Structure of plastics

It is an unfortunate fact that many students and indeed design engineers are reluctant to get involved with plastics because they have an image of complicated materials with structures described by complex chemical formulae. In fact it is not necessary to have a detailed knowledge of the structure of plastics in order to make good use of them. Perfectly acceptable designs are achieved provided one is familiar with their perfonnance characteristics in relation to the proposed service conditions. An awareness of the structure of plastics can assist in understanding why they exhibit a time-dependent response to an applied force, why acrylic is transparent and stiff whereas polyethylene is opaque and flexible, etc., but it is not necessary for one to be an expert... 

In this book no prior knowledge of plastics is assumed. Chapter 1 provides a brief introduction to the structure of plastics and it provides an insight to the way in which their unique structure affects their performance. There is a resume of the main types of plastics which are available. Chapter 2 deals with the mechanical properties of unreinforced and reinforced plastics under the general heading of deformation. The time dependent behaviour of the materials is introduced and simple design procedures are illustrated. Chapter 3 continues the discussion on properties but concentrates on fracture as caused by creep, fatigue and impact. The concepts of fracture mechanics are also introduced for reinforced and unreinforced plastics. 

Characteristic functions and the representative structures of plastics additives providing marketable and durable materials are included in this chapter. Types of additives for plastics used in contact with food are listed in Table 3-1. Similar additives as for PS are used for elastomer-modified plastics forming multilayer systems (blends) and used rather exceptionally in contact with food, such as high-impact polystyrene (HIPS) or acrylonitrile-butadiene-styrene polymer (ABS). Some of the additives, stabilizers in particular, are very reactive and are present in the plastic matrix in a chemically transformed form. 

Another study of foamed polymers uses modern physicochemical methods of structure elucidation of gas-filled polymers and more accurate mathematical descriptioa These studies have considerably contributed to the understanding of the general character of the spatial structure of plastic foams. Thus, quantitative estimations of the effect of each morphological parameter (specific gravity, size and shape of ceUs, type of communication between ceUs, cell distributbn in the bulk, etc.), on the properties of a given material could be made. 

As noted above, the adequate simulation of the cellular structure of plastic foams is very important for the investigation of the relation between structure and properties of foamed plastics. A solution to this problem would allow to establish not... 

Blair, E. A. Structur of Plastic Foams, in Resinography of Cellular Plastics. Philadelphia ASTM 1967, ASTM Special Publ. No. 414, pp. 84... 

The molecular structure of plastics is of two general kinds long molecules, either linear or branched and space-network molecules. 

Biodegradable multiphase systems based on plasticized starch 9.4.1. Structures of plasticized starch-based multiphase systems... 

FIGURE 1.1 Schematic representation of the structure of plastics, showing the three major types of macromolecular arrangements. Approximately 1 000000 times actual size and greatly simplified. (Crystallites can also occur as the result of chain folding.)... 

Figure 4.2. Structure of plastic brick. See text for explanations. [Adapted from Ellingson, R. T., US Patent 7,160,601, Jan. 9,2007.]...

Figure 4.1 shows coimection between a wooden jamb (12) assembly and plastic brick (14) manufactured from composite. Figure 4.2 shows the structure of plastic brick (14) which is composed of cellular PVC core (21), SAN stabilizing layer (22), and non-cellular PVC wear layer (23). This combination was found to be very resilient and scratch-resistant. 

The chemical and physical structure of plastics, and their resulting properties, can be described by the terms constitution, conformation, and configuration. 

---