Polymer Physical Testing & Analysis PDF

POLYMER PHYSICAL TESTING & ANALYSIS PST472 CHAPTER 1: INTRODUCTION  LEARNING OUTCOMES At the end of this chapter, students should be able to: 1. Describe the concept of physical testing, standardization and specification. 2. Describe the two methods of test specimen preparation. 3. Discuss th...

POLYMER PHYSICAL TESTING & ANALYSIS PST472 CHAPTER 1: INTRODUCTION  LEARNING OUTCOMES At the end of this chapter, students should be able to: 1. Describe the concept of physical testing, standardization and specification. 2. Describe the two methods of test specimen preparation. 3. Discuss the purposes of conditioning the test specimen. 4. Explain the significance of physical testing on the polymeric materials.  BASIC CONCEPT  Polymeric materials are in many ways very distinct from conventional materials such as metals and glasses. Thus, polymers are unique.  They have different physical and chemical properties suited to different applications.  One of the most factor in the performance of these materials is the physical and mechanical properties of the materials and products.  These properties tell a polymer scientist or engineer many of the things he or she needs to know when considering how a polymer can be used.  Therefore, it is important to gain knowledge in physical testing for plastics and rubbers.  BASIC CONCEPT 1) Mechanical properties of solids:  Usually determined by test resulting in various deformation-vs-stress dependencies, such as stress- strain diagrams.  Examination of such dependencies readily brings out characteristics of elasticity, plasticity, and strength. 2) Mechanical properties of liquids:  Assessed by studying the dependence of the rate of strain on the stress applied.  One of the most common mechanical characteristics determined in this way is viscosity.  Classification of tests:  The tests performed on plastics and rubbers can be grouped in various ways : Tensile Test Volume Impact Test resistivity Flexural Mechanical Dielectric Electrical Test properties strength properties Tear Test Dielectric constant Flow/ Thermal processabili properties ty properties VSP HDT MFI  Classification of tests:  For reasons of speed, economy and convenience, tests such as tensile strength measurement and impact strength determination are the ones most often employed.  These are both examples of mechanical tests; sometimes referred to as physical property determinations.  Standard testing can be viewed as a convenient shortcut, which allows the rapid generation of quantitative information on material properties.  MECHANICAL PROPERTIES OF PLASTICS A material’s response to a load. The mechanical properties of a polymer involve its behavior under stress.  How strong is the polymer? How much can you stretch it before it breaks?  How stiff is it? How much does it bend when you push on it?  Is it brittle? Does it break easily if you hit it hard?  Is it hard or soft?  Does it hold up well under repeated stress?  MECHANICAL PROPERTIES OF PLASTIC Basic material properties: General properties Electrical Weight:Density , Mg/m3 properties Expense: Cost/kg , Conductor? Mechanical properties RM/kg Insulator? Stiffness: Young’s modulus E, GPa Strength: Elastic limit y , MPa Fracture strength: Tensile strength ts , MPa Brittleness: Fracture toughness Kic , Thermal MPa.m 1/2 properties Expansion: Expansion coeff. , 1/K Conduction: Thermal conductivity , W/m.K  MECHANICAL PROPERTIES OF PLASTIC The mechanical behavior of polymers is however dependent on many factors, including:  polymer type  molecular weight  test procedure  test temperature  rates. This can be especially important to the designer when the product is used or tested at temperatures near the glass transition temperature (T g) where dramatic changes in properties occur.  Mechanical properties Formabili Toughnes Strength Rigidity Durability ty s Tensile, Modulus of Impact % strength, Yield, elasticity, Hardness elongation, Notch Compressio Flexural , wear % reduction sensitivit n, Flexural, modulus resistanc in area y Shear, e, fatigue Creep, strength Stress rupture Serviceability factors and related mechanical properties. STANDARDIZATI ON  Standardization is the requirement for testing.  The mechanical tests that have been devised fall into 2 main categories: i. Those which are suitable for quality control and specification purposes, and ii. Those which yield data suitable for design purposes.  Whether a test is used to determine an absolute value of a property (for research) or whether its purpose is routine quality control, a major requirement of the test is that it should be repeatable. STANDARDIZATI ON  People in the same laboratory, or in different laboratories, should be able to get the same result on the same material.  Since there are a large number of factors (such as test machine design, test piece size, shape and method of production, testing temperature, etc. which will influence the result obtained, it is obvious that standardisation of test methods is essential.  