Curing composites and

There are at least two problems in impregnating wet materials. First, water is a mechanical obstacle for permeation of the organic composition into the volume of the materied. Second, water impedes the wetting of the surface of the pores of the material by the composition. If a water film exists between the cured composition and the solid, the strengthening effect of the impregnation will be minimal. 

The bonded area should be large enough to resist the greatest force that the joint will be subjected to in service. The calculation of stress in the adhesive joint is not a reliable way of determining the exact dimensions required. It is relatively difficult to decide on an allowable stress. The strength of the bond is affected by environmental conditions, age, temperature of cure, composition and size of adherends, and the thickness of the adhesive layer. 

Mitsubishi Chemical manufactures a seismic retrofit material Replark and have formed a joint venture with Fiberite in the USA. Replark is a UD carbon fiber tape with low epoxy resin content with a fiberglass scrim backing to facilitate handling in the field. The application entails the preparation of the concrete, application of an epoxy primer, putty and resin, followed by the requisite number of layers of Replark tape and additional resin, to form a cured composite and finally, the application of a surface coat to improve the appearance. Fiberite use type 12k T300 or AS4C carbon fiber and the Replark is offered in areal weights from 175 300 gm . ... 

Network characterisation (cross-linked systems, rubbers, curing, compositional and degradation studies)... 

The literature is abundant in data on the photochemical behavior of thermosetting matrices based composites. Most of the reported data focused on two main issues (a) the UV-cured composites and nanocomposites and (b) the photochemical degradation of these materials upon UV exposure. In the first case, the UV radiation is employed in the synthesis of various materials starting from thermoset precursors included in complex formulations that may also contain— besides fillers, whether fibers or particles— initiators, plasticizers, compatibilizing agents, UV absorbers. 

The routine compositional and functional testing done on the adhesives includes gas chromatographic testing for purity, potentiometric titrations for acid stabilizer concentrations, accelerated thermal stabiUty tests for shelf life, fixture time cure speed tests, and assorted ASTM tests for tensile shear strengths, peel and impact strengths, and hot strengths. 

Polyimides (PI) were among the eadiest candidates in the field of thermally stable polymers. In addition to high temperature property retention, these materials also exhibit chemical resistance and relative ease of synthesis and use. This has led to numerous innovations in the chemistry of synthesis and cure mechanisms, stmcture variations, and ultimately products and appHcations. Polyimides (qv) are available as films, fibers, enamels or varnishes, adhesives, matrix resins for composites, and mol ding powders. They are used in numerous commercial and military aircraft as stmctural composites, eg, over a ton of polyimide film is presently used on the NASA shuttle orbiter. Work continues on these materials, including the more recent electronic apphcations. 

Microwaves have also been studied for a variety of curing, bonding, and drying apphcations for plastics and composite materials (qv) (181). 

Unsaturated polyester resins predominate among fiber-reinforced composite matrices for several reasons. A wide variety of polyesters is available and the composites fabricator must choose the best for a particular appHcation. The choice involves evaluation of fabrication techniques, temperatures at which the resin is to be handled, cure time and temperature desked, and requked cured properties (see Polyesters, unsaturated). 

The role played by the various ingredients in the composition of sealant, and in particular on the durability of adhesion has been discussed recently [77]. Inert plasticizers, such as trimethylsilyl-endblocked-PDMS, are typically added to silicone sealant compositions in order to adjust the rheology of the uncured sealant. They result in a reduction of the modulus and hardness of the cured sealant. Differences in the durability of silicone sealants are found to be due to differences in their cure chemistry, and more specifically to the nature and... 

Even the earliest reports discuss the use of components such as polymer syrups bearing carboxylic acid functionality as a minor component to improve adhesion [21]. Later, methacrylic acid was specifically added to adhesive compositions to increase the rate of cure [22]. Maleic acid (or dibasic acids capable of cyclic tautomerism) have also been reported to increase both cure rate and bond strength [23]. Maleic acid has also been reported to improve adhesion to polymeric substrates such as Nylon and epoxies [24]. Adducts of 2-hydroxyethyl methacrylate and various anhydrides (such as phthalic) have also been reported as acid-bearing monomers [25]. Organic acids have a specific role in the cure of some blocked organoboranes, as will be discussed later. 

Typical features of a plywood resole formulation are a formaldehyde-to-phenol molar ratio in the 2.0 1 to 2.5 1 range, programmed formaldehyde, an alkali content from 4 to 8 wt% (calculated as sodium hydroxide), and pan solids of 40-50%. Resins used for laminated veneer lumber (LVL) tend to be similar to plywood resins in composition and molecular weight, though they are often designed for high-end cure speed. 

The term cocuring means that two parts that must be fastened together are cured simultaneously and in contact to achieve permanent bonding between them. The process applies equally to thermoset-matrix composite materials and to thermoplastic-matrix composite materials (except the cocuring of two thermoplastic-matrix parts is not, of course, permanent). 

Table 13 Blend Composition and Dynamic Curing Characteristics for NR-LDPE ...

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