General advantages depend on the type of compound. PVC is regarded as perhaps the most versatile thermoplastic resin, due to its ability to accept an extremely wide variety of additives such as plasticizers, stabilizers, fillers, processing aids, impact modifiers, lubricants, foaming agents, biocides, pigments, reinforcements, and so forth. Michel Biron, in A Practical Guide to Plastics Sustainability, 2020 10.19.1 General Advantages They are chemically identical to the accelerators for UP resins. Agents that speed up the oxidative drying process of natural drying oils in coating technology (Chapter 10.03) are called dryers or siccatives. For ambient temperature, cure reducing agents such as tertiary aromatic amines or heavy metal salts of Co, Va, or Fe are often employed as accelerators. Polyester resins and UP resins are usually cured by addition of peroxides, which generate free radicals and cause cross-linking. However, a variety of other curing agents containing active hydrogen atom, such as melamine-formaldehyde, urea-formaldehyde, polysulfides, or mercaptans, 25 have been used. The main chemistries on which ECAs are based are polyamides and aliphatic amines (Chapter 10.28). The choice of the epoxy curing agent (ECA) depends on the processing method, curing conditions, physical and chemical properties desired, and toxicological and environmental limitations. Curing agents react with molecules and are coupled directly into the cured system as a structural moiety of the polymer.Įpoxy resins by curing form a three-dimensional and infusible network. An agent that does not enter into the reaction is called a catalyst. Substances that promote or control the cross-linking reaction are called curing agents. Curing initiates a change in the molecular structure or even creates a new polymer (curing of a polyol with a polyisocyanate yielding a polyurethane (PUR)). The cure (or ‘cross-linking’) may be done through heat (generally above 200 ☌), through irradiation, or through a chemical reaction. Whereas thermoplastic resins usually are fully polymerized when submitted to processing, thermosetting resins are prepared for processing in an uncured state, and they are irreversibly cured during the processing stage. Höfer, in Polymer Science: A Comprehensive Reference, 2012 10.21.4.6 Curing Agents
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