Thermoplastic articles

Foamed thermoplastic articles have a cellular core with a relatively dense (solid) skin. The foam effect is achieved by the dispersion of inert gas throughout the molten resin directly before moulding. Introduction of the gas is usually carried out either by pre-blending the resin with a chemical blowing agent which releases gas when heated or by direct injection of the gas (usually nitrogen). 

In summary, the final properties of thermoplastic articles depend both on the molecular structure of the polymer and on the details of the fabrication operations. This is a disadvantage, in one sense, since it makes product design more complicated than with other materials that are less history-dependent. On the other hand, this feature confers an important advantage on plastics because fabrication particulars are additional parameters that can be exploited to vary the costs or balance of properties of the products. 

A method of bonding thermoplastic articles of like materials to each other by using a solvent capable of softening the surfaces to be brmded. Thermoplastic materials that can be bonded by this method are ABS, PA, PC, PS, acrylics, ceUulosics, and vinyls. 

High-frequency welding n. A method of welding thermoplastic articles in which the surfaces to be joined are heated by contact with electrodes of a high-frequency electrical generator. 

Solvent polishing n. A method for improving the gloss of thermoplastic articles by immersion in, or spraying with a solvent... 

Impact-resistant properties, especially at low temperatures, low-temperature toughness, melt-processing properties, and dimensional stability of thermoplastic polyurethane elastomers are improved by the addition of a carbonyl-modified polyolefin [54,55]. These improvements are particularly useful for reinforced polyurethanes. Small amounts of polyolefin homopolymer or copolymer with TPU blends are useful for molding plastic articles by injection molding, extrusion, calendering, or similar process for molding thermoplastic articles [56]. 

Such nonrectangular sections are common in many thermoplastics articles. Channels, T-sections, and hollow comer pillars are found in many parts, such as crates and stacking containers, and inverted U-sections and cantilevers are common in items such as streetlamp housings and aircraft. 

Solvent Polish ng m A method for improving the gloss of thermoplastic articles by immersion in, or spraying with a solvent that will dissolve surface irregularities, followed by evaporation of the solvent. The method is used primarily for cellulosics, for which dipping is suitable. Plastics that are subject to crazing, such as polystyrene, are usually sprayed rather than dipped. 

Wyeth NC, Roseveare RN. Process for producing biaxially oriented thermoplastic article. US Patent No. 3,849,530 issued November 19,1974. 

Environmental stress cracking The susceptibility of a thermoplastic article to crack or craze formation under the influence of certain chemicals and stress. 

Natural mbber is a classic example of the difference between a thermoplastic and a thermoset. Introduced to Europe by Columbus, natural rabber did not achieve commercial significance for centuries because it was a thermoplastic, articles madeof it would become soft and sticky on hot days. In 1839, Charles Goodyear discovered the curing reaction with sulfur (which he called vulcanization in honor of the Roman god of fire) that converted the polymer to a thermoset. This allowed the rubber to maintain its useful properties to much higher temperatures, which ultimately led to its great commercial importance. 

Winicov et al. [84] reported the use of Pluronic polyols as lubricants for conveyor systems that handle thermoplastic articles. Many aqueous lubricants can adversely affect certain types of materials such as polyethylene terephthal-ate (PET), polybutylene terephthalate (PBT), polycarbonate, etc. The authors reported that lubricants made with Pluronic F-108 showed marked superiority over other commercially available lubricants with regard to lubricity and... 

---