Bài giảng Phân tích polyme

TRƯỜNG ĐẠI HỌC BÁCH KHOA ĐÀ NẴNG KHOA HOÁ PHÂN TÍCH POLYME (POLYMER ANALYSIS) TS. Đoàn Thị Thu Loan §§§ üIs a branch of polymer science dealing with analysis and characterisation of polymers. üThe complication of macromolecular chains, the dispersion in molecular weight, tacticity, crystallinity, orientation, composition of polymers etc. and complex morphological systems Þ analysis of polymer ¹ the small organic materials Þ Focus on viscoelastic properties, dynamic mechanical testing. Polymer analysis ·Instron mechanical tester ·Vicker hardness tester ·DMA ·Melt flow indexer ·Torsions Rheometer · ·-AFM, SEM ·-FT-IR ·-Pull-out test Instruments ·FT-IR ·IR-microscope ·GPC ( size exclusion chromatography SEC) ·-Viscosimetry ·-X-ray (WAXS and SAXS) ·-EM, SEM, TEM, AFM ·-Dynamic and static methods for contact angle measurements. -Tensile, flexural, impact, compression, hardness tests, -Rheological and viscoelastic properties, stiffness and modulus, surface tension, permeation and diffusion in polymers, adhesion tests, density -Surface roughness, -Chemical composition, -Interface characetrisation -Molecular weight determination, -Microstructural characterisation and compositional analysis, -Crystallinity, -Investigation of polymer morphology, particle size, -Contact angle and wettability measurements Mechanical and Physical Properties Surface Characterisation Chemical, Molecular and Structural Characterisation Methods of polymer analysis ·GC ·pH meter ·HPLC ·Karl-Fischer titration ·Thermogravimetric analyser (TGA) ·TGA-FTIR coupled technique ·Differential scanning calorimetry (DSC) ·Modulated differential scanning calorimetry (ADSC) ·Dynamic thermomechanical analyser (DMTA) ·Dielectric relaxation Instruments Inolab conductivity meter · Purity and molecular weight of small molecules, water content in organic solvents, surface tension measurement, pH -Melting point, glass transition temperature, free rotation temperature, -Degradation and stability behaviour of polymers Conductivity, electric current in solution, light emitting and electromagnetic properties Miscellaneous (hon tap)Thermal BehaviourElectrical and Optical Properties Methods of polymer analysis -For quality control -For predicting service performance -To generate design data -To investigate failures Purpose of polymer analysis Essential to identify the purpose of testing, because the requirements for each of the purposes are different. -Precision -Reproducibility -Rapidity Balance of these attributes, according to the purpose of the test -Complexity -Automated test -Nondestructive test -Cost üNondestructive methods are advantageous and indeed essential when 100% of the output is being tested. üThe tests should be simple and inexpensive, and automation will probably aid the rapidity of testing. üTests related to product performance are preferred. Quality Control Tests üThe most important factor is that the tests relate to service conditions and to aspects of product performance. üshould not be too complex, although rapidity and cheapness are less important than was the case with quality control. üNondestructive tests are not always appropriate when predicting product performance, as it may be necessary to establish the point at which failure occurs. Tests Predicting Product Performance üUsually test pieces are of a simple shape and a specified size, whereas the product may be of a different geometry and size üData must be presented in a form that enables the designer to allow for changes in geometry, time scale, etc.. which implies detailed and comprehensive understanding of material behavior üIt follows that data of this type are expensive to produce and that results are unlikely to be obtained with great rapidity. üHowever, automation may be advantageous, particularly in the case of tests running for a long time (creep tests) Tests for Producing Design Data üSome understanding of the various mechanisms of failure is necessary before suitable tests can be chosen. ü Tests need not be complex but must be relevant Ex: a simple measurement of product thickness may establish that there has been a departure from the specified design thickness. üThe absolute accuracy of the test may not be important, but it is essential that it be capable of discriminating between the good and the bad product. Tests for Investigating Failures What are our expectations of polymer materials? •Excellent Characteristics: Mechanical and Physical Properties Thermal Behaviour Surface and interface Characteristics Electrical and Optical Properties•Safe to use •Light weight •Reliable, durable •Low cost •Less adverse environmental impact •Good resistance to environmental attacks Mechanical Testing of Polymers Types of Mechnical Tests Tensile test (a) Flexural test (d) (e) (f) Compression test (b) Shear (g) (h) (i) Impact test (h) (i) Scope: üMeasure the force required to break a specimen and the extent to which the specimen stretches or elongates to that breaking point. üProduce a stress-strain diagram, which is used to determine tensile modulus. üThe data is often used to specify a material, to design parts to withstand application force and as a quality control check of materials. üSince the physical properties of many materials (especially thermoplastics) can vary depending on ambient temperature Þ test materials at temperatures that simulate the intended end use environment. Tensile test Specimen Size: üThe most common specimen for ISO 527 is the ISO 3167 Type 1A multipurpose specimen. üASTM D882 uses strips cut from thin sheet or film. *The multipurpose test specimen: +150 mm long, +The center section: 10 mm wide *4 mm thick *80 mm long. Tensile test A tensile dog bone specimen b W l d For the composite samples Longitudinal test Transverse test Test Procedure: üSpecimens are placed in the grips and pulled until failure. üFor ASTM D638, the test speed is determined by the material specification. üFor ISO 527 the test speed is typically 5 or 50mm/min for measuring strength and elongation +and 1mm/min for measuring modulus. ü An extensometer is used to determine elongation and tensile modulus. Tensile test Tensile2.wmv Characteristics of stress-strain behavior: ü Modulus of elasticity (stiffness, elastic modulus, Young’s modulus) is the slope of the stress-strain curve in the elastic region ü Yield strength (sy) is the stress applied to a material that just causes permanent deformation ü Tensile strength (TS) is defined at the fracture point and can be lower than the yield strength ü Ultimate tensile strength is the stress that corresponds to the maximum load ü Elongation at break (%e) – the increase in length of a specimen under tension before it breaks (Strain). Stress –Strain Behavior P= Applied load A = Original cross-sectional area Strain, e S tre ss , s sy ey eF sF 2%0 · E = d/l Stress-train behavior of polymers Stress –Strain Behavior üModuli of elasticity for polymers are ~ 10MPa-4GPa (compare to metals ~ 50 - 400 GPa) üTensile strengths are ~ 10 -100MPa (compare to metals, hundreds of MPa to several GPa) üElongation can be up to 1000 % in some cases (< 100% for metals) üPolymers are also very sensitive to the rate of deformation (strain rate). Decreasing rate of deformation has the same effect as increasing T. Stress –Strain Behavior TENSILE RESPONSE: ELASTOMER CASE Deformation of Amorphous Polymers Stress-strain curves Deformation of Semicrystalline and crosslinked Polymers Flexural test Scope: üMeasures the force required to bend a beam under 3 point loading conditions. üThe data is often used to select materials for parts that will support loads without flexing. üFlexural modulus is used as an indication of a material’s stiffness when flexed. ücan test materials at temperatures that simulate the intended end use environment. ü Most commonly the specimen lies on a span and the load is applied to the center by the loading nose producing three point bending at a specified rate. üThe parameters for this test are : +The support span; +The speed of the loading +The maximum deflection for the test. These parameters are based on the test specimen thickness, and are defined differently by ASTM and ISO. Specimen Size: üA variety of specimen shapes can be used üThe most commonly used specimen size: + 3.2mm x 12.7mm x 125mm for ASTM D790 +10mm x 4mm x 80mm for ISO 178 Test Procedure: Flexural test üFlexural strength üFlexural modulus Flexural test b b L F d 3 3 4 hb LmEb = 22 3 hb LF b =s m : initial slope of the load vs. deflection curve For relatively thin samples ® two point loading For thick samples ® 4 point loading Flexural test Izod Impact Testing (Notched Izod) üNotched Izod Impact is a single point test that measures a materials resistance to impact from a swinging pendulum. ü Izod impact is defined as the kinetic energy needed to initiate fracture and continue the fracture until the specimen is broken. üIzod specimens are notched to prevent deformation of the specimen upon impact. üThis test can be used as a quick and easy quality control check to determine if a material meets specific impact properties or to compare materials for general toughness. Scope: ü 64 x 12.7 x 3.2 mm for ASTM D256 üThe preferred thickness is 6.4 mm because it is not as likely to bend or crush üThe depth under the notch of the specimen is 10.2 mm ü80 x 10 x 4 mm for ISO 180 üThe depth under the notch of the specimen is 8mm Specimen Size: Izod Impact Testing (Notched Izod) üThe specimen is clamped into the pendulum impact test fixture with the notched side facing the striking edge of the pendulum. üThe