of a thermoplastic polymer. It is defined as the mass of polymer, in grams, flowing in ten minutes through a capillary of a specific diameter and length by a pressure applied via prescribed alternative gravimetric weights for alternative prescribed temperatures. The method is described in the similar standards ASTM D1238 and ISO 1133. Melt flow rate is an indirect measure of molecular weight, with high melt flow rate corresponding to low molecular weight. At the same time, melt flow rate is a measure of the ability of the material's melt to flow under pressure. Melt flow rate is inversely proportional to viscosity of the melt at the conditions of the test, though it should be borne in mind that the viscosity for any such material depends on the applied force. Ratios between two melt flow rate values for one material at different gravimetric weights are often used as a measure for the broadness of the molecular weight distribution. Melt flow rate is very commonly used for polyolefin, polyethylene being measured at 190 °C and polypropylene at 230 °C. The plastics engineer should choose a material with a melt index high enough that the molten polymer can be easily formed into the article intended, but low enough that the mechanical strength of the final article will be sufficient for its use.
55 4.6 Glass Transition Temperature and Softening Point. The glass–liquid transition (or glass transition for short) is the reversible transition in amorphous materials (or in amorphous regions within semi crystalline materials) from a hard and relatively brittle state into a molten or rubber-like state. An amorphous solid that exhibits a glass transition is called a glass. Super cooling a viscous liquid into the glass state is called vitrification, from the Latin vitreum, "glass" via French vitrifier. Despite the massive change in the physical properties of a material through its glass transition, the transition is not itself a phase transition of any kind; rather it is a laboratory phenomenon extending over a range of temperature and defined by one of several conventions. Such conventions include a constant cooling rate (20 K/min) and a viscosity threshold of 10 12 Pa, among others. Upon cooling or heating through this glass-transition range, the material also exhibits a smooth step in the thermal expansion coefficient and in the specific heat, with the location of these effects again being dependent on the history of the material. However, the question of whether some phase transition underlies the glass transition is a matter of continuing research. The glass-transition temperature Tg is always lower than the melting temperature, Tm, of the crystalline state of the material, if one exists. The softening point is the temperature at which a material softens beyond some arbitrary softness. It can be determined, for example, by the Vicat method (ASTM-D1525 or ISO 306), Heat Deflection Test (ASTM-D648) or a ring and ball method (ISO 4625 or ASTM E28-67/E28-99 or ASTM D36 or ASTM D6493 - 11). 4.6.1 How to Test Plastic Properties Vicat Softening Point a good way to compare the heat softening characteristics of polyethylenes. Also, it may be used with other thermoplastics.The apparatus for testing Vicat softening point consists of a temperature regulated oil bath with a flat ended needle penetrator so mounted as to register degree of penetration on a gauge. A specimen is placed with the needle resting on it. The temperature of the bath (preheated to about 50 °C lower than anticipated Vicat softening point) is raised at the rate of 50 °C/hr. or 120 °C/hr. The temperature at which the needle penetrates 1 mm. is the Vicat Softening Point. ASTM D-1525.
56 Figure 4.1 Temperature Transition of Plastics 4.7 Thermal Diffusivity The thermal diffusivity is a measure of the transient heat flow through a material. In heat transfer analysis, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It measures the ability of a material to conduct thermal energy relative to its ability to store thermal energy. It has the SI unit of m²/s. Thermal diffusivity is usually denoted α but a, κ, K, and D are also used. The formula is: where is thermal conductivity (W/(m·K)) is density (kg/m³) is specific heat capacity (J/(kg·K)) Together, can be considered the volumetric heat capacity (J/(m³·K)).
57 As seen in the heat equation. , Thermal diffusivity is the ratio of the time derivative of temperature to its curvature, quantifying the rate at which temperature concavity is "smoothed out". In a sense, thermal diffusivity is the measure of thermal inertia. In a substance with high thermal diffusivity, heat moves rapidly through it because the substance conducts heat quickly relative to its volumetric heat capacity or 'thermal bulk'. Thermal diffusivity is often measured with the flash method. It involves heating a strip or cylindrical sample with a short energy pulse at one end and analyzing the temperature change (reduction in amplitude and phase shift of the pulse) a short distance away. 4.8 Specific heat The specific heat is a measure of the amount of energy required to change the temperature of a given mass of material. Specific heat is measured by calorimetry techniques and is usually reported both as CV, the specific heat measured at constant pressure, or CP, the specific heat measured at constant pressure. 4.9 Melting point The melting point is the temperature at which a material goes from the solid to the liquid state at one atmosphere. The melting temperature is not usually a design criteria but it offers important clues to other material properties. 4.10 Glass transition temp The glass transition temperature, or Tg is an important property of polymers. The glass transition temperature is a temperature range which marks a change in mechanical behavior. Above the glass transition temperature a polymer will behave like a ductile solid or highly viscous liquid. Below Tg the material will behave as a brittle solid. Depending on the desired properties materials may be used both above and below their glass transition temperature.
