1. Plastics Testing: Techniques & Instruments for the Processor Dr Bob Jones Department of Mechanical Engineering University of Texas – Pan American

2. Overview Material Properties & Microstructure Material Properties & Microstructure*BREAK* Test Types Test Types Coupon tests versus product tests Coupon tests versus product tests Sample/Specimen preparation Sample/Specimen preparation Instrument selection for QC labs Instrument selection for QC labs

3. Key Mechanical Properties STIFFNESS (modulus) is resistance to deformation STIFFNESS (modulus) is resistance to deformation STRENGTH (yield or flow stress) measures resistance to permanent deformation STRENGTH (yield or flow stress) measures resistance to permanent deformation ULTIMATE STRENGTH measures resistance to failure. ULTIMATE STRENGTH measures resistance to failure. TOUGHNESS is a measure of energy absorbed in failure or resistance to growth of a crack. TOUGHNESS is a measure of energy absorbed in failure or resistance to growth of a crack.

4. Stress -Intensity of Force -Stress = force /area

5. Types of Stress Normal : load perpendicular to cross-section

6. Types of Stress Shear : load parallel to cross-section

7. Strain: Intensity of Deformation e = dl / lo

8. Relating Stress and Strain S = E e Stress = Young’s modulus x strain

9. Results of Tensile or Flex Test

12. Viscoelastic Creep

13. Microstructure Elements Molecule Length Morphology Molecule Arrangement Intermolecular Bonds Fillers & Modifiers

14. Microstructure Tests Measurement/characterization of the condition and arrangement of molecules and additives within a plastic system Measurement/characterization of the condition and arrangement of molecules and additives within a plastic system Process parameters most often affect properties by altering microstructure Process parameters most often affect properties by altering microstructure

15. Molecular Weight Average Length of molecules Average Length of molecules Determines processing characteristics and some mechanical properties Determines processing characteristics and some mechanical properties Usually measured by resin manufacturer Usually measured by resin manufacturer

16. Effect of Molecular Weight on Mechanical Properties

17. Molecular Morphology ThermosetThermoplastic Network Cross-link density Network strain Glass transition temperature AmorphousCrystalline Degree of crystallization Type of crystals Glass transition Orientation

18. Semicrystalline Thermoplastic Microstructure

19. Crystals Callister, Materials Science & Engineering An introduction, Wiley

20. Chains assume folded chain conformation These collect into lamellar crystallites Callister, Materials Science and Engineering An Introduction, Wiley

21. Calister, Materials Science and Engineering an Introduction, Wiley

22. Two crystalline morphologies Spherulite (no shear) (no shear) Row Nucleated (shear)Shish-kebab

24. Effects of Crystallization Increases Modulus (stiffness) Modulus (stiffness) Strength Strength Density Density Chemical Resistance Chemical Resistance Thermal stability Thermal stability Hardness HardnessDecreases Toughness Toughness Permeability Permeability

25. Thermoset Morphology Cross-Link Bond Backbone bond

26. Measurement of Network Structure Best Indicator of network intensity (crosslink density, crosslink functionality) is Glass transition temperature Best Indicator of network intensity (crosslink density, crosslink functionality) is Glass transition temperature

27. Glass Transition Temp. 1.Polymer goes from Glassy/Rigid behavior to rubbery/flexible 2.Breakdown of Van Der Waals Forces 3.Onset of large scale molecular motions 4.Important in amorphous polymers – not as significant in crystalline materials.

