Thermoplastics and Thermosets

From the point of view of technology, it is convenient to classify polymers as thermosetting and thermoplastic. The former set by chemical crosslinks introduced during fabrication and hence do not change appreciably in their deformability with changes in temperature. Thermoplastics, on the other hand, soften and/or melt on heating and can therefore be altered in shape by heating... 

Polymers are characteri2ed as thermosetting and thermoplastic with respect to the methods by which they are joined. Thermosetting polymers are permanently hard and do not soften upon the apphcation of heat they are joined by mechanical fasteners and adhesives. Several methods have been devised to join thermoplastic polymers, as weU as thermoplastic composite materials, which soften upon heating. 

The two primary types of plastics, thermosets and thermoplastics, are made almost exclusively from hydrocarbon feedstocks. Thermosetting materials are those that harden during processing (usually during heating, as the name implies) such that in their final state they are substantially infusible and insoluble. Thermoplastics may be softened repeatedly by heat, and hardened again by cooling. 

Production and Sales and Captive Use of Thermosetting and Thermoplastic Resins, Society of the Plastics Industry, Committee on Resiu Statistics, Ernst and... 

Asbestos fibers have likewise been used in reinforcement of plastics such as poly(vinyl chloride), phenoHcs, polypropylene, nylon, etc. Reinforcement of both thermoset and thermoplastic resins by asbestos fibers has been practiced to develop products for the automotive, electronic, and printing industries. 

Fig. 5. Interlaminar fracture toughness, for a number of thermosetting and thermoplastic composites (36,37). Open white bars represent glass-fiber composites shaded bars are for carbon fibers. The materials are A, polyester (unidirectional) B, vinyl ester (CSM = chopped strand mat) C, epoxy (R/BR1424) D, epoxy (T300/914) E, PPS F, PES and G, PEEK. To convert J/m to fdbf/in. multiply by 2100.

Table 1. Mechanical Properties and Relative Costs of Thermosetting and Thermoplastic Composites...

Thermosetting and Thermoplastic Resins, year-end monthly or annual statistical reports, the Committee on Resin Statistics of the Society of the Plastics Industry, Inc., Washington, D.C., through 1991. 

Today the phenol-formaldehyde moulding compositions do not have the eminent position they held until about 1950. In some, important applications they have been replaced by other materials, thermosetting and thermoplastic, whilst they have in the past two decades found use in few new outlets. However, the general increase in standards of living for much of this period has increased the sales of many products which use phenolics and consequently the overall use of phenol-formaldehyde moulding powders has been well maintained. 

Various thermosetting and thermoplastic resins BS 3900 Powder/liquid system in factory. Airless spray/trowel in field Superior chemicai and abrasion resistance compared with enamels. Comparatively expensive. Simultaneous coating internally/externally possible. Various resins available to suit particular requirements. 

The difference between thermosets and thermoplastics is more obvious when processing is considered ... 

Thermosets and thermoplastics behave differently from each other in fires. Thermosets do not melt when heated but may well undergo further crosslinking. The presence of such additional crosslinks hinders movement of any volatile degradation products through the polymer matrix. Hence the combustion zone tends to be starved of fuel and for this reason thermosets tend to be relatively non-flammable. 

Both thermosets and thermoplastics are used as food-contact materials, though thermoplastics predominate in this appfication. Examples of the former are phenol- and urea-formaldehyde, while probably the best known example of the latter is low-density poly(ethylene). Other linear polymers are used include high-density poly(ethylene), poly(propylene), and PVC, all of which find quite extensive use. Polymers for food packaging may be in the form of films and other flexible items, or in the form of rigid containers, such as clear drinks bottles or opaque cartons for dairy products. 

Recycling of glass fibre-reinforced plastics is reviewed, with special emphasis on remelting of thermoplastic composites, mechanical recycling of thermoset composites, depolymerisation and dissolution of thermosets and thermoplastics, closed loop recycling of glass, and the use of glass as a mechanical compatibiliser. 32 refs. 

Tab. 5.26 Optimum conditions for ultrasonic compression moulding of thermosets and thermoplastics.