58 4.11 Thermal expansion coefficient The thermal expansion coefficient is the amount a material will change in dimension with a change in temperature. It is the amount of strain due to thermal expansion per degree Kelvin expressed in units of K -1 . For isotropic materials is the same in all directions, anisotropic materials have separate "s reported for each direction which is different. 4.12 Thermal shock resistance Thermal shock resistance is a measure of how large a change in temperature a material can withstand without damage. Thermal shock resistance is very important to most high temperature designs. Measurements of thermal shock resistance are highly subjective because it is extremely process dependent. Thermal shock resistance is a complicated function of heat transfer, geometry and material properties. The temperature range and the shape of the part play a key role in the material's ability to withstand thermal shock. Tests must be carefully designed to mimic anticipated service conditions to accurately assess the thermal shock resistance of a material. 4.13 Creep resistance Creep is slow, temperature aided, time dependent deformation. Creep is typically a factor in materials above one third of their absolute melting temperature or two thirds of their glass transition temperature. Creep resistance is an important material property in high temperature design, but it is difficult to quantify with a single value. Creep response is a function of many material and external variables, including stress and temperature. Often other environmental factors such as oxidation or corrosion play a role in the fracture process. Creep is plotted as strain vs. time. A typical creep curve shows three basic regimes. During stage I, the primary or transient stage, the curve begins at the initial strain, with a relatively high slope or strain rate which decreased throughout stage I until a steady state is reached. Stage II, the steady state stage, is generally the longest stage and represents most of the response. The strain rate again begins to increase in stage III and rupture at tR generally follows quickly. The main objective of a creep test is to study the effects of temperature and stress on the minimum creep rate and the time to rupture. Creep testing is usually run by placing a sample under a constant load at a fixed temperature. The data provided from a complete creep test at a specific temperature, T,
59 and stress includes three creep constants: the dimensionless creep exponent, n, the activation energy Q, and A, a kinetic factor. Figure 4.2 Creep Resistance Figure 4.3 Properties Table of Plastics
60 CHAPTER 5 ENVIROMENTAL PROPERTIES This topic explains the environmental properties and testing of plastic materials such as chemical properties, weathering, water absorption and stress cracking. 5.1 Chemical Properties Properties that do change the chemical nature of matter. Examples of chemical properties are: heat of combustion, reactivity with water, PH, and electromotive force. The more properties we can identify for a substance, the better we know the nature of that substance. These properties can then help us model the substance and thus understand how this substance will behave under various conditions. Chemical properties are any of the properties of matter that may only be observed and measured by performing a chemical change or chemical reaction. Chemical properties cannot be determined by touching or viewing a sample; the structure of the sample must be altered for the chemical properties to become apparent. 5.1.1 Standard Practices for Evaluating the Resistance of Plastics to Chemical Reagents ( ASTM D543) There are limitations of the results obtained from these practices. The choice of types and concentrations of reagents, duration of immersion or stress, or both, level of stress, temperature of the test, and properties to be reported are necessarily arbitrary. The specification of these conditions provides a basis for standardization and serves as a guide to investigators wishing to compare the relative resistance of various plastics to typical chemical reagents. Correlation of test results with the actual performance or serviceability of plastics is necessarily dependent upon the similarity between the testing and the end-use conditions. For applications
61 involving continuous immersion, the data obtained in short-time tests are of interest only in eliminating the most unsuitable materials or indicating a probable relative order of resistance to chemical reagents. Evaluation of plastics for special applications involving corrosive conditions shall be based upon the particular reagents and concentrations to be encountered. Base the selection of test conditions on the manner and duration of contact with reagents, the temperature of the system, applied stress, and other performance factors involved in the particular application. 5.1.2 Scope These practices cover the evaluation of all plastic materials including cast, hot-molded, cold-molded, laminated resinous products, and sheet materials for resistance to chemical reagents. These practices include provisions for reporting changes in weight, dimensions, appearance, and strength properties. Standard reagents are specified to establish results on a comparable basis. Provisions are made for various exposure times, stress conditions, and exposure to reagents at elevated temperatures. The type of conditioning (immersion or wet patch) depends upon the end-use of the material. If used as a container or transfer line, immerse the specimens. If the material will only see short exposures or will be used in proximity and reagent will splash or spill on the material, use the wet patch method of applying reagent. The effect of chemical reagents on other properties shall be determined by making measurements on standard specimens for such tests before and after immersion or stress, or both, if so tested. The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only. “This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific hazards statements are given in Section 7.”