28. Dynamic Mechanical Analysis: Modulus & Temperature

29. Molecular Orientation Failure process depends on molecular orientation Failure process depends on molecular orientation Generally more orientation = greater toughness Generally more orientation = greater toughness

30. Processing Affects Morphology Crystallization takes time so cooling rate is critical Crystallization takes time so cooling rate is critical Shear during mold filling or drawing can create row nucleated structure or orient molecules Shear during mold filling or drawing can create row nucleated structure or orient molecules Curing rate and temperature determine network structure in thermosets Curing rate and temperature determine network structure in thermosets

31. Issues in Filler/Modifier Morphology Loading level – absolute amount of filler or modifier Loading level – absolute amount of filler or modifier Dispersion or distribution – clumping or orientation of material can dramatically affect performance Dispersion or distribution – clumping or orientation of material can dramatically affect performance Coupling – quality of bonding between polymer and modifier is critical for optimum performance Coupling – quality of bonding between polymer and modifier is critical for optimum performance

32. Test Classifications Microstructural Microstructural Degree of Cure or CrystallizationDegree of Cure or Crystallization Additive levels, distributionAdditive levels, distribution Mechanical Mechanical Strength,Toughness, HardnessStrength,Toughness, Hardness Physical Physical Optical propertiesOptical properties Thermal propertiesThermal properties Electromagnetic propertiesElectromagnetic properties

33. Coupon vs. Article Testing Article Testing Article Testing Result often just a pass/failResult often just a pass/fail Test is often awkward or expensiveTest is often awkward or expensive Includes effect of processingIncludes effect of processing May allow for testing of complex service and processing interactionsMay allow for testing of complex service and processing interactions Results are often difficult to relate back to particular process or material problem ---- not good for process controlResults are often difficult to relate back to particular process or material problem ---- not good for process control

34. Coupon vs. Article Testing Coupon Testing Coupon Testing Result is usually a continuous variableResult is usually a continuous variable Doesn’t necessarily include all processing effectsDoesn’t necessarily include all processing effects Will generally be directly related to material or process factorWill generally be directly related to material or process factor More useful in process control and product engineeringMore useful in process control and product engineering

35. Test Type (Common at UTPA) Coupon Article Tensile Tensile Flexural Flexural Compression Compression Impact Impact DMA DMA TMA TMA DEA DEA Hardness Hardness DSC DSC TGA TGA

36. Differential Scanning Calorimetry Small sample (10 mg) Small sample (10 mg) Heat flow into sample measured Heat flow into sample measured Heat capacity measured Heat capacity measured Tg, melting, cure crystallization, decomp, volatiles Tg, melting, cure crystallization, decomp, volatiles

37. Thermogravimetric Analysis Weight change with temperature Weight change with temperature

38. Dynamic Mechanical Analysis Many load configurations Many load configurations Oscillating load Oscillating load Changing temperature Changing temperature Continuous measurement Continuous measurement

39. DMA Results Tg Tg Temperature dependence of modulus Temperature dependence of modulus Sensitive to small changes in composition or morphology Sensitive to small changes in composition or morphology

40. Thermo-Mechanical Analysis Expansion of sample measured Expansion of sample measured Temperature varied Temperature varied Continuous measurement Continuous measurement

41. Sample Preparation/Collection Avoid conditions which deviate from actual product conditions – Avoid conditions which deviate from actual product conditions – TemperatureTemperature Excess stress or strain applicationExcess stress or strain application Chemical exposureChemical exposure For warranty returns, if possible, test failed components not just samples from same lot For warranty returns, if possible, test failed components not just samples from same lot

42. Minimum Equipment for Plastics QC Lab Linear measurement (calipers) Linear measurement (calipers) Analytical balance Analytical balance Oven Oven Instruments required by customers (colorimeter, reflectometer, etc) Instruments required by customers (colorimeter, reflectometer, etc)

43. Recommended Equipment for QC Lab Differential Scanning Calorimeter (DSC) – virtual requirement for thermosetting processors Differential Scanning Calorimeter (DSC) – virtual requirement for thermosetting processors Durometer or other hardness tester Durometer or other hardness tester

44. Nice to Have in QC Lab Small universal testing machine (tensile, flex, compression testing) Small universal testing machine (tensile, flex, compression testing) Pendulum impact tester (Izod) Pendulum impact tester (Izod) Melt Indexer (if regrind blending is done or for acceptance testing of non-certified material) Melt Indexer (if regrind blending is done or for acceptance testing of non-certified material)