Thermal behaviour of polymers

The melting of polymer crystals exhibits many instructive features of non-equilibrium behaviour. It has been known since the 1950s that the crystals of flexible-chain polymers, e.g. polyethylene (PE), are lamella-shaped with the chain axis almost parallel to the normal of the lamella. The lamellar thickness (LJ is of the order of 10 nm, corresponding to approximately 100 main chain atoms, which is considerably less than the total length of the typical polymer chain. This fact led to the postulate that the macroconformation of the chains must be folded. The 

Extended-chain crystals of polyethylene are produced by high-pressure crystallization at elevated temperatures, typically at 0.5 MPa and 245 °C. These micrometre-thick crystals display a distinctly different melting behaviour from that of the thin folded-chain single crystals grown from solution. The recorded 

The lamellar shape LJVsf 0.01-0.001, where W is the width of the crystal) of the polymer crystals is the reason for the rearrangement occurring at 

The content of the crystalline component, the crystallinity, in semicrystalline polymers is a major factor affecting their material properties, e.g. modulus, permeability and density. The crystallinity of a sample 

The mass crystallinity wj obtained from the heat of fusion is based on the measurement of the area under the DSC melting peak. The choice of base line is crucial, particularly for polymers of low crystallinity, e.g. poly(ethylene terephthalate) (PETP). Another problem arises from the fact that the heat of fusion is temperature-dependent. What temperature should 

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The presence of a comonomer can deeply affect the thermal behaviour of polymers. A comonomer can in some cases confer stability but in others may render a homopolymer unstable. Some important systems will now be described and discussed a review on the subject has been published by Grassie [304]. 

C. Vasile, E. M. CSlugSru, A. Stoleriu, M. Sabliovschi and E. Mihai, Thermal Behaviour of Polymers (in Romanian), Ed. Academiei, Bucharest, 1980. 

C Vasile, EM Calugaru, A Stoleru, M Sabliovschi, E Mihai. Thermal Behaviour of Polymers, Bucharest Ed. Academiei, 1980, pp 167-190. 

R. Antony, Synthesis, Characterization and Thermal Behaviour of Chemically Modified Phenolic and Substituted Phenolic Polymers, Ph.D thesis. Regional Research Laboratory, Trivandrum and Kerala University, Trivandrum, India (1993). 

Zanetti, M., Camino, G., Thomann, R. and Mulhaupt, R. 2001. Synthesis and thermal behaviour of layered silicate-EVA nanocomposites. Polymer 42 4501- 4507. 

Nicholson, J. W., Wasson, E. A. Wilson, A. D. (1988). Thermal behaviour of films of partially neutralised poly(acrylic acid). 3. Effect of calcium and magnesium ions. British Polymer Journal, 20, 97-101. 

Pyrolysis-MS, together with TGA analysis, was chosen recently as the technique with which to investigate the thermal behaviour of two polythiophene copolymers, since insolubility in common solvents of conducting polymers limits... 

Let us consider some aspects of thermal behaviour of LC polymers 45> (Fig. 3). In case of crystallizable polymers, which are mainly those containing mesogenic groups in the main chain, the LC state is observed from above the melting temperature (Tm) and up to the clearing temperature (Tcl), the melt displays anisotropy and may flow. The polymer thus behaves alike low molecular liquid crystals (Fig. 3 a), the viscosity of the former being, however, essentially higher. 

Thermal analysis is a group of techniques in which a physical property of a substance is measured as a function of temperature when the sample is subjected to a controlled temperature program. Single techniques, such as thermogravimetry (TG), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric thermal analysis, etc., provide important information on the thermal behaviour of materials. However, for polymer characterisation, for instance in case of degradation, further analysis is required, particularly because all of the techniques listed above mainly describe materials only from a physical point of view. A hyphenated thermal analyser is a powerful tool to yield the much-needed additional chemical information. In this paper we will concentrate on simultaneous thermogravimetric techniques. 

Barton JM, Hamerton I, Rose JB, Warner D (1991) A comparative study of the thermal behaviour of some aryl bismaleimides and biscirtraconimides. In Abadie MJM., Sillion B (eds) Polyimides and other high temperature polymers (Proceeding of the 2nd European Technical Symposium on Polyimides and High Temperature Polymers, STEPI 2). Elsevier, Amsterdam, p 283... 