62 5.2 Weathering Weathering is the breaking down of rocks, soil and minerals as well as artificial materials through contact with the Earth’s atmosphere, biota and waters. Weathering occurs in situ, roughly translated to: "with no movement" , and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity and then being transported and deposited in other locations. Two important classifications of weathering processes exist – physical and chemical weathering; each sometimes involves a biological component. Mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure. The second classification, chemical weathering, involves the direct effect of atmospheric chemicals or biologically produced chemicals also known as biological weathering in the breakdown of rocks, soils and minerals. While physical weathering is accentuated in very cold or very dry environments, chemical reactions are most intense where the climate is wet and hot. However, both types of weathering occur together, and each tends to accelerate the other. For example, physical abrasion (rubbing together) decreases the size of particles and therefore increases their surface area, making them more susceptible to rapid chemical reactions. The various agents act in concert to convert primary minerals (feldspars and micas) to secondary minerals (clays and carbonates) and release plant nutrient elements in soluble forms. 5.2.1 How to Test Plastic Properties Artificial Weathering has been defined by ASTM as "The exposure of plastics to cyclic laboratory conditions involving changes in temperature, relative humidity and ultraviolet (UV) radiant energy, with or without direct water spray, in an attempt to produce changes in the material similar to those observed after long-term continuous outdoor exposure." Three types of light sources for artificial weathering are in common use: 1) enclosed UV carbon arc; 2) open flame sunshine carbon arc; and 3) water cooled xenon arc.Because weather varies from day to day, year to year, and place to place, no precise correlation exists between artificial laboratory weathering and natural outdoor weathering. However, standard laboratory test conditions produce results with acceptable reproducibility and which are in general agreement with data obtained from outdoor exposures. Fairly rapid indications of weatherability are therefore obtainable on samples of
63 known plastics which through testing experience over a period of time, have general correlations established. There is no artificial substitute for predicting outdoor weatherability on plastics with no previous outdoor history. ASTM E-42. 5.3 Water Absorption Water absorption is used to determine the amount of water absorbed under specified conditions. Factors affecting water absorption include: type of plastic, additives used, temperature and length of exposure. The data sheds light on the performance of the materials in water or humid environments. Figure 5.1 Water Absorption Test 5.3.1 How to Test Plastic Properties Water Absorption data may be obtained by immersion of 24 hr or longer in water at 73.4 °F. Upon removal, specimens are dried and weighed immediately. The increase in weight is reported as percent age gained. Various plastics absorb varying amounts of water, and the presence of absorbed water may affect plastics in different ways. Electrical properties change most noticeably with water absorption, and this is one of the reasons that polyethylene, because it absorbs almost no water, is highly favored as a dielectric. Plastics which absorb relatively larger amounts of water tend to change dimension in the process. When dimensional stability is required in products made of such plastics, grades with less tendency to absorb water are chosen. The water absorption rate of acetal type plastics is so low as to have a negligible effect on properties. ASTM D-570.
64 5.4 Stress Cracking Environmental Stress Cracking (ESC) is one of the most common causes of unexpected brittle failure of thermoplastic (especially amorphous) polymers known at present. Environmental stress cracking may account for around 15-30% of all plastic component failures in service. ESC and polymer resistance to ESC (ESCR) have been studied for several decades. Research shows that the exposure of polymers to liquid chemicals tends to accelerate the crazing process, initiating crazes at stresses that are much lower than the stress causing crazing in air. The action of either a tensile stress or a corrosive liquid alone would not be enough to cause failure, but in ESC the initiation and growth of a crack is caused by the combined action of the stress and a corrosive environmental liquid. It is somewhat different from polymer degradation in that stress cracking does not break polymer bonds. Instead, it breaks the secondary linkages between polymers. These are broken when the mechanical stresses cause minute cracks in the polymer and they propagate rapidly under the harsh environmental conditions. It has also been seen that catastrophic failure under stress can occur due to the attack of a reagent that would not attack the polymer in an unstressed state.
