Heat distortion temperature , glass transition

Many different methods can be used to measure the degree of crosslinking within an epoxy specimen. These methods include chemical analysis and infrared and near infrared spectroscopy. They measure the extent to which the epoxy groups are consumed. Other methods are based on the measurements of properties that are directly or indirectly related to the extent and nature of crosslinks. These properties are the heat distortion temperature, glass transition temperature, hardness, electrical resistivity, degree of solvent swelling and dynamic mechanical properties, and thermal expansion rate. The methods of measurement are described in Chap. 20. 

TDI isomers, 210 Tear strength tests, 242-243 TEDA. See Triethylene diamine (TEDA) Telechelic oligomers, 456, 457 copolymerization of, 453-454 Telechelics, from polybutadiene, 456-459 TEM technique, 163-164 Temperature, polyamide shear modulus and, 138. See also /3-transition temperature (7)>) Brill temperature Deblocking temperatures //-transition temperature (Ty) Glass transition temperature (7) ) Heat deflection temperature (HDT) Heat distortion temperature (HDT) High-temperature entries Low-temperature entries Melting temperature (Fm) Modulu s - temperature relationship Thermal entries Tensile strength, 3, 242 TEOS. See Tetraethoxysilane (TEOS)... 

Except for a lew thermoset materials, most plastics soften at some temperatures, At the softening or heat distortion temperature, plastics become easily deformahle and tend to lose their shape and deform quickly under a Load. Above the heat distortion temperature, rigid amorphous plastics become useless as structural materials. Thus the heat distortion test, which defines The approximate upper temperature at which the material can be Safely used, is an important test (4,5.7.24). As expected, lor amorphous materials the heat distortion temperature is closely related to the glass transition temperature, hut tor highly crystalline polymers the heat distortion temperature is generally considerably higher than the glass transition temperature. Fillers also often raise the heat distortion test well above... 

The heat distortion temperature of impact-resistant polystyrene may also be improved by polymer blends. Those of impact-resistant polystyrene with poly-2,5-dimethylphenylene-1,4-oxide (PPO) are particularly interesting (90). Polystyrene and PPO are molecularly compatible and mixtures of them have glass transition temperatures which vary virtually linearly with composition. A further advantage of these compositions which should not be under-estimated is their better flame resistance. 

It was also found that the tensile heat distortion temperatures of films containing only a few mole per cent of these units were considerably higher than those found for bisphenol A polycarbonate. X-ray diffraction studies made on the test samples used in the tensile heat distortion apparatus could not demonstrate an increase in crystallinity of the samples. Only a slight indication of increase of orientation was apparent. Glass transition temperatures measured by the refracto-metric method were considerably lower than the heat distortion temperatures. 

The heat-distortion temperatures in the tables are the temperatures at which the films distorted 2% while under a load of 50 p.s.i. Except for examples in which the antiplasticizer concentration was 40 to 50%, the heat-distortion temperatures were usually within 10°C. of the glass transition temperatures, which are the temperatures at which the films distorted 0.25% while under a load of 5 p.s.i. Distor-... 

The degree of crosslinking is generally less, leading to a lower glass transition temperature, heat distortion temperature, and chemical resistance. 

Among these, polystyrene is the lowest cost, commodity type resin followed by SAN, SMA and the other copolymers. All the styrenic resins are essentially amorphous polymers with glass transition temperatures ranging from about 100 to 130°C, and heat distortion temperatures ranging from about 80 to 120°C, depending upon the comonomer and impact modifier content. 

PVC, however, suffers from an inherent susceptibility to thermal degradation and hence must invariably be processed with heat stabilizers and careful control of processing temperature. The other important drawbacks of PVC are its brittleness in the absence of a plasticizer (low notched Izod impact strength) and its low heat distortion temperature (ca. 60°C) originating from its low glass transition temperature and essentially... 

The structures and glass transition temperatures of several commercial polysulfones are listed in Table 4.30. The polymers have different degrees of spacing between the p-phenylene groups and thus have a spectrum of glass transition temperatures which determine the heat-distortion temperature (or deflection temperature under load), since the materials are all amorphous. 

The process is slow except at high temperatures. Considering unreinforced resins hrst, absorption causes dimensional changes and softening, that is, a reduction in surface hardness and in modulus. The glass transition temperature and associated heat distortion temperature of the resin fall substantially, lowering the maximum permissible use temperature of the resin [23]. 

The glass-transition temperature, melting point, heat distortion temperature, thermal degradation temperature, ete. are important parameters affecting the application and processing of semicrystalline polymer materials. These thermal parameters can be obtained via differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, etc. 

P(l) The selection of polymer resins for use in structural composites will be determined by a number of factors and should not be made without full consultation with materials suppliers and fabricators. Properties required are usually dominated by strength, stiffness, toughness and durability. Account should be taken of the application, service temperature and environment, method of fabrication, cure conditions and level of properties required. A knowledge of service temperature is required to select an appropriate stable resin system as with all polymers loss of stiffness and significant creep will occur if the service temperature is close to the resin second order glass transition temperature. The latter is related to the heat distortion temperature (HDT). 

Resins with a high heat distortion temperature (HDT) or glass transition temperature (Tg) usually exhibit a greater creep modulus than that of resins with a low HDT or Tg. 

Commercial SMA resins (Xiran , Polyscope Polymers) are amorphous, random copolymers of styrene and maleic anhydride (8-30 %) that exhibit higher glass transition temperatures (20-60 °C higher) and higher heat distortion temperatures than polystyrene. The SMA resins were originally commercialized under the trade name of Dylark by ARCO and by Nova chemicals but later on discontinued. 

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