To achieve this, various organizations have evolved in many countries and each organization prepared and issues standards suitable for testing a wide range of materials. STANDARDIZATI ON  Organization for standardization of test method: MS Malaysia standard ISO International Standards organization BSI British Standards Institution American Society for the Testing of ASTM Material FDA Food and Drug Administration DIN Deutsche Industrie Norm STANDARDIZATI ON of standard tests is normally the work The development of committees and is based on experience and agreement. Each standard test is the subject of a document, written in such a way that a good technician, with access to appropriate commercial equipment, will find all the information needed to carry out the test and to obtain results that should not depend significantly on human errors. Each standard test is given as a code number by the sponsoring organization, for example:  ASTM D790 Flexural test  ISO 178  TEST SPECIMEN PREPARATION Most standard test require the use of test specimen of specific geometry (shape and dimensions). The method of preparation of test specimens depends on a number of factors, including the type of polymer and the form in which the material is available. There are 2 methods of test specimen preparation: 1. Test specimen for soft / thin plastics or elastomeric flat stock (films, sheet, etc.):  Test specimen can be stamped out (die-cut) with a suitable sharp cutter.  TEST SPECIMEN PREPARATION 2. Test specimen for rigid plastics:  Test specimen can be molded into the desired a)Injection molding: shape.  It is a rapid way of b)Compression and transfer obtaining many test molding: specimens.  It is the most convenient  Disadvantages: method for thermosetting  The specimens can plastics and vulcanized or reactive elastomers. feature a non- homogeneous structure.  It is not representative of  Non-homogeneous most commercial fabrication processes for thermoplastics. orientation (anisotropy).  Disadvantages:  The properties can be affected significantly by  Slow process. the process parameters.  Tends to give  CONDITIONIN G The properties of polymeric materials tend to be strongly affected by temperature, and therefore, important to specify the temperature of the material during a test. A number of polymeric materials (polyamides, cellulosics, etc.) can absorb small amounts of water (moisture), which affects many of their properties. As a result, no matter which test method is employed, it is important to ensure that the samples have received the same conditioning before testing.  CONDITIONIN G Test specimen conditioning is defined as reaching thermal and moisture equilibrium. For many materials, this conditioning is simply storing the specimens at a standard temperature before testing. Conditioning is important to stabilize the polymer samples, hence give an accurate test result. Standard conditioning temperature: lab temperature at 23±2°C (73.4°F).  WHY PHYSICAL TESTING? 1. For Quality Control  To ensure that polymer process and manufactured article perform satisfactory and uniformly.  Incoming materials (raw materials), in-process materials & finished product. 2. For Research and Development (R & D)  Research: to understand process, mechanism and performance of article.  Development: to developed new (improved) process and article.  WHY PHYSICAL TESTING? 3. For standards & specifications test  To follow specification as per standard in order to ensure the good quality of manufactured article/products. 4. The other reasons for testing are: To prove design concepts To provide a basis for reliability Safety To verify the manufacturing process To evaluate competitors’ products To establish a history for a new materials  WHY PHYSICAL TESTING? Within the family of plastics and rubbers, properties vary widely and, furthermore, the properties of an individual polymer can be dramatically altered by compounding with other ingredients or by altering the processing conditions. Consequently the measurement of physical properties (the physical testing of plastics and rubbers) is extremely important in the development of science and technology of those materials.  MATERIALS INFORMATION FOR DESIGN What do we need to know about materials to design a product? Data Statisti Selection of Economic analysis capture cal material and process and business case analysis Mechanical Properties Bulk Modulus 4.1 - 4.6 GPa $ Compressive Strength 55 - 60 MPa Ductility 0.06 - 0.07 Elastic Limit 40 - 45 MPa Endurance Limit 24 - 27 MPa Fracture Toughness 2.3 - 2.6 MPa.m1/2 Hardness 100 - 140 MPa Loss Coefficient 0.009- 0.026 Modulus of Rupture 50 - 55 MPa Poisson's Ratio 0.38 - 0.42 Shear Modulus 0.85 - 0.95 GPa Tensile Strength 45 - 48 MPa Young's Modulus 2.5 - 2.8 GPa Test Test data Design data Potential Successful applications applications Characterisation Selection and implementation  PURPOSE OF SPECIFICATIONS There are many reasons for writing specifications, but the major reason is to help the purchasing department purchase equipment, materials, and products on an equal basis. The specifications, generally written by the engineering department, allow the purchasing agent to meet his requirements and ensure that the material received at different times is within the specified limits. The specification is intended to ensure batch-to-batch uniformity, as well as remove confusion between the purchaser and supplier—we all know that more often than not what is provided by the supplier is not what is expected by the purchaser.  POLYMER PHYSICAL TESTING Plastic Rubber Tensile Test Tensile Test Density Density Impact Test Hardness Test Flexural Properties Cure Test Mooney Viscosity Melting and Test Softening Test Tear Test Fatigue / Flex Cracking Test Abrasion / Wear Test Resilience Test