65 CHAPTER 6 OPTICAL AND ELECTRICAL PROPERTIES This topic introduces to optical and electrical properties as well as testing of plastic materials such as Spectaculars Gloss, Luminous Transmittance, colour, Index of Refraction and Dielectric Resistance. 6.1 Optical Properties The highest a.c. electrical frequencies we have discussed fall within the short radio wave and microwave regions of the electromagnetic spectrum. The transmission and absorption of radiation by the polymer dielectric are determined by the quantities e, and e". Even higher frequencies bring us into the infrared and visible parts of the spectrum, that is, to optical phenomena. In the rest of this chapter we discuss the transmission, scattering and absorption of light by polymer materials. There is an important underlying continuity in the electrical and optical behaviour of materials; for example, the optical refractive index n and the high frequency permittivity are linked in electromagnetic theory by the relation n = (e[) 2. At optical frequencies as at lower a.c. frequencies absorption of radiation occurs by irreversible non-radiative loss processes. Absorption of optical radiation occurs by excitation of bond vibrations (infrared) and rearrangements of electrons within molecules (visible and ultraviolet). 6.1.1 How to Test Plastic Properties Luminous Reflectance, transmittance and color. This test is the primary method to obtain colorimetric data. Properties determined include: 1 ) total luminous reflectance or luminous directional reflectance; 2) luminous transmittance; and 3 ) chromaticity coordinates x and y (color).A specimen is mounted in a special device and along with it a comparison surface (white chalk). The specimens are placed in the device and light of different wave-length intervals is impinged against the surface. Reflected or transmitted light is then measured to obtain property values. ASTM D-791. 6.2 Transparency Colourless polymeric materials range from highly transparent to opaque. Loss of transparency arises from light scattering processes within the material, which distort and attenuate the transmitted image.
66 6.2.1 How to Test Plastic Properties Haze and Luminous Transmittance of transparent plastics. In this test, haze of a specimen is defined as the percentage of transmitted light which, in passing through the specimen, deviates more than 2.5° from the incident beam by forward scattering. Luminous transmittance is defined as the ratio of transmitted to incident light. These qualities are considered in most applications for transparent plastics. They form a basis for directly comparing the transparency of various grades and types of plastics. A hazemeter and/or a recording spectrophotometer are used in the test. ASTM D-1003. 6.3 Colour and Infrared Absorption Very few pure polymers absorb radiation in the visible spectrum, that is, roughly between 380 and 760 nm. Thus most polymers are colourless. The only exceptions are some thermosets and elastomers, including PF, some polyurethanes, epoxies and furan resins, which absorb more or less strongly at the blue end of the spectrum and consequently appear brownish when viewed by transmitted or reflected light. These substances contain alternating double and single covalent bonds or aromatic rings which act as chromophores, absorbing light at frequencies corresponding to the excitation energies of bonding electrons. Graphite and the other polymeric carbons which have fused ring structures and which appear intensely black exhibit this absorption throughout the visible spectrum in extreme form. Deliberately coloured polymer materials are invariably produced by incorporating as additives either finely divided coloured solids (pigments) or soluble coloured substances (dyes). The colours of solid polymers are fully defined by their spectra, measured either by transmission or reflection as appropriate. It is often more useful for purposes of specification to refer to colours by using the CIE trichromatic system of colour measurement. 6.4 ELECTRICAL PROPERTIES The electrical properties of a material may be investigated by considering its response to imposed electric fields of various strengths and frequencies, just as the mechanical properties may be defined through the response to static and cyclic stress. We consider first the behaviour of polymers in steady (d.c.) electric fields.
67 6.5 Index of Refraction and Dielectric Resistance. The visual appearance and optical performance of a polymer material depends, apart from colour, on the nature of its surface and its light transmission properties. We follow the recommendations of BS4618 : Section 5.3 : 1972 and consider in turn refraction, transparency, gloss and light transfer. Refractive index is determined by the extent to which the electronic structure of the polymer molecules is deformed by the optical frequency electric field of the radiation. If a material is structurally isotropic, as in the case of unstressed amorphous polymers, then it is also optically isotropic, and a single refractive index characterises the refraction behaviour. In crystals and other anisotropic materials the refractive index takes different values along different principal axes, and the material is said to be doubly refracting or birefringent. Amorphous materials under deformation develop birefringence as molecules become aligned. 6.5.1 Arc Resistance Arc Resistance shows the ability of a plastic to resist the action of an arc of high voltage and low current close to the surface of the insulation in tending to form a conducting path therein. Arc resistance values are of relative value only in distinguishing plastics of nearly identical composition, such as for quality control, development and identification. ASTM D-495. 6.5.2 Dielectric Constant Dielectric Constant is the ratio of the capacity of a condenser made with a particular dielectric to the capacity of the same condenser with air as the dielectric. For a plastic used to support and insulate components of an electrical network from each other and ground, generally it is desirable to have a low level of dielectric constant. For a material to function as the dielectric of a capacitor, on the other hand, it is desirable to have a high value of dielectric constant, so the capacitor may be physically as small as possible. ASTM D-150. 6.5.3 Dielectric Strength Dielectric Strength is an indication of the electrical strength of a plastic as an insulator. The dielectric strength of an insulating material is the voltage gradient at which electric failure or breakdown occurs as a continuous arc (the electrical property analogous to tensile strength in mechanical properties). The dielectric strength of plastics varies greatly with several conditions, such as humidity and geometry, and it is not possible to directly apply the standard test values to field use unless all conditions, including specimen dimension, are the same.
