Report

DYNAMIC MECHANICAL ANALYSIS

Course: Synthesis and Characterization of Macromolecules

Course Code: PST 522E

Submitted By,

Shahrukh Shahbaz

Student No. 503131814

Date: April 30th, 2015

Istanbul Technical University, Istanbul, TurkeyTable of Contents1INTRODUCTION32Working Principle of a Dynamic Mechanical Analyzer33YOUNG MODULUS OF SOME COMMON POLYMERS54DEFINITIONS:64.1YOUNGS MODULUS:64.2LOSS MODULUS:64.3STORAGE MODULUS:64.4TAN (DELTA):74.5TOUGHNESS:75EXPERIMENTAL:85.1MATERIALS85.2METHOD86RESULTS:96.1Graphs96.2Youngs Modulus:106.3Ultimate Stress:106.4Yield Point106.5Proportionality116.6Elastic Limit116.7Toughness117CONCLUSION AND DISCUSSION118REFERENCES129SUMMARY (ARTICLE):13

INTRODUCTIONDMA is a technique where a small deformation is applied to a sample in a cyclic manner. This allows the materials response to stress, temperature, frequency and other values to be studied.Dynamic Mechanical Analysis (DMA) measures the mechanical properties of materials as function of temperature, frequency and time and also it is a thermal analytical method by which the mechanical response of a sample subjected to a specific temperature program is investigated under periodic stress. Dynamic mechanical analyzer is a thermal analytical instrument used to test the mechanical properties of many different materials.The Dynamic Mechanical Analysis is a high precision technique for measuring the viscoelastic properties of materials. Viscoelasticity is about elastic behaviors of material. Most real-world materials exhibit mechanical responses that are a mixture of viscous and elastic behavior.Working Principle of a Dynamic Mechanical AnalyzerDynamic mechanical analyzers can be divided into two main categories: Stress (force) controlled Strain (amplitude) controlledDMA Q800 (TA Instruments) is a typical example of a stress-controlled instrument. As shown in Figure 4 in a stress controlled DMA, a motor applies a force (stress) to the sample and a displacement sensor measures the strain. While running an experiment, the instrument such as DMA Q800 simply applies force until it achieves the pre-set amplitude. As the sample stiffness varies considerably during the test, applied control force also varies to maintain the measured pre-set amplitude. Typical output signals from DMA Q800 include storage modulus, loss modulus, loss tangent, sample stiffness as a function of temperature and frequency.

Figure: A schematic diagram of a stress controlled DMA

Constant inputs and outputs function as in the TMA A sine wave current is added to the force coil The resultant sine wave voltage of the LVDT is compared to the sine wave force The amplitude of the LVDT is related to the storage modulus, E' via the spring constant, k. The phase lag, , is related to the E" via the damping constant, D.

YOUNG MODULUS OF SOME COMMON POLYMERS Below is the list of some of the commonly used polymers describing their Youngs Modulus with respect to the densities:PolymerDensity(kg/m3)Tensile Strength(N/mm2)Elongation (%)Young's Modulus(GPa)

PVC1330482003.4

Polystyrene10504833.4

PTFE2100131000.3

Polypropylene90027200-7001.3

Nylon116060902.4

Cellulose Nitrate135048401.4

Cellulose Acetate13004010-601.4

Acrylic (Methacrylate)11907463.0

Polyethylene95020-3020-1000.7

Epoxy resin, glass filled1600-200068-200420

Melamine formaldehyde, fabric filled1800-200060-907

Urea formaldehyde, cellulose filled150038-9017-10

Phenol formaldehyde, mica filled1600-190038-500.517-35

Acetals, glass filled160058-752-77

DEFINITIONS:YOUNGS MODULUS: Its the ratio between the stress and strain applied on the body within is elastic limit on the stress-strain curves. It is used to compare various materials and make structural calculations and it also the tensile modulus measures a resins stiffness. The higher values of modulus indicate greater stiffness.

LOSS MODULUS:The energy dissipated as heat from the body, representing the viscous portion is measured in term of Loss Modulus. The loss modulus can be calculated as follows:Loss Modulus: Where is the Stress applied is the Strain observed is phase lag between stress and strain.STORAGE MODULUS:The stored energy in a body, representing the elastic portion is measured in terms of the Storage Modulus. The relation can be shown as below:Storage Modulus: Whereis the Stress applied is the Strain observed is phase lag between stress and strain.TAN (DELTA):Tan is a basic parameter used for expressing the energy losses relative to the energy stored. Losses in various dynamic test methods, such as, rebound experiments or decay of free vibrations, can all be expressed in terms of tan . It can be expressed as Tan = E/ EAnd in the shear mode, this equation can be also written as:Tan = G/ G

Figure: A typical DMA plot showing Storage modulus (G), Loss modulus (G) andTan delta () for a typical polymerTOUGHNESS:The ability of a metal to deform plastically and to absorb energy in the process before fracture is termed toughness. The toughness can be measured by calculating the area under the stress strain curve. The unit of toughness is energy per unit volume.

Toughness of the material can be influenced by the below mentioned factors: Strain rate (rate of loading) Temperature Notch effectEXPERIMENTAL: MATERIALS DMA Q 8000 Equipment Polypropylene Polyethylene Teraphthalate METHODThe specimen were clamped in the DMA with suitable clamp and stress was applied to measure the respective deformation which resulted in the stress-strain curves. From these curves, we concluded Young's Modulus, Ultimate Stress, Yield Point, Proportionality Limit, Elastic Limit and Toughness values. These values help to decide about polymers mechanical proporties (ductile, brittle or rubber-like).