pendulum is released and allowed to strike through the specimen. üIf breakage does not occur, a heavier hammer is used until failure occurs. üSince many materials (especially thermoplastics) exhibit lower impact strength at reduced temperatures Þ to test materials at temperatures that simulate the intended end use environment izodimpact.wmv Izod Impact Testing (Notched Izod) Test Procedure: üThe specimens are conditioned at the specified temperature in a freezer until they reach equilibrium. üThe specimens are quickly removed, one at a time, from the freezer and impacted. üNeither ASTM nor ISO specify a conditioning time or elapsed time from freezer to impact - typical values from other specifications are 6 hours of conditioning and 5 seconds from freezer to impact. Reduced Temperature Test procedure: ASTM üImpact energy is expressed in J/m or ft-lb/in. üImpact strength is calculated by dividing impact energy in J (or ft-lb) by the thickness of the specimen. üThe test result is typically the average of 5 specimens. ISO üImpact strength is expressed in kJ/m2 üImpact strength (acU) is calculated by dividing impact energy in J by the area under the notch. Data 3 cU 10a ´= bh W W: energy b = width of the sample h = thickness of the sample üThe test result is typically the average of 10 specimens. The higher the resulting number, the tougher the material. Impact Testing üCompressive properties describe the behavior of a material when it is subjected to a compressive load. üLoading is at a relatively low and uniform rate. üCompressive strength and modulus are the two most common values produced. Compression test üBlocks or cylinders üFor ASTM D695: +The typical blocks: 12.7 x 12.7 x 25.4mm +The cylinders:12.7mm diameter and 25.4mm long üFor ISO 604: the preferred specimens: +50 x 10 x 4mm for modulus +10 x 10 x 4mm for strength Specimen size: Scope: üThe specimen is placed between compressive plates parallel to the surface. üThe specimen is then compressed at a uniform rate. üThe maximum load is recorded along with stress-strain data. üAn extensometer attached to the front of the fixture is used to determine modulus. Compression test Compressive strength maximum compressive load minimum cross-sectional area = Compressive modulus change in stress change in strain = Test Procedure: Rockwell Hardness tester üStandard specimen of 6.4mm thickness ü is molded or cut from a sheet. Specimen size: ü A hardness measurement based on the net increase in depth of impression as a load is applied. üHardness numbers have no units and are commonly given in the R, L, M, E and K scales. üThe higher the number in each of the scales, the harder the material üThe harder the material ® better resistance to plastic deformation or cracking in compression, better wear properties Scope: Durometer Hardness - Shore Hardness üDetermine the relative hardness of soft materials, usually plastic or rubber. üThe test measures the penetration of a specified indentor into the material under specified conditions of force and time. üThe hardness value is often used to identify or specify a particular hardness of elastomers or as a quality control measure on lots of material. Scope: üGenerally 6.4mm (¼ in) thick for ASTM D 2240. Specimen size: Durometer Hardness - Shore Hardness üThe specimen is first placed on a hard flat surface. üThe indentor for the instrument is then pressed into the specimen making sure that it is parallel to the surface. üThe hardness is read within one second (or as specified by the customer) of firm contact with the specimen. Test Procedure: üThe hardness numbers are derived from a scale. üShore A and Shore D hardness scales are common, with the A scale being used for softer and the D scale being used for harder materials. Data: ü Density is the mass per unit volume of a material. ü Specific gravity is a measure of the ratio of mass of a given volume of material at 23°C to the same volume of deionized water. üSpecific gravity and density are especially relevant because plastic is sold on a cost per pound basis and a lower density or specific gravity means more material per pound or varied part weight. Density and Specific Gravity ASTM D792, ISO 1183 Scope: ü For sheet, rod, tube and molded articles. üThe specimen is weighed in air then weighed when immersed in distilled water at 23°C using a sinker and wire to hold the specimen completely submerged as required. Density and Specific Gravity are calculated. üAny convenient size +Specific gravity = a/[(a + w)-b] a = mass of specimen in air. b = mass of specimen and sinker (if used) in water. W = mass of totally immersed sinker if used and partially immersed wire. +Density, kg/m3 = (specific gravity) x (997.6) Test procedures: üBulk density is defined as the weight per unit volume of material. üBulk