Thermosetting plastics , adhesives

Uses Filler for architectural and traffic paints/coatings, thermoset plastics, adhesives, caulks, and sealants, friction prods., rubber compds., polyester BMC... 

Usage of phosphoms-based flame retardants for 1994 in the United States has been projected to be 150 million (168). The largest volume use maybe in plasticized vinyl. Other use areas for phosphoms flame retardants are flexible urethane foams, polyester resins and other thermoset resins, adhesives, textiles, polycarbonate—ABS blends, and some other thermoplastics. Development efforts are well advanced to find appHcations for phosphoms flame retardants, especially ammonium polyphosphate combinations, in polyolefins, and red phosphoms in nylons. Interest is strong in finding phosphoms-based alternatives to those halogen-containing systems which have encountered environmental opposition, especially in Europe. 

Another use of urea is for resins, which are used in numerous applications including plastics, adhesives, moldings, laminates, plywood, particleboard, textiles, and coatings. Resins are organic liquid substances exuded from plants that harden on exposure to air. The term now includes numerous synthetically produced resins. Urea resins are thermosetting, which means they harden when heated, often with the aid of a catalyst. The polymerization of urea and formaldehyde produces urea-formaldehyde resins, which is the second most abundant use of urea. Urea is dehydrated to melamine, which, when combined with formaldehyde, produces melamine-formaldehyde resins (Figure 96.2). Melamine resins tend to be harder and more heat-resistant than urea-formaldehyde resins. Melamine received widespread attention as the primary pet food and animal feed contaminant causing numerous cat and dog deaths in early... 

In general, unfilled thermosetting plastics tend to be harder, more brittle, and not as tough as thermoplastics. Thus, it is common practice to add filler to thermosetting resins. These fillers can affect the nature of the adhesive bond (either positively or negatively) and are a possible source of lot-to-lot and supplier-to-supplier variability. 

These plastics represent at least 90wt% of all plastics consumed worldwide. Unlike thermoset plastics, they are in many cases reproccssable without any or serious losses of properties. There are those than can have limitations of heat-distortion temperatures, cold flow and creep, and are more likely to be damaged by chemical solvent attack from paints, adhesives, and cleaners. When injection molded, dimensional integrity and ultimate strength are more dependent on the proper process control molding parameters than is generally the case with TSs. 

Plastics can be placed into two main categories, thermoplastic and thermoset. Thermoset plastics are irreversibly formed into a permanent shape often by applying heat. Thermosets caimot be softened and remoulded on heating and have few applications in food packaging, except for the iimer linings used for can coatings and many adhesives, as used, for example, in multilayer materials. A limited range of food contact materials is made from thermosets, predominantly melamine resins and unsaturated polyesters used in tableware and utensils. 

Thermosetting Foam Substrates Most thermosetting plastics are not particularly difficult to bond. Obviously, solvent cementing is not suitable for bonding thermosets to themselves, since they are not soluble. In some cases solvent solutions can be used to join thermoplastics to thermosets. In general, adhesive bonding is the only practical method of joining a thermoset to itself or to a non-plastic material. Epoxies or modified epoxies are the most widely used adhesives for thermosets (1). 

With the flexibility of the blown film extrusion process, one-step production of wide multilayer films is possible. Incorporating a built-in adhesive layer, PVDF films can be laminated directly onto various thermo and thermoset plastics or primed metal substrates. PVDF films can protect the esthetics of UV sensitive substrates while also providing a thermal, chemical, and abrasion-resistant barrier. Recently, white PVDF films have been commercialized that are of full opacity in the UV range of 290 00 Most recently,... 

Solvent-based adhesives are adhesives with polymers dissolved or pasted in organic solvents. The solvents or solvent mixtures are only processing aids and have to be removed, either partly or completely, from the applied liquid adhesive layer through evaporation or penetration prior to the fixing of the adherends. The first case is necessary for solvent-impermeable materials (metals, glass, thermosetting plastics), the second case concerns porous and solvent-permeable materials (paper, cardboard, wood, leather). This process can be accelerated by heat supply. Solvents are mainly esters, ketones, if applicable, portions of different alcohols. The total solvent portion ranges between 75-85%. 

Bonding of thermoset plastic materials Due to their insolubility, thermoset plastic materials (e.g., items made of Bakelite, expoxy resin, boards with melamine urea coatings) are not bondable by surface dissolving with solvent-containing adhesives. 

Thermoset material Plastic/adhesive layer consisting of molecule structures closely crosslinked by covalent bonds. A thermoset material is neither fusible, nor plastically deformable and is insoluble in solvents. 

In cemented assemblies of thermoset plastics and metals, where structural strength is generally desired, the adhesive must be more rigid than those used for bonding plastic to plastic, i.e., one with modulus, strength, and coefficient of thermal expansion between those of the plastic and the metal. In many cases, such adhesives are stronger than the plastic itself... 

ADHESIVES TECHNOLOGY HANDBOOK by Arthur H. Landrock HANDBOOK OF THERMOSET PLASTICS edited by Sidney H. Goodman... 

Polyester resins (alkyds) were commercialized for coatings use in 1926, and unsaturated polyesters were used as thermoset fiberglass composite matrix resins in the 1940s, but the early resins made poor adhesives. When flexibilized resins appeared in the 1950s, they were used as adhesives. Today, unsaturated polyesters are widely used as adhesives for thermoset plastics bonding, and even for metal bonding in most countries, but are seldom used as adhesives in the United States, where the more expensive epoxy adhesives are used in similar applications. The saturated polyesters, used as thermoplastic hot-melt adhesives, seem to have appeared in the literature first in the 1954—1957 period. 

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