68 Because of this, the dielectric strength test results are of relative rather than absolute value as a specification guide.The dielectric strength of polyethylenes is usually around 500 volts/mil. The value will drop sharply if holes, bubbles, or contaminants are present in the specimen being tested. Dielectric strength varies inversely with the thickness of the specimen. A specimen is placed between heavy cylindrical brass electrodes which carry electric current during the test. There are two ways of running this test for dielectric strength: 1) Short-Time: the voltage is increased from zero to breakdown at a uniform rate, 0.5 to 1.0 kc/sec. The precise rate of voltage rise is specified in governing material specifications. 2) Step-By-Step: the initial volt age applied is 50% of breakdown voltage shown by the short-time test. It is increased at rates specified for each type of material and the break down level noted. Breakdown by these tests means passage of sudden excessive current through the specimen and can be verified by instruments and visible damage to the specimen. ASTM D-149. 6.5.4 Dissipation Factor Dissipation Factor is the ratio of the real power (in phase power) to the reactive power (power 90 deg out of phase). It is also defined as the ratio of conductance of a capacitor in which the material is the dielectric to its susceptance or the ratio of its parallel reactance to its parallel resistance. It is the tangent of the loss angle and the cotangent of the phase angle. Dissipation factor is a measure of the conversion of reactive power to real power, showing as heat. ASTM D-150.5. 6.5.5 Electrical Resistance Two electrodes are placed on or embedded in the surface of a test specimen. The following properties are calculated: Insulation resistance is the ratio of direct voltage applied to the electrodes to the total current between them; dependent upon both volume and surface resistance of the specimen. In materials used to insulate and support components of an electrical network, generally it is desirable to have insulation resistance as high as possible. Volume resistivity is the ratio of the potential gradient parallel to the current in the material to the current density. Surface resistivity is the ratio of the potential gradient parallel to the current along its surface to the current per unit width of the surface. Knowing the volume and surface resistivity of an insulating material makes it possible to design an insulator for a specific application.
69 6.5.6 Loss Factor Loss Factor is the product of the dielectric constant and the power factor and is a measure of total losses in the dielectric material. ASTM D-150. 6.5.7 Volume Resistivity Volume Resistivity is the ratio of direct voltage applied to the electrodes to that portion of current between them that is distributed through the volume of the specimen.Surface resistance is the ratio of the direct voltage applied to the electrodes to that portion of the current between them which is in a thin layer of moisture or other semi-conducting material that may be deposited on the surface. High volume and surface resistance are desirable in order to limit the current leakage of the conductor which is being insulated. ASTM D-257. Based on "Standard Tests on Plastics/Bulletin GlC: 4th Edition," published by Celanese Plastics Co., Division of Celanese Corp., Newark, N. J.
LAB SHEET MANUAL 70
71 MECHANICAL PROPERTIES LAB SHEET : TENSILE TESTING At the end of this task, the student should be able to: Identify the standard and equipments used in plastic material testing. Conduct various types of plastic materials testing independently using Standard Operation Procedure. Interpret the data and result findings in plastic materials testing. Theory d = diameter gauge Lo = long gauge Lc = long parallel Diagram 2: Standard Specimen
72 Diagram 3: Curve of the nominal stress-nominal strain for the plastic material where; A,B and C = Elastic Limit D = Maximum Load E = Breaking Point a) Ultimate Tensile Strength (UTS) = Maximum Load (KN)/ Cross Cutting Area (mm²) b) Modulus of Elastic (E) = Stress (KN)/ Strain (mm²) c) Elongation Percentage = (L – Lo)/ LoX 100% where; Lo = actual gauge length L = gauge length end Ao = actual cross sectional area A = cross sectional area end Apparatus/Equipments Universal Testing Machine Extension meter Vernier Calliper Steel Ruler Specimen (Plastic Material)
73 Safety Precautions Always keep the floor clean. Always keep the floor clean. Always use the correct tool for the job. Keep tools in the boxes or racks when not in use. Operate the machine with wearing personal protective equipment such as glove and mask. Never try to bypass the guard safety interlock. Make sure that all safety devices are working properly. Procedure i. Measuring gauge diameter and length of the specimen and record in the table. ii. Shift the specimen holder to a suitable distance. iii. Pressing button to grip the handle on the specimen. iv. Compute display channel load zeroes.