density is primarily used for powders or pellets. üThe test can provide a gross measure of particle size and dispersion which can affect material flow consistency and reflect packaging quantity. üA funnel is suspended above a measuring cylinder. üThe funnel is filled with the sample and allowed to freely flow into the measuring cylinder. üThe excess material on top of the measuring cylinder is scraped off with a straight edge. üThe sample and the cylinder is then weighed and the weight / volume (Bulk Density) is determined. üApparent density value is recorded as g/cm3 Bulk Density ASTM D1895B Thermal Analysis üThermal analysis (TA) is frequently used to describe analytical experimental techniques which investigate the behaviour of a sample as a function of temperature. TA refers to conventional TA techniques such as: +Differential thermal analysis (DTA) +Differential scanning calorimetry (DSC) +Dynamic mechanical analysis (DMA) +Thermogravimetry (TG/TGA) Representative TA curves The advantages of TA over other analytical methods can be summarized as follows: (i) the sample can be studied over a wide temperature range using various temperature programmes (ii) almost any physical form of sample (solid, liquid or gel) can be accommodated using a variety of sample vessels or attachments (iii) a small amount of sample (0.1 µg-10 mg) is required (iv) the atmosphere in the vicinity of the sample can be standardized (v) the time required to complete an experiment ranges from several minutes to several hours (vi) TA instruments are reasonably priced Thermal Analysis Scope: üAs the sample goes through the programmed temperature change, there is no temperature difference until the sample undergoes an exothermic or endothermic chemical reaction or change of physical state. üThe thermal event (a temperature difference between the sample and the reference (DT)) will be recorded®DT versus time or temperature plot üMeasure the differential temperature between a sample and a reference pan ® to determine the temperature of the transitions Test procedures: Differential thermal analysis (DTA) Schematic of a DTA apparatus Differential thermal analysis (DTA) A DTA curve The subscripts represent: s-sample, r-reference, i-initial,f-final. Tr Tg = Glass Transition Temperature = The temperature (°C) at which an amorphous polymer or an amorphous part of a crystalline polymer goes from a hard, brittle state to a soft, rubbery state. Tm = melting point = The temperature (°C) at which a crystalline polymer melts. DHm = the amount of energy in (joules/gram) a sample absorbs while melting. Tc = crystallization point = is the temperature at which a polymer crystallizes upon heating. DHc = the amount of energy (joules/gram) a sample releases while crystallizing. The data can be used to identify materials, differentiate homopolymers from copolymers or to characterize materials for their thermal performance. Differential Scanning Calorimeter(DSC) Scope: DSC measures: üA sample of 10 to 20 mg in an aluminum sample pan is placed into the differential scanning calorimeter. üThe sample is heated at a controlled rate (usually 10°/min) üa plot of heat flow versus temperature is produced. üThe resulting thermogram is then analyzed. Test Procedure: Dsc3.wmv DSC 1. Does the sample contain volatile components? ü 2 to 3% water/solvent can lower the glass transition temperature (Tg) by up to 100oC ü Evaporation creates endothermic peaks in standard (non-hermetic) DSC pans and can be suppressed with use of hermetic DSC pans. 2. At what temperature does the sample decompose? ü Set the upper limit of the DSC experiment based on decomposition temperature (TGA). No meaningful DSC data can be obtained once decomposition results in a 5% weight loss ü Decomposition affect: the quality of the baseline due to both endothermic and exothermic heat flow, the quality of the baseline for future experiments and can affect the useful lifetime of the DSC cell due to corrosion. Some factors influence on DSC resultsc 3. How does thermal history (temperature and time) affect DSC results on the sample? 4. Identical materials can look totally different based on: - Storage temperature and time. - Cooling rate from a temperature above Tg or above the melting point. - Heating rate. - Different kinds of experiments may need to be performed in order to measure the current structure vs. comparing samples to see if the materials are the same. Some factors influence on DSC results 5. How is the Influence of the atmosphere (air or inert gases (N2, argon,..)) Use >10oC/min heating rates Tg sensitivity Thermogravimetry (TG) üTo characterize the decomposition and the thermal stability of materials. üTo provide an indication of the composition of the sample, including volatiles and inert filler ü