You 11 recall that thermosets are polymAs that have lots of cross-linking. The molecules are three-dimensional, rather than two. More importantly, once the cross-linking bonds are in place, the polymer becomes rigid and hard. Put another way, once the thermoset occurs, it is irreversibly set. That s the difference between thermosets and thermoplastics. The latter can be remolded and reshaped the former cannot. When you sweep up the scrap material around the molding/extruding machines that handle thermosets, you throw it away. 

Foamed polymers. Thermosets and thermoplastics formed into low density, cellular materials containing bubbles of gas. Rigid foams have their gas bubbles in closed cells, inhibiting flexibility flexible foams have the bubbles in open cells, permitting the gas to escape as the foam is flexed. 

Vautey, P. and Favre, J.P. (1990). Fiber/matrix load transfer in thermoset and thermoplastic composites-single fiber models and hole sensitivity of laminates. Composites Sci. Technol. 38, 271-288. 

Srinivasan. K., Jackson, W.C., Smith, B.T.. Hinkley, J.A. (1992). Characterization of damage in impact thermoset and thermoplastic composites. J. Reinforced Plast. Compo.sites II, 1111-1126. 

Frequency dependent complex impedance measurements made over many decades of frequency provide a sensitive and convenient means for monitoring the cure process in thermosets and thermoplastics [1-4]. They are of particular importance for quality control monitoring of cure in complex resin systems because the measurement of dielectric relaxation is one of only a few instrumental techniques available for studying molecular properties in both the liquid and solid states. Furthermore, It is one of the few experimental techniques available for studying the poljfmerization process of going from a monomeric liquid of varying viscosity to a crosslinked. Insoluble, high temperature solid. 

The Argon theory, therefore, consistently interprets the yield behavior of both thermosets and thermoplastics. This indicates that crosslinks in thermosets do not introduce appreciable deviation to the kink formation process described. This point is also supported by Ygmani and Young s finding of the molecular parameters, z and a, being insensitive to crosslinking density for DGEBA cured with different amount of TETA. 

Both thermoset and thermoplastic resin systems are employed in the construction of composites (Table 8.3). The most common thermoset resins are polyimides, unsaturated polyesters, epoxys, PFs, and amino-formaldehydes. A wide variety of thermoplastic resins have been developed. 

Polymers are often divided according to whether they can be melted and reshaped through application of heat and pressure. These materials are called thermoplastics. The second general classification comprises compounds that decompose before they can be melted or reshaped. These polymers are called thermosets. While both thermoset and thermoplastic polymers can be recycled, thermoplastic recycling is easier and more widespread because thermoplastic materials can be reshaped simply by application of heat and pressure. 

A very wide range of plastics are coloured with pigments including PVC, polystyrene, polyurethane, polyamide, polycarbonate, polyester, elastomers, thermosets and thermoplastics. The choice of pigment is obviously dependent on which plastic... 

Table 7.1 Comparison of Thermosetting and Thermoplastic Matrix Composites...

There are a number of general references available that contain detailed descriptions of the winding process and equipment itself [5,6], The purpose of this work, however, is to focus on the relationship between processing conditions and final part quality for both thermosetting and thermoplastic matrix filament wound cylinders. In the subsequent sections, an overview of the process will be presented, followed by detailed descriptions of current process modeling techniques and methods for determining cylinder quality. 

Process models allow composite case manufacturers to determine the affects of process variable settings on final cylinder quality. Because the cost of a composite cylinder can be as great as 500,000, the ability to simulate filament winding can significantly reduce cost and improve quality. Several computer models of the filament-winding process for both thermoset and thermoplastic matrix materials have been developed. These models are based on engineering principles such as conservation of mass and energy. As such, numerous resin systems and fiber materials can be modeled. 

Flow charts with relevant inputs and outputs for each submodel are shown in Figures 13.7 and 13.8 for winding of thermosetting and thermoplastic composite cylinders, respectively. The primary differences between process models for thermosetting and thermoplastic cylinders arise in (1) the method of heating, and (2) the mechanics of consolidation/ fiber motion. 

In the following sections, the basic modeling approaches for thermosetting and thermoplastic matrix composite cylinders will be summarized. Differences between the thermosetting and thermoplastic model approaches are highlighted. 

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