RESULTS:GraphsThe Stress-Strain curves resulting from the DMA of PET and PP were obtained as below.

The Stress-Strain Curve was used to calculate the properties of the specimen. The concept of extraction of properties is as below.

Youngs Modulus: Within the linear portion of the curveYoungs Modulus =Stress / Strain PET:= (0.7904) / (0.1388)= 5.69 MPa

PP:= (5.45) / (0.687)= 7.9 MPa

Ultimate Stress:Ultimate stress at of the specimen from the graph were found as below PET = 11.28 MPa PP = 40.87 MPa

Yield Point Yield points at of the specimen from the graph were found as below PET = 5.67 MPa PP = 29.1 MPa

ProportionalityProportionality limit of the specimen from the graph were found as below PET = 1.59 MPa PP = 21.7 MPa

Elastic LimitElastic limit of the specimen from the graph were found as below PET = 4.23 MPa PP = 24.2 MPa

ToughnessBy calculating the area under the curve of both graphs the toughness of both specimen was found to be around PET = 6.86 PP = 4978CONCLUSION AND DISCUSSIONIn this experiment, mechanical properties were measured through which the values of modulus and stress-strain curves were compared for PP (Polypropylene), PET (polyethylene terephthalate).As seen from the graphs (from stress-strain curves), Specimen elongation can be estimated from curves: Polypropylene is more elongated than PET. It shows that PP is more elastic than PET. Therefore we can say that brittleness of PET is more than PP. In stress-strain diagrams, area under the curve gives toughness value. The area occupied by the PP specimen is very huge than that of PET. It is because PP absorbs more energy than PET. PP sample more flexible than PET because of its higher strain and lower Young's Modulus (E) than PP. Maximum strain value is higher for PP it means that elongation of PP is greater We can conclude the experiment by comparing the stress-strain curves of the specimen and relating them with their chemical structure. We observed that PET has brittle behavior, PP has ductile behavior. Ductile materials have more ultimate strain. This property decrease their Young's Modulus (E) (E=Stress/Strain). Young's Modulus relates with rigidity. So PET is more rigid polymer than PP.

REFERENCES Menard, K. P., Dynamic Mechanical Analysis, Encyclopedia of Polymer Science and Technology, 2004 Dutta, N. K., Thermal Analysis of Rubbers and Rubber Materials, 2010 Miehe, C., Goktepe, S., Diez, J. M., Finite viscoelasticity of amorphous glassy polymers- in the logarithmic strain space, International Journal of Solids and Structures, 45(2009), 181-202 Neil Drake, Specialty and High Performance Rubbers, Rapra Technology Limited,1997

SUMMARY (ARTICLE):TENSILE AND FRACTURE BEHAVIOUR OF PP/WOOD FLOUR COMPOSITESEzequiel Prez, Luca Fam, S.G. Pardo, M.J. Abad, Celina Bernal,Natural fiber reinforced composites have gained a lot of importance due to their light weight, adequate strength and stiffness, and low cost. They can also be made out by using the conventional plastic processing techniques. The usage of natural fibers as a reinforcement has good advantages but their potential as a reinforcement is reduced due to their incompatibility with the hydrophobic polymer matrix, their poor resistance to moisture and their tendency to form aggregates during processing. Thats why different additives are added to react with the fiber and matrix to provide the best optimized solution. Polypropylene is a common polymer with good mechanical properties and lower cost. It can blend with variety of composites to produce wide range of applications. Natural fiber reinforced PP composites are well known in the automotive and building industries. These applications require fracture toughness also in parallel to High stiffness and thickness. In this paper the author had worked with PP/Wood composites with the addition of grafting of maleic anhydride on PP to observe the tensile and fracture behavior. Samples of composite were prepared with different concentrations of the fiber content and using PP and Wood flour along with Maleic anhydride. Composite plaques of 3mm were compressed molded at 190oC under 50 bar pressure for 10 min. Figures below shows typical tensile stressstrain curves for the PP matrix and the PP/WF composites with different fiber content without and with MAPP, respectively. It can be observed from the first Fig that most materials displayed plastic deformation beyond maximum load with some drop of load to zero at a certain point in the stressstrain curve. The increase in fiber content increased the brittle behavior.

Typical loaddisplacement curves for fracturing samples with different combinations of fiber and coupling agent are given in below.

Most of the specimen resulted in quasi-brittle fracture behavior which can be observed by non-linear loaddisplacement curves with a certain drop of load to zero before maximum load or around this point. In addition, macroscopically, none of the samples exhibited plastic damage during the tests.The addition of fibrous content in the composites added reliable fracture toughness in PP/ WF composites. They are useful for design purposes when these composites are used in structural applications. Youngs modulus was also increased with the addition of wood flour to PP as expected, whereas tensile strength, strain at break and fracture toughness were found to decrease as fiber content increased. The presence of MAPP added tensile strength and ductility and had no significant effect on fracture toughness.From this research it can be concluded that although ductility and toughness were reduced for the composites with respect to PP, but sustainable stiffer materials were obtained by using MAPP as a coupling agent. These materials are significant and bio-degradable whereas PP is non-biodegradable material (PP) and they also give a cost saving without losing strength.

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