74 v. Press button to bottom holder can be hold the specimen. vi. Pair the extension meter on the specimen and make sure the extension channel is zeroes. vii. Activate the trapezium software and enter the relevant data. viii. Click ‘test’ and enter the relevant data on the Perform test. ix. Setting zeroes on load then enter the values channel spell shift rate at appropriate (5mm/min). x. Click Start Test button and wait untilitshows continuous test and extension. Extension meter remove from the test piece. xi. Click Continuous Test button to continue the test until the specimen fractures. xii. Obtain the relevant graphs for the tensile test. xiii. Get a gauge diameter and length of test specimen after broken line. Result/Data Complete this below table: Measurement (mm) Origin (before test) Last (after test) Long Parallel Print a graph from a computer: i. Graph of Load (KN) versus Elongation (mm) ii. Graph of Stress(KN/mm²) versus Strain (%)
75 ACTIVITY: Calculate: 1. Ultimate Tensile Stress 2. Modulus of Elasticity 3. Percent of Elongation 4. Observations Recorded During The Test Run 5. Discussion of the Graph is Plotted 6. Overall conclusion of the experiment by making a connection to the Stress, Strain and Young Modulus.
76 Discussions i. Plot graph Stress vs Folding for each specimen. ii. Discuss the data and graph from results. iii. Discuss the test method and error of this experiment. iv. List THREE (3) suggestion to improve this experiment. Conclusion and Recommendation Your conclusion should be related to your workshop objective and suggest your recommendation to improve the quality of product. References State your reference either refer to books, articles, or journals.
77 LAB SHEET : IMPACT TEST At the end of this task, the student should be able to: Identify the standard and equipments used in plastic material testing. Conduct various types of plastic materials testing independently using Standard Operation Procedure Interpret the data and result findings in plastic materials testing. Theory Impact is a very important phenomenon in governing the life of a structure. For example, in the case of an aircraft, impact can take place by a bird hitting a plane while it is cruising, or during take off and landing the aircraft may be struck by debris present on the runway, and as well as other causes. Two types of impact testing standard izod and charpy. The Charpy impact test, also known as the Charpy V-notch test, is a standardized high strain-rate test which determines the amount of energy absorbed by a material during fracture. This absorbed energy is a measure of a given material's toughness and acts as a tool to study temperature-dependent ductile-brittle transition. It is widely applied in industry, since it is easy to prepare and conduct and results can be obtained quickly and cheaply. A major disadvantage is that all results are only comparative. Izod impact strength testing is an ASTM standard method of determining impact strength. A notched sample is generally used to determine impact strength.The test is named after the English engineer Edwin Gilbert Izod (1876–1946), who described it in his 1903 address to the British Association, subsequently published in Engineering.
78 Digital Display, J Pendulum Axis Specimen Support Frame Figure 1 : Schematic Machine Impact Test Apparatus/Equipments Impact Test Machine Specimens ( PP , PE , PS , ABS ) Safety Precautions Always keep the floor clean. Always keep the floor clean. Always use the correct tool for the job. Keep tools in the boxes or racks when not in use. Operate the machine with wearing personal protective equipment such as glove and mask. Never try to bypass the guard safety interlock. Make sure that all safety devices are working properly.
79 Procedure i. Switch on the impact machine. ii. Mount the correct pendulum according to standard method of Izod Test . Raise the pendulum so that clicks into place at the upper position of 160 o iii. Prepared the specimen (thermoplastics polyethylene) with V notching. iv. Clamp the specimen on the supports in vertical position. v. Set the drag pointer to zero. Thus the test is prepared . vi. Release the pendulum release. The pendulum drops. It hits the specimen at an impact velocity. vii. The specimen is then destroyed. The absorbed impact energy is saved via the drag pointer. viii. Read the results from the analog display and repeat the test. Result/Data Complete this below table: MATERIAL VALUE 1 VALUE 2 VALUE 3 VALUE 4 VALUE 5 AVERAGE Discussions i. How the material characteristics influences the value of energy impact for Izod Testing ? ii. List the factors influence the energy impact value. iii. List THREE(3) reasons of notching in impact test. iv. Give your conclusion about this experiment.
80 Conclusion and Recommendation Your conclusion should be related to your workshop objective and suggest your recommendation to improve the quality of product. References State your reference either refer to books, articles, or journals.
