Thermal distortion temperature

Polymer/clay nanocomposites were first prepared by Carter, Hendricks, and Bolley (1950), bnt only at the end of the 1980s was there the development of a great tnrning point in the polymer-clay nanocomposite technology by Toyota, using polyamide 6 and organophilic clays especially prepared for this nanocomposite (Kawasnmi et al., 1989 Okada et al., 1988). They developed this nanocomposite to be applied in timing belt covers of Toyota vehicles, in collaboration with the UBE Indnstries, a Japanese polyamide 6 indnstry. This nanocomposite had only 5 wt% special clay, which sensibly improved the final material properties as compared with pnre polyamide 6. The nanocomposite formation provided an increase of 40% in the rnptnre tension, 60% of the tensile modnlns, and 126% in the flexion modulus, in addition to the increase in the thermal distortion temperature from 65 to 152°C as compared to the pure polymer. 

The hydroxyl content of commercial material is kept low but it is to be observed that this has an effect on the water absorption. Variation in the residual acetate content has a significant effect on heat distortion temperature, impact strength and water absorption. The incorporation of plasticisers has the usual influence on mechanical and thermal properties. 

It has already been shown (e.g. Chapters 20 and 21) that the insertion of a p-phenylene into the main chain of a linear polymer increased the chain stiffness and raised the heat distortion temperature. In many instances it also improved the resistance to thermal degradation. One of the first polymers to exploit this concept commercially was poly(ethylene terephthalate) but it was developed more with the polycarbonates, polysulphone, poly(phenylene sulphides) and aromatic polyketones. 

The thermal properties of the resin are dependent on the degree of cross-linking, the flexibility of the resin molecule and the flexibility of the hardener molecule. Consequently the rigid structures obtained by using cycloaliphatic resins or hardeners such as pyromellitic dianhydride will raise the heat distortion temperatures. 

Resin Material Compressive Modulus, psi x 103 Heat Distortion Temperature, °F, 264 psi Heat Resistance, Continuous °F Thermal Expansion, in./in.- C x 10-5 Thermal Conductivity, cal/cm2-sec-°C-cm x 10 4 Volume Resistivity, ohm-cm... 

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)... 

Nylon-6-clay nanocomposites were also prepared by melt intercalation process [49]. Mechanical and thermal testing revealed that the properties of Nylon-6-clay nanocomposites are superior to Nylon. The tensile strength, flexural strength, and notched Izod impact strength are similar for both melt intercalation and in sim polymerization methods. However, the heat distortion temperature is low (112°C) for melt intercalated Nylon-6-nanocomposite, compared to 152°C for nanocomposite prepared via in situ polymerization [33]. 

Polyesters exhibit excellent physical properties. They have high tensile strength, high modulus, they maintain excellent tensile properties at elevated temperatures, and have a high heat distortion temperature. They are thermally stable, have low gas permeability and low electrical conductivity. For these reasons, polyesters are considered engineering polymers. 

Typically, polyester resins are used for high-end applications that require excellent electrical and thermal resistance. When dimensional stability under load is more critical, glass fibers are incorporated to increase the heat distortion temperature and the stiffness of the part. Examples of glass fiber reinforced parts include electrical housings, electrical adapters, computer components, telephone housings, and light bulb sockets. When impact modified, polybutylene terephthalate can be injection molded to make car bumpers. 

Polyethers. Acetal Resins. These stabilized polyoxymethy-lenes were introduced dramatically by DuPont and Celanese as engineering plastics to replace non-ferrous metals. Good mechanical strength, resilience, fatigue-resistance, lubricity, abrasion-resistance, heat distortion temperature, water and solvent-resistance can approach the behavior of metals on a volume basis, while processability, color possibilities, and corrosion-resistance are superior. Major weakness is sensitivity to thermal, oxidative, and ionic degradation. 

Polysulfone Plastics. These plastics which were commercialized by Union Carbide are actually aromatic polyethers containing periodic sulfone groups which provide additional resonance stabilization. They have good mechanical properties, creep resistance, and dimensional stability but their outstanding quality is their high heat distortion temperature (345°F.) and resistance to thermal oxidative degradation. Limitations are difficult thermoplastic processability, amber color, and sensitivity to organic solvents. 

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. 

Compared with other catalysts that homopolymerize epoxies, the imidazole offers improved thermal properties and retention of mechanical properties at more elevated temperatures. The cured resin has a heat distortion temperature between 85 and 130°C, which can be further increased by a postcure to about 160°C. 

Hybrid resins have been used to improve the flexibility, thermal shock resistance, elongation, heat distortion temperature, and impact strength of unmodified epoxy adhesives. However, there can also be some sacrifice in certain physical properties due to the characteristics of the additive. These alloys result in a balance of properties, and they almost never result in the combination of only the beneficial properties from each component without carrying along some of their downside. 

Heat Distortion Test. Two remaining bars from the cleavage tests are used to determine heat distortion temperature in accordance with ASTM D-621 test methods. These thermal-mechanical tests are necessary to determine whether a brittle resin has been truly toughened or whether it has been merely flexibilized. The morphology of the resin also effectively describes a true toughening situation and can aid immeasurably in explaining departures from true toughening. 

Effect of Level of CTBN. In Table V we varied the level of CTBN at a constant amount of piperidine. At 20 parts of CTBN we find a fourfold increase in impact strength with an 11 °C loss of heat distortion temperature. This loss of thermal properties suggests that some of the CTBN flexibilizes the epoxy matrix. The morphology of these systems all shows about the same particle size. However electron micrographs of the fracture surface of the system with 20 parts CTBN show that the particles are somewhat larger and more diffuse. 

It is interesting that the polystyrene produced by suspension polymerization, particularly the Koppers material, had a heat distortion temperature superior to that of the Dow polystyrene [6]. This was attributed to the measurable levels of residual dimers and trimers in the Dow product due to its thermal initiation and which were absent in the peroxide-initiated suspension process. 

Fillers reduce shrinkage of polymer foams. Mica and glass fiber reduce warpage and increase the heat distortion temperature. Intumescent fillers increase in volume rapidly as they degrade thermally expanding the material and blocking fire spread. 

Mechanical perfoimance (tensile, flexural, impact, bursting pressure, and compressive strength), resistance to heat, thermal expansion coefficient, heat distortion temperature, maximum working temperature, burning class, UV stability, and working stress are the most important parameters characterizing performance requirements of pipes and hoses and are used as selection criteria. Fillers can help to fulfill these requirements, but are underutilized. Fillers seem mainly to be used to lower cost. 

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