Costa, L. Goberti, P. Paganetto, G. Camino, G. Sgarzi, P Thermal behaviour of chlorine-antimony fire-retardant systems, Polymer Degradation and Stability, 1990, 30(1), 13-28. 

Price, D., Cunliffe, L. K., Bullett, K. J., Hull, T. R., Milnes, G. J., Ebdon, J. R., Hunt, B. J., and Joseph, R, Thermal behaviour of covalently bonded phosphate and phosphonate flame retardant polystyrene systems, Polym. Degrad. Stab., 2007, 92, 1101-1114. 

Gao, F., Tong, L., and Fang, Z. 2006. Effect of a novel phosphorous-nitrogen containing intumescent flame retardant on the fire retardancy and the thermal behaviour of poly(butylene terephthalate). Polym. Deg. Stab. 91 1295-1299. 

B.N. Jang, M. Costache, and C.A. Wilkie, The relationship between thermal degradation behaviour of polymer and the fire retardancy of polymer/clay composites, Polymer, 2005, 46 10678-10687. 

The thermal behaviour of this polymer was investigated by Lenz (1985), who found the following experimental values Tk = 500 K and Tj = 563 K (in reasonable agreement). 

Eq. (13.37) shows that the modulus of a rubber increases with temperature this is in contrast with the behaviour of polymers that are not cross-linked. The reason of this behaviour is that rubber elasticity is an entropy elasticity in contrast with the energy elasticity in "normal" solids the modulus increases with temperature because of the increased thermal or Brownian motion, which causes the stretched molecular segments to tug at their "anchor points" and try to assume a more probable coiled-up shape. 

The properties which determine the "environmental behaviour" of polymers after processing into final products may be divided into three categories the thermal end use properties, the flammability, and the properties determining the resistance of polymers to decay in liquids. 

The thermal behaviour of copolymers (113) with pendant phosphazene groups, prepared by copolymerization of [NP(OPh)2]NP(OPh)[OC6H3(OH)2-3,5], C6H4(0H)2-1,3 and OCN(CH2)6NCO, have been investigated. An enhancement of the char yield has been observed with increasing phosphazene content. The related cyclolinear polymer will be discussed in Section 4. 

As a final consideration, it is relevant to discuss the behaviour of mixtures of different plastics. In fact, one possible process for recovering valuable chemical and petrochemical products from plastic waste is the stepwise thermal degradation of polymer mixtures. This potentially allows the step-by-step simultaneous separation of the different fractions generated by the polymers of the blend. The effect of the mixing scale of PE and PS and their interactions in the melt on the basis of several hypotheses was recently investigated (Faravelli et al., 2003). The first and simplest approach was a completely segregated model which... 

In this section the mechanism of PTFE degradation will be outlined, but since kinetic data on the other fluorinated polymers are very scarce, we shall only characterize their stability by thermogravimetric data (Table 12 and Figs. 65—67). Comprehensive reviews on the thermal behaviour of fluorinated polymers have been published by Wright [242, 243] and Wall [244]. 

Fig. 65. Weight loss behaviour of polymers representing several degradation processes and a wide range of thermal stabilities. The curves show volatilization rates of polymers heated in nitrogen at atmospheric pressure and at a constant rate of temperature increase of 100 degC h 1 [242].

Polyhexafluoropropene and polyperfluorohept-l-ene have low thermal stability (Table 12). Perfluoroacenaphthylene polymer is not more stable than polytrichlorofluoroethylene [243, 260]. Perfluorobutyne-2 yields i highly branched and crosslinked material which is more stable than PTFE [261]. Perfluorallene also gives a highly crosslinked solid, the thermal behaviour of which has not been characterized [262]. 

We will discuss in this section the various ways that can be used to improve the thermal stability of polymers. The synthesis and thermal behaviour of some typical heat-resistant polymers (sometimes commercially available) will then be given. The volatilization of these materials has very seldom been thoroughly studied orders of reaction, activation energies and pre-exponential factors have generally not been determined. Therefore the thermal stability of the polymers will be characterized in an arbitrary way for the purpose of comparison. It must be stressed, however, that the physical properties of a polymer are at least as important for use at high temperature as the volatilization characteristics an infusible polymer is very difficult to process, and a heat resistant polymer with a low softening temperature is often useless. The softening temperature corresponds to the loss of mechanical properties. It can be measured by the standard heat deflection test. 

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