81 LAB SHEET : FALLING DART IMPACT At the end of this task, the student should be able to: Identify the standard and equipments used in plastic material testing. Conduct various types of plastic materials testing independently using Standard Operation Procedure (SOP). Interpret the data and result findings in plastic materials testing. Theory Test designation – D-1709-62 T Method A & B. The impact model has been designed for rapid fie testing in those labs ad quality control groups that require volume sampling. Generally the specifications of the manual tester (D-1065) apply, except the clamping method. There are two accepted methods for testing films strength with the Falling Dart Impact Tester. One method is the probit method, the other is the stairstep which is described in the following text. Wf = Wo + W ( A/N – ½) Where: Wf : Failure Weight Wo: Lowest Failure Weight W : Weight Increment A : Sum of all i nj terms N : Sum of all nj terms
82 Apparatus/Equipments Falling Dart Impact Machine Weight of dart 120g, 60g, 30g, 15g. and 5g Specimen plastics film, sheet, laminated Safety Precautions Always keep the floor clean. Always keep the floor clean. Always use the correct tool for the job. Keep tools in the boxes or racks when not in use. Operate the machine with wearing personal protective equipment such as glove and mask. Never try to bypass the guard safety interlock. Make sure that all safety devices are working properly. Procedure i. Switch on the falling dart impact machine. ii. Assembling the back post and dart holder the instrument should be placed on a level table of work area with approximately two square feet of working space available. iii. Set dart height loosen dart holding screw and insert stem of dart into hole until it bottoms. iv. Tighten screw to hold dart in place. v. Sample preparation , films sample should be cut 6” square. A minimum of 20 are required for a stairstep test. vi. A sample film should be placed over the fixed section of the film holder with the folder edge of the uncut seam facing up. vii. The film should be centered so that the uncut seam will be hit by the center of the dart when it falls. viii. The properly weighted dart is than mounted in the clamp, turning screw clockwise to tighten. ix. The dart is than released by turning screw counter-clockwise. x. The sample is then analyzed by first removing dart, than lifting the upper clamp ring to TNS UP position. xi. The first test drops is made at this starting weight. If the failure occurs the second drop should be made with 5 gram less on the dart (if no failure add 5 grams). xii. Record the ‘X’for failure and ‘O’ for unfailure in the test sheet.
83 Result/Data Complete this below test sheet: Missle Weight (grams) SEQUENTIAL RESULTS ni i inj N = A = Wo = W = Wf = Wo + W ( A/N – ½) Where: Wf : Failure Weight Wo: Lowest Failure Weight W : Weight Increment A : Sum of all i nj terms N : Sum of all nj terms
84 nj : total frequency of failure for a load value i : increase the number of loads on the Wo Discussions i. Plot graph Stress vs Folding for each specimen. ii. Discuss the data and graph from results. iii. Discuss the test method and error of this experiment. iv. List THREE (3) suggestion to improve this experiment. Conclusion and Recommendation Your conclusion should be related to your workshop objective and suggest your recommendation to improve the quality of product. Reference State your reference either refer to books, articles, or journals.
85 LAB SHEET : MIT FOLDING ENDURANCE TESTER At the end of this task, the student should be able to: Identify the standard and equipments used in plastic material testing. Conduct various types of plastic materials testing independently using Standard Operation Procedure (SOP). Interpret the data and result findings in plastic materials testing. Theory Folding endurance is especially applicable for papers used for maps, bank notes, archival documents etc. The direction of the grain in relation to the folding line, the type of fibres used, the fibre contents, the calliper of the test piece etc., as well as which type of folding tester that is used affect how many double folds a test piece can take.Folding endurance must not be confused with the related term fold number. Apparatus/Equipments MIT Folding Endurance Tester machine and plastics sample. Safety Precautions Always keep the floor clean. Always keep the floor clean. Always use the correct tool for the job. Keep tools in the boxes or racks when not in use. Operate the machine with wearing personal protective equipment such as glove and mask. Never try to bypass the guard safety interlock. Make sure that all safety devices are working properly.
86 Procedure TEST METHOD (A) Test Specimen Specimen size : 15 (W) x 120 (L)mm (B) Test Conditions i. Power Cord of the transformer to AC220V 1-phase power source. ii. Press down the load top knob [1], set the load pointer [3] to the desired load scale and lock the pointer with screw [4]. iii. Set the specimen to upper clamp [5], with lower clamp [6] perpendicular, loosen the screw to set the other end of the specimen set to upper clamp [5] to lower clamp [6]. And then fasten the screw of the lower clamp. iv. When the specimen is set, the specimen set to the upper and lower clamp shall be parallel and without sagging. v. Loosen the set screw(4) to apply tension. Then if the sale indication is different from the desired one, this means that the specimen is not firmly fastened. So the fastening should be done again. vi. Turn of the power sw [14] to ON. vii. Make sure if the counter [9] is set to ‘0’. viii. Press the start sw [11] to start a test. ix. When the specimen is cut off, the load pointer [3] goes back to its original position, micro sw works and then the counter and the motors stop automatically. Result/Data Complete this below table. LOAD (KG) NUMBER OF FOLDING Force F, (N) A STRESS ( N /m 2 )
87 Discussions i. Plot graph Stress vs Folding for each specimen. ii. Discuss the data and graph from results. iii. Discuss the test method and error of this experiment. iv. List THREE (3) suggestion to improve this experiment. Conclusion and Recommendation Your conclusion should be related to your workshop objective and suggest your recommendation to improve the quality of product. References State your reference either refer to books, articles, or journals.
