Thermal properties heat distortion temperature

Since one of the important parts of the design of a dynamically loaded part is concerned with the heat generated by the hysteresis effect, all of the relevant factors concerned with heat transfer from the part should be determined. This includes the thermal properties of the material such as heat capacity, thermal conductivity, heat distortion temperature the surroundings such as the adjoining structures to which heat can be transferred by conduc-... 

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. 

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. 

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. 

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. 

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. 

Blending provides a convenient way of combining the mechanical, physical, or thermal properties of more than one material. One example is the blend of ABS and PVC. The ABS contributes high heat-distortion temperature, toughness, and easy moldability, while the PVC imparts weatherability and flame retardance, as well as reducing the cost of the blend. Applications of the blend include automotive interior trim, luggage shells, and canoes. 

The maximum use temperature is a term coined by the US organization. The Underwriters Laboratory, and it is the maximum temperature at which a polymer can be used continuously, under low stress conditions, with the loss of no more than 50% of the original useful properties (tensile and impact strength, for example, or dielectric strength in the case of cable insulation). For the engineer unfamiliar with plastics, the low values of typical maximum use temperatures can come as a shock. For example, glass-filled nylon 6,6 has a heat distortion temperature of 252°C, but the resin can embrittle as a result of thermal oxidation within 2 h at 250°C. Even at 70°C, embrittlement will still occur within two years [1]. 

Decomposition temperatures, whether sharp or vague, are seldom actually reached in service life. Reinforced composites are preeminently load-bearing materials, and it is their temperature-dependent mechanical properties, such as T, or the closely related heat distortion temperature, that usually determine the maximum use temperature, at least for short or intermediate term use. Strength, yield stress and modulus all decline with increasing temperature, reflecting the increasing mobility of the molecular structure, and unacceptable levels of physical property loss will often occur well before the onset of thermal or thermo-oxidative degradation. 

Silicones appear in various compositions from thin fluids up to polymers that act as elastomers or thermosetting rigid plastomers. Silicones excel in weather durability, water repellency and in electrical and thermal properties. Silicone resins or coatings have heat-distortion temperatures up to 450 C. They are much used in aviation and the space industry as electrical insulation for motors, glue, protective coatings, a premium elastomer or as additives in construction. 

F flow property, MR mold release, impact property, HDT" heat distortion temperature, S stiffness, MRT moisture resistance, DS dimensional stability, M moldability, LW low warpage, TS thermal stability, LWA low water absorption, lubricity, BM blow moldability, CR " chemical resistance, ER environmental resistance, and SC stress cracking. 

The only effects on the thermal properties seen from the incorporation of a fire retardant additive occurs in the case of high-impact polystyrene (HIPS) where, as shown in Table 8.4, the incorporation of a fire retardant leads to a decease in expansion coefficient and, in the case of the polyesters, where the incorporation of a fire retardant produces a small improvement in heat distortion temperature. 

Decabromodiphenyl ether is cost efficient in HIPS but has poor UV stability and is not melt blendable during injection moulding. TBBA is cost efficient and melt blendable in ABS but has low thermal stability, poor impact properties and may not meet UV stability standards. It also lowers heat distortion temperature. 

In general, most fillers increase the heat distortion temperature (HDT) of plastics as a result of increasing modulus and reducing high-temperature creep. Thermoelastic properties such as coefficient of thermal expansion (CTE) are also affected by the presence of fillers and have been modeled through a variety of equations derived from the rule of mixtures [8]. For directional fillers, this property is strongly orientation-dependent, and because of the difference between the CTE of the filler and that of the matrix, internal stresses may lead to undesirable warpage. 

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