Properties Dimensional Stability

Specifications, Standards, Quality Control, and Health and Safety Factors. Formerly, there was an Insulation Board Institute representing the insulation board industry, but the decline in the market and number of producers has led to its demise. Currendy (ca 1997), the industry is represented by the American Hardboard Association (AHA). Specifications and standards are found in American National Standards Institute (ANSI) standard for CellulosicFiberboard (7). The standard includes descriptions of the various types and classes of fiberboard, as well as requirements for physical and dimensional stability properties. Quality control tests are limited to a few basic strength and stability tests, including bending strength, bond strength, and moisture resistance. 

The excellent balances of mechanical, electrical, solvent resistance, heat resistance and dimensional stability properties combined with a relatively low price have led to the common use of this material in engineering plastics. 

Although regenerated cellulose plants still exist, worldwide usage has significantly reduced due to the better dimensional stability properties of various polypropylene-based films. However, regenerated cellulose still finds usage for certain special applications, e.g. overwraps. 

Various sensors for temperatures, air flow, etc., all require exceptional dimensional stability, property retention at elevated temperatures, fluid resistance and creep resistance. Ignition components require many similar properties but have the additional need for good electrical properties, i.e., high dielectric strength, and good adhesion to epoxy potting compounds. Materials that see these applications include PBT/PC and PPE/HIPS. 

The 1950s also saw the development of two families of plastics — acetal and polycarbonates. Together with nylon, phenoxy, polyimide, poly(phenylene oxide), and polysulfone they belong to the group of plastics known as the engineering thermoplastics. They have outstanding impact strength and thermal and dimensional stability — properties that place them in direct competition with more conventional materials like metals. 

Chem. Descrip. Triphenyl phosphite CAS 101-02-0 EINECS/ELINCS 202-908-4 Uses Costabilizer for PVC and other polymers such as PP vise, modifier, reactive diluent for a variety of resin systems, esp. epoxies antioxidant for syn. rubbers, butyrates flame retardant for PU foams in transesterification reactions lubricant oil additive chem. intermediate for prod, of other phosphite esters and phosphonates Features Improves adhesion, elec, props., dimensional stability Properties Colorless mobile liq. 10% P Albrite Tributyl Phosphate [Huntsman Surf. Sciences]... 

Polyamide-imides and polyimides have very good electrical properties although not as good as those of the fluorocarbons. However, they are much better than fluorocarbons in mechanical and dimensional stability properties. 

Syndiotactic polystyrene (sPS) is a relatively new material discovery in semicrystalline pol5nners with a high melting point and rapid crystallization rate, which makes it possible to injection mold the material. The stereospecific polymerization was made possible by the combination of a transition metal catalyst with weakly coordinating cocatalysts, such as methylaluminoxane. The excellent balance of mechanical, electrical, solvent resistance, and dimensional stability properties combined with a relatively low price (based on styrene monomer) have made this material a competitor to existing engineering plastics. The products also have excellent heat performance and are finding application in antomotive (under the hood), electrical, and electronic connector systems. 

This section is devoted to describing the chemistry of vinylester resins (including polymerization reactions) along with their mechanical, thermal and chemical (corrosion resistance and dimensional stability) properties. In general, vinylester resins are deemed to combine the best properties of epoxies and unsaturated polyesters in particular, they are easily handled at room temperature, and offer mechanical properties comparable to epoxy resins (Table 4.2). Moreover, they have better chemical resistance than cheaper... 

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. 

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

As already indicated, cellulose acetate is used because of its reasonable toughness, transparency and wide colour range. It is not suitable when good electrical insulation properties, heat resistance, weathering resistance, chemical resistance and dimensional stability are important. 

The properties of the polyurethane moulding compositions are also very similar to nylon 66. The greatest difference in properties is in water absorption, the 6,4-polyurethane absorbing only about of that of nylon 66 under comparable conditions. This results in better dimensional stability and a good retention of electrical insulation properties in conditions of high humidity. Resistance to sulphuric acid is somewhat bettter than with nylon 66 but both types of polymer are dissolved by phenols and formic acid. 

Modifications of the wood surface can be performed by various physical, mechanical and chemical treatments. Chemical treatments especially are performed in order to enhance the dimensional stability, but also for amelioration of physical and mechanical properties or a higher resistance against physical, chemical and biological degradation. 

Liquid crystal polymers (LCP) are a recent arrival on the plastics materials scene. They have outstanding dimensional stability, high strength, stiffness, toughness and chemical resistance all combined with ease of processing. LCPs are based on thermoplastic aromatic polyesters and they have a highly ordered structure even in the molten state. When these materials are subjected to stress the molecular chains slide over one another but the ordered structure is retained. It is the retention of the highly crystalline structure which imparts the exceptional properties to LCPs. 

Typical applications for nylon include small gears, bearings, bushes, sprockets, housings for power tools, terminal blocks and slide rollers. An important design consideration is that nylon absorbs moisture which can affect its properties and dimensional stability. Glass reinforcement reduces this problem and produces an extremely strong, impact resistant material. Another major application of nylon is in fibres which are notoriously strong. The density of nylon is about 1100 kg/m. ... 

Weathering. This generally occurs as a result of the combined effect of water absorption and exposure to ultra-violet radiation (u-v). Absorption of water can have a plasticizing action on plastics which increases flexibility but ultimately (on elimination of the water) results in embrittlement, while u-v causes breakdown of the bonds in the polymer chain. The result is general deterioration of physical properties. A loss of colour or clarity (or both) may also occur. Absorption of water reduces dimensional stability of moulded articles. Most thermoplastics, in particular cellulose derivatives, are affected, and also polyethylene, PVC, and nylons. 

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