88 PHYSICAL PROPERTIES LAB SHEET : SURFACE ROUGHNESS At the end of this task, the student should be able to: Identify the standard and equipments used in plastic material testing. Conduct various types of plastic materials testing independently using Standard Operation Procedure (SOP). Interpret the data and result findings in plastic materials testing. Theory This test is included in the category of destructive tests. Although this test does not damage the surface of the product, but the product to be tested should be cut so that it can be placed on the experimental platform. Experimental results is to obtain the value of , , and , where: = Arithmetic mean deviation of the profile =Maximum height of the profile = Ten point height of irregularities = Root mean square deviation of the profile Apparatus/Equipments SJ 201 Surface Roughness Tester (MITUTOYO) Standard Specimen injection molded products
89 Safety Precautions Always keep the floor clean. Always keep the floor clean. Always use the correct tool for the job. Keep tools in the boxes or racks when not in use. Operate the machine with wearing personal protective equipment such as glove and mask. Never try to bypass the guard safety interlock. Make sure that all safety devices are working properly. Procedure TEST METHOD i. Obtain the specimen size. ii. Set the surface roughness testing equipment. iii. Perform calibration on standard specimens. iv. Do experiments on injection molded products. v. Take a reading for value of , , and Result/Data Complete schedule of the experimental results (in µm) Discussions i. ii. Answers to the following questions: What conclusion can be made from reading the value of , , and iii. iv. v. vi. vii. Where and when these experiments should be conducted. What are the advantages in carrying out this experiment? What are the factors that influence the surface defects of plastic products What are the types of common defects in the products produced by the injection plastic molding? Name three ways to determine the quality or number of the texture on a surface.
90 Conclusion and Recommendation What is the value of observations of a sample of different luminosity? For each sample is found to be the same luminosity? Why? Reference State your reference either refer to books, articles, or journals.
91 THERMAL PROPERTIES LAB SHEET : MELT FLOW INDEX At the end of this task, the student should be able to: Identify the standard and equipment used in plastic material testing. Conduct various types of plastic materials testing independently using Standard Operation Procedure (SOP). Interpret the data and result findings in plastic materials testing. Theory The melt flow index (MFI) is a measure of the ease of flow of the melt of a thermoplastic polymer. It is defined as the mass of polymer, in grams, flowing in ten minutes through a capillary of a specific diameter and length by a pressure applied via prescribed alternative gravimetric weights for alternative prescribed temperatures. [1][2] Polymer processors usually mentally correlate the value of MFI with the polymer grade that they have to choose for different processes, and most often this value is not accompanied by the units, because it is taken for granted to be g/10min. Similarly, the test load conditions of MFI measurement is normally expressed in kilograms rather than any other units. The method is described in the similar standards ASTM D1238. Apparatus/Equipments Balance – An analytical balance capable reading 0.0001g. The test plastics specimen Melt Flow Index Tester Procedure For Determining MFI Is As Follows: i. A small amount of the polymer sample (around 4 to 5 grams) is taken in the specially designed MFI apparatus. A die with an opening of typically around 2 mm diameter is inserted into the apparatus. ii. The material is packed properly inside the barrel to avoid formation of air pockets.
92 iii. A piston is introduced which acts as the medium that causes extrusion of the molten polymer. iv. The sample is preheated for a specified amount of time: 5 min at 190 °c for polyethylene and 6 min at 230 °c for polypropylene. v. After the preheating a specified weight is introduced onto the piston. Examples of standard weights are 2.16 kg, 5 kg, etc. vi. The weight exerts a force on the molten polymer and it immediately starts flowing through the die. vii. A sample of the melt is taken after the desired period of time and is weighed accurately. Mfi is expressed in grams of polymer per 10 minutes of duration of the test. Discussions Compare each plastics specimen. Conclusion and Recommendation Your conclusion should be related to your workshop objective and suggest your recommendation to improve the quality of product. References State your reference either refer to books, articles, or journals.
93 LAB SHEET : VICAT SOFTENING POINT At the end of this task, the student should be able to: Identify the standard and equipment used in plastic material testing. Conduct various types of plastic materials testing independently using Standard Operation Procedure (SOP). Interpret the data and result findings in plastic materials testing. Theory "Vicat softening temperatue" or "Vicat hardness is the determination of the softening point for materials that have no definite melting point, such as plastics. It is taken as the temperature at which the specimen is penetrated to a depth of 1 mm by a flat-ended needle with a 1 mm 2 circular or square cross-section. For the Vicat A test, a load of 10 N is used. For the Vicat B test, the load is 50 N.Standards to determine Vicat softening point include ASTM D 1525 and ISO 306, which are largely equivalent. Apparatus/Equipments Balance – An analytical balance capable reading 0.0001g. Vicat Softening Point Machine. The test plastics specimen. Discussions Compare each plastics specimen. Conclusion and Recommendation Your conclusion should be related to your workshop objective and suggest your recommendation to improve the quality of product. References State your reference either refer to books, articles, or journals.