Dimensional stabilization

It is used in gyroscopes, computer parts, and instruments where lightness, stiffness, and dimensional stability are required. The oxide has a very high melting point and is also used in nuclear work and ceramic applications. 

Key properties of alkyds are dimensional stability, colorability, and arc track resistance. Chemical resistance is generally poor. 

Key properties of cellulose nitrate are good dimensional stability, low water absorption, and toughness. Its disadvantages are its flammability and lack of stability to heat and sunlight. 

Polystyrene is rigid with excellent dimensional stability, has good chemical resistance to aqueous solutions, and is an extremely clear material. 

SAN resins are rigid, hard, transparent thermoplastics which process easily and have good dimensional stability—a combination of properties unique in transparent polymers. 

Dimensional Stability. The wet heat resistance of PVA fiber is indicated by the wet softening temperature (WTS) at which the fiber shrinks to a specified ratio. At one time, the WTS was not more than 95°C for nonacetalized PVA fiber, but improvement of WTS has been achieved by improvement in heat-drawing and -treating techniques other methods proposed include suppression of polymerization temperature of vinyl acetate (36) and employment of alkafi spinning (37). 

Significant piopeities of insulation (Table 1) include tliermal conductivity, fite resistance, and ntiniinal production of toxic gases primarily during combustion. Other criteria include water-vapor permeability, resistance to water absorption, and dimensional stability over prolonged periods of submission to extreme environments. 

Dimensional Stability. Plastics, ia general, are subject to dimensional change at elevated temperature. One important change is the expansion of plastics with increa sing temperature, a process that is also reversible. However, the coefficient of thermal expansion (GTE), measured according to ASTM E831, frequendy is not linear with temperature and may vary depending on the direction in which the sample is tested, that is, samples may not be isotropic (Eig. 7). 

Fibers have been used by humans for thousands of years, but only in the twentieth century has there been such an explosion in fiber types available to the textile manufacturer. The advent of synthetic fibers possessing improved resiliency and dimensional stability has placed natural fibers, particularly cotton (qv), at an ostensible disadvantage. Before synthetics, various means to control the shrinkage, dimensional stability, and smooth-dry performance of cotton had been investigated, but the appearance of synthetics such as polyester has placed a greater sense of urgency on cotton interests to focus on the perceived deficiencies of natural fibers. 

Dimensional Stability. Dimensional stabiHty refers to how a fiber changes length under the influence of load or heat. Conventionally described in terms of fiber shrinkage (ASTM D885-64) at a defined temperature, the term has also come to mean time dependent length change or creep. 

R. M. RoweU and W. B. Banks, Water Kepelkng and Dimensional Stability of Wood, General Technical Report FPL 50, U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, Wise., 1985. 

A recently introduced polycarbonate-based blend offers a low coefficient of thermal expansion. This new thermoplastic is designed for large sheet applications such as doors or siding. Its high dimensional stability will eliminate warping from exposure to varying temperatures. 

In order to become useful dmg delivery devices, biodegradable polymers must be formable into desired shapes of appropriate size, have adequate dimensional stability and appropriate strength-loss characteristics, be completely biodegradable, and be sterilizahle (70). The polymers most often studied for biodegradable dmg delivery applications are carboxylic acid derivatives such as polyamides poly(a-hydroxy acids) such as poly(lactic acid) [26100-51-6] and poly(glycolic acid) [26124-68-5], cross-linked polyesters poly(orthoesters) poly anhydrides and poly(alkyl 2-cyanoacrylates). The relative stabiUty of hydrolytically labile linkages ia these polymers (70) is as follows ... 

Driers are used in the forest products industry to lower the moisture content of the wood product being processed. Drying of dimension lumber gives it dimensional stability. This type of drying is done in steam kilns and is a batch process. No appreciable pollutants are released. 

Glass-reinforced grades of SAN exhibit a modulus several times that of the unfilled polymer and, as with other glass-filled polymers, a reduced coefficient of thermal expansion and lower moulding shrinkage. The materials are thus of interest on account of their high stiffness and dimensional stability. 

An advantage of the matching densities of the two zones or phases is that there is little warping and generally good dimensional stability. 

There has also been some interest in melt blending with polyamides to increase the toughness but at some sacrifice to dimensional stability and moisture resistance. 

Acetal resins find a number of applications in gears, where they come into competition with the nylons. Acetal gears are superior to those made from nylon in fatigue resistance, dimensional stability and stiffness, whereas nylon gears in conditions of average humidity have greater resistance to impact fatigue and abrasion. 

The very low water absorption of bis-phenol A polycarbonates contributes to a high order of dimensional stability. Table 20.6 shows how the water absorption of j in thick samples changes with time and environmental conditions and the consequent influence on dimensions. 

One particular feature of PPO is its exceptional dimensional stability amongst the so-called engineering plastics. It has a low coefficient of thermal expansion, low moulding shrinkage and low water absorption, thus enabling moulding to close tolerances. 

PPO forms one of a group of rigid, heat-resistant, more-or-less selfextinguishing polymers with a good electrical and chemical resistance, low water absorption and very good dimensional stability. This has led to a number of applications in television such as tuner strips, microwave insulation components and transformer housings. The excellent hydrolytic stability has also led to applications in water distribution and water treatment applications such as in pumps, water meters, sprinkler systems and hot water tanks. It is also used in valves of drink vending machines. 

Good dimensional stability (and low moulding shrinkage)—thus allowing the production of mouldings with close dimensional tolerances. 

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