Plastics Fundamentals, Properties, and Testing

As indicated in Chapter 1 of Plastics Fundamentals, Properties, and Testing, the family of polymers is extraordinarily large and varied. There are, however, some fairly broad and basic approaches that can be followed when designing or fabricating a product out of polymers or, more commonly, polymers compounded with other ingredients. The type of fabrication process to be adopted depends on the properties and characteristics of the polymer and on the shape and form of the final product. 

Polyurethane foams, also known as urethane foams or U-foams, are prepared by reacting hydroxyl-terminated compounds called polyols with an isocyanate (see Figure 1.29 of Plastics Fundamentals, Properties, and Testing). Isocyanates in use today include toluene diisocyanate, known as TDI, crude methylenebis(4-phenyl-isocyanate), known as MDI, and different types of blends, such as TDI/crude MDI. Polyols, the other major ingredient of the urethane foam, are active hydrogen-containing compounds, usually polyester diols and polyether diols. 

One-shot processes require sufficiently powerful catalysts to catalyze both the gas evolution and chain extension reaction (Figure 1.29 of Plastics Fundamentals, Properties, and Testing). Use of varying combinations of an organometalUc tin catalyst (such as dibutyltin dilaurate and staimous octoate) with a tertiary amine (such as alkyl morpholines and triethylamine), makes it possible to obtain highly active systems in which foaming and cross-linking reactions could be properly balanced. 

Ester plasticizers (phthalates and phosphates) that are used to plasticize PVC (see Chapter 1 of Plastics Fundamentals, Properties, and Testing) are also used as process aids, particularly with NBR and CR. Polymerizable plasticizers such as ethylene glycol dimethacrylate are particularly useful for peroxide curing rubbers. They act as plasticizers or tackifiers during mixing and undergo polymerization by peroxide initiation during cure. 

The material in this book is included in our well-known Plastics Technology Handbook and it focuses on a wide range of polymers, both of common and special types, and their myriad applications. For readers who are not quite familiar with polymers and their characteristics, it would be advisable to read Plastics Fundamentals, Properties, and Testing, before taking up the present book. We thank Allison Shatkin, Materials Science and Chemical Engineering Editor at CRC Press/Taylor Francis, who first conceived the idea of this book and took the initiative in publishing it. 

Copolymers in which the acrylate monomer is the major component are useful as ethylene-acrylate elastomers (trade name Vamac). These are terpolymers containing a small amount of an alkenoic acid to introduce sites (C=C) for subsequent cross-Unking via reaction with primary diamines [see Equation 1.34 in Chapter 1 of Plastics Fundamentals, Properties, and Testing]. These elastomers have excellent oil resistance and stability over a wide temperature range (— 50°C to 200°C), being superior to chloroprene and nitrile rubbers. Although not superior to silicone and fluoroelastomers, they are less costly uses include automotive (hydraulic systems seals, hoses) and wire and cable insulation. 

There have been substantial efforts to improve the flame resistance of nylons. Various halogen compounds (synergized by zinc oxide or zinc borate) and phosphorus compounds have been used (see the section on Flame Retardation in Chapter 1 of Plastics Fundamentals, Properties, and Testing). They are, however, dark in color. 

Degradation of polyacetals may also occur by oxidative attack at random along the chain leading to chain scission and subsequent depolymerization (unzipping). Oxidative chain scission is reduced by the use of antioxidants (see Chapter 1 of Plastics Fundamentals, Properties, and Testing), hindered phenols being preferred. For example, 2,2 -methylene-bis(4-methyl-6-r-butylphenol) is used in Celcon (Celanese) and 4,4 -butylidene bis(3-methyl-6-f-butylphenol) in Delrin (Du Pont). 

Polybenzimidazole (PBl) is the most well-known commercial example of aromatic heterocycles used as high-temperature polymers. The synthesis of PBI is carried out as follows (see also Figure 1.36 of Plastics Fundamentals, Properties, and Testing). The tetraaminobiphenyl required for the synthesis of PBl is obtained from 3,3 -dichloro-4,4 -diaminodiphenyl (a dye intermediate) and ammonia. Many other tetraamines and dicarboxylic acids have been condensed to PBl polymeric systems. 

Attempts to predict miscibility using simple solubility parameters of the type described in Chapter 1 of Plastics Fundamentals, Properties, and Testing have been largely unsuccessful because strong dipolar interactions are not taken into account. The importance of these interactions has been demonstrated, for example, with miscible mixtures of poly(acrylic esters) and poly(vinyl fluoride), where the compatibility has been attributed to dipolar interactions of the type... 

The discs themselves must be fabricated from materials that have the following characteristics (1) dimensional stability (2) optical clarity (3) isotropic expansion and (4) low birefringence (see Chapter 2 of Plastics Fundamentals, Properties, and Testing). In addition, the surface should be free of contaminating particles and occlusions that would interfere with the information retrieval process. 

Plastics fundamentals, properties, and testing / Manas Chanda and Salil K. Roy. 

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