Thermoplastic materials material selection

This book focuses on the relationships between the chemical structure and the related physical characteristics of plastics, which determine appropriate material selection, design, and processing of plastic parts. The book also contains an in-depth presentation of the structure-property relationships of a wide range of plastics, including thermoplastics, thermosets, elastomers, and blends. 

The function of the resin matrix material in filament-wound structures is to help distribute the load, maintain proper fiber position, control composite mechanical and chemical properties, and provide interlaminar shear strength. Either a thermosetting or a thermoplastic resin material may be selected. Thermosetting resins may be selected for application in a wetwinding process or as part of a prepreg resin system. 

A decrease in thermal diffusivity, with increasing temperature, is also observed in semicrystalline thermoplastics. These materials show a minimum at the melting temperature as demonstrated in Fig. 2.18 [24] for a selected number of semi-crystalline thermoplastics. It has also been observed that the thermal diffusivity increases with increasing degree of crystallinity and that it depends on the rate of crystalline growth, hence, on the cooling speed. 

Table 3 shows the Tg values and solubility of some selected polyimides among those prepared from monomers of Tables 1 and 2. The combination of non-pla-nar dianhydrides and non-planar, raefa-oriented aromatic diamines containing flexible linkages provides the structural elements needed for solubility and melt processability. Some aromatic polyimides marketed as thermoplastic materials are based on these statements [9,57-60]. 

This research project represents initial studies into a new approach to blending thermoplastic materials like polystyrene with wood materials, leading to a new class of wood-plastic composites. Traditional wood-plastic composites have involved the impregnation and subsequent in situ polymerization of vinyl monomers. This procedure has been adopted for selected products for which improved physical properties justify increased production costs. While producing mixtures or blends of wood and plastics, these types of composites do not demonstrate significant chemical bonding between the wood and plastic components. 

MATERIALS. Selection of a base polymer thermoplastic resin from which a molded substrate is produced is influenced by factors of price and performance. Secondary considerations include supplier preference. Given the uniqueness of each product application, standardization of generic polymers is unlikely. In fact, the selection possibilities are likely to grow with continued diversification of application requirements/specifications. 

The information is limited to the most important materials, metals, plastics, (thermoplastics, thermoset materials, foams), ceramics, glass and their possible combinations. For papers, cardboards, wood, rubber polymers, usually physically setting systems (solvent-based, dispersion, hot-melt adhesives) are utilized. In these cases, the adhesive selection with regard to the manufacturing conditions and demands is of less problematic nature. 

There are no standard test methods specific for discontinuous fiber (or short fiber) reinforced thermoplastics. It is also not clear whether a geometry-independent fracture parameter can be measured for these nonuniformly inhomogeneous materials. However in spite of these reservations there has been considerable work conducted towards characterizing short fiber composites for fracture toughness using the standard and other procedures outlined in the previous sections. The investigators have recognized that fracture mechanics data provide much more reliable information than the customary alternative tests for material selection and also a service performance indicator for components. 

A second critical formulation area is the use of selective, reactive tougheners in combination with thermoset polymers, which results in a highly toughened adhesive that does not sacrifice mechanical properties. These avenues are far superior to the traditional method of softening the polymer matrix with thermoplastic materials that will degrade mechanical properties. Further development in this area continues. 

Here an isotactic polypropylene matrix (iPP) was selected as an example because thermoplastics are materials with a higher consumption due to their well-balanced physical and mechanical properties and their easy processability at a relatively low cost that makes them a versatile material. ... 

The four major thermoplastics—polyethylene, polypropylene, PVC, and polystyrene—together represent over 85% by volume of world plastics consumption. Because of their lower prices, these commodity materials dominate the market, and in any materials selection procedure there are good economic reasons for considering them first before turning to the more expensive engineering plastics. 

It is hoped that the following sections will be of value to researchers in science and engineering and to clinical practitioners who are engaged in the development and material selection of new thermoplastic polymers for biomedical applications. 

Figure 23.47 A selection of carbon fiber thermoplastic components, (a) Carbon fiber reinforced APC thermoplastic aircraft floorpanel (EH101 Merlin) Makes use of improved toughness and damage tolerance of thermoplastic materials, (b) Bulkhead or wing stiffener made from carbon fiber/PEEK thermoplastic Made in one piece apart from the ring stiffener, (c) Underslung carbon fiber APC2 reinforced thermoplastic tailplane. This item was made over 10 years ago and was the largest piece of flying thermoplastic in the world Fins are fabricated from Ultem 1000 (PEI). Source Courtesy of GKN.

Polymeric materials are used in a vast array of products. In the automotive area, they are used for interior parts and in under-the-hood applications. Packaging applications are a large area for thermoplastics, from carbonated beverage bottles to plastic wrap. Application requirements vary widely but, luckily, plastic materials can be synthesized to meet these varied service conditions. It remains the job of the part designer to select from the array of thermoplastic materials available to meet the required demands. 

Nevertheless, many elastomers and plastics are fundamentally very similar. Most plastics and elastomers comprise long chains of one or more types of linked monomer units. In fact, many of the same monomers are found in both thermoplastic and elastomeric polymers—e.g., styrene, acrylonitrile, ethylene, propylene, and acrylate esters. Because of the chemical similarities between elastomers and plastics, these materials are susceptible to many of the same types of chemical attack. Therefore, many of the same material-selection principles come into play for both plastics and elastomers. 

Any chemical compound that, when added to thermoplastic material, selectively absorbs ultraviolet rays. Process in which surfaces are thinly coated with metal by exposing them to the vapor of metal that has been evaporated under vacuum (one millionth of normal atmospheric pressure). 

Process selection is simplified because the process of choice for most bottle cap applications is injection molding. Compression and transfer molding are possibilities, however, they are slower than injection molding and are rarely used for thermoplastic materials. Therefore, they would only be considered if the material of choice turned out to be a thermoset. 

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