Heat resistance, improvement

Heat resistance is iafluenced by both the type and extent of cure. The greater the strength of the chemical bonds ia the cross-link, the better is the compound s heat resistance. Peroxide cure systems, which result ia carbon—carbon bonds, result ia a range of sulfur cross-links varyiag from 1 to > 30 sulfur atoms per cross-link, and heat resistance improves as the number of more thermally stable short cross-links predominates. This is an important factor ia designing the desired cure system. 

Kraton Polymers has developed a multiarm SIS (Kraton 1320X [37,46,47,50]) and SBS (Kraton KX-222C, [48,49]) for rapid UV/e-beam cure. Besides heat resistance improvements, plasticizer resistance is also improved in cured rubber-based systems. The dioctyl phthlate plasticizer common in PVC backing films is soluble in the styrenic domains of SBCs. Crosslinking of the mid-block provides cohesion even after plasticizer attack [51]. 

Cured polyimide resins, (IV), used as coatings for semiconductor devices were prepared by Akiba [4] that had good heat resistance, improved adhesion to substrates, and resistance to thermal deterioration. 

Aminoplasts based on urea-benzoguanamine-formaldehyde oligomers when compared to urea-formaldehyde press-materials are distinguished by an increased water- and heat-resistance, improved physico-mechanical properties, and insignificant shrinkage. 

Chromium Cr 0.6-1.2, C 0.2-0.5 Improved strength, toughness, heat resistance Improved castings, stainless steels... 

Features Exc. antiblocking props, when added to flexographic and gravure inks, water and solv.-based wood finishes exc. heat resist. improved sol. resist, and recoatability than micronized syn. waxes Properties Finely micronized powd. 

Uses Latex for dipped goods requiring high modulus, abrasion and heat resistance, improved tear strength, ozone and weathering resistance... 

Improved dimensional stability Improved heat resistance Improved processability Improved toughness Improved weatherability Improved solvent resistance Improved flame resistance Improved moisture resistance Improved esthetics and appearance, etc. 

Resins (eg coumarone-indene resins) Improved building tack Improved heat resistance Improved tear strength High vulcanizate hardness Improved abrasion resistance Improved crystallization resistance... 

Pre-accelerated, low viscosity fast wet-out, thixotropic, low styrene emission, orthophthalic resin, offering good interlaminar adhesion, high heat resistance, improved water resistance and low exotherm enabling thick sections to be fabricated by either hand-lay or spray/projec ion techniques colour change on cure. Approved for food contact applications, Lloyd s and Det Norske Veritas. 

Thermoplastic rubbers Good environmental and heat resistance improved aging characteristics versus PE... 

Rubbers used in hoses and belting are reviewed and several examples of cure systems and antidegradant packages for use in hose and belting compositions, which can increase heat resistance, improve flex fatigue and provide ozone resistance are presented and discussed. 22 refs. (2001 meeting of the All India Rubber Industries Assn.)... 

Nylon 6 and 6/6 possess the maximum stiffness, strength, and heat resistance of all the types of nylon. Type 6/6 has a higher melt temperature, whereas type 6 has a higher impact resistance and better processibility. At a sacrifice in stiffness and heat resistance, the higher analogs of nylon are useful primarily for improved chemical resistance in certain environments (acids, bases, and zinc chloride solutions) and for lower moisture absorption. 

Dimensional Stability. The wet heat resistance of PVA fiber is indicated by the wet softening temperature (WTS) at which the fiber shrinks to a specified ratio. At one time, the WTS was not more than 95°C for nonacetalized PVA fiber, but improvement of WTS has been achieved by improvement in heat-drawing and -treating techniques other methods proposed include suppression of polymerization temperature of vinyl acetate (36) and employment of alkafi spinning (37). 

In other areas, POD has been used to improve the wear resistance of a mbber latex binder by incorporation of 25% of Oksalon fibers. Heat-resistant laminate films, made by coating a polyester film with POD, have been used as electrical insulators and show good resistance to abrasion and are capable of 126% elongation. In some instances, thin sheets of PODs have been used as mold release agents. For this appHcation a resin is placed between the two sheets of POD, which is then pressed in a mold, and the sheets simply peel off from the object and mold after the resin has cured. POD-based membranes exhibit salt rejection properties and hence find potential as reverse osmosis membranes in the purification of seawater. PODs have also been used in the manufacturing of electrophotographic plates as binders between the toner and plate. These improved binders produce sharper images than were possible before. 

A Methylolhydantoins. l,3-Bis(hydroxymethyl)-5,5-dimethyIhydantoia [6440-58-0] is used extensively as a preservative in cosmetic and industrial appHcations, and carries EPA registration for the industrial segment. It is available in soHd and in aqueous solution forms, including low free formaldehyde versions of the latter. A related derivative, l,3-bis(hydroxyethyl)-5,5-dimethyIhydantoia [26850-24-8] is used in the manufacture of high temperature polyesters, polyurethanes, and coatings, offering improved heat resistance, uv stabiUty, flexibiUty, and adhesion. 

Improved heat resistance is the most important advantage of cross-linked polyethylene (XITK) over thermoplastic polyethylene. A power cable... 

Because the heat distortion temperature of cured epoxy resins (qv) increases with the functionality of the curing agents, pyromellitic dianhydride is used to cross-link epoxy resins for elevated temperature service. The dianhydride may be added as a dispersion of micropulverized powder in liquid epoxy resin or as a glycol adduct (158). Such epoxies may be used as an insulating layer in printed circuit boards to improve heat resistance (159). Other uses include inhibition of corrosion (160,161), hot melt traffic paints (162), azo pigments (163), adhesives (164), and photoresist compounds (165). 

Silicone resins with high phenyl contents may be used with medium or short oil alkyds as blends in air-dried or baked coatings to improve heat or weather resistance the alkyd component contributes to adhesion and flexibiUty. AppHcations include insulation varnishes, heat-resistant paints, and marine coatings. 

Small amounts of TAIC together with DAP have been used to cure unsaturated polyesters in glass-reinforced thermo sets (131). It has been used with polyfunctional methacrylate esters in anaerobic adhesives (132). TAIC and vinyl acetate are copolymerized in aqueous suspension, and vinyl alcohol copolymer gels are made from the products (133). Electron cure of poly(ethylene terephthalate) moldings containing TAIC improves heat resistance and transparency (134). 

Thiuram Sulfides. These compounds, (8) and (9), are an important class of accelerator. Thiurams are produced by the oxidation of sodium dithiocarbamates. The di- and polysulfides can donate one or more atoms of sulfur from their molecular stmcture for vulcanization. The use of these compounds at relatively high levels with litde or no elemental sulfur provides articles with improved heat resistance. The short-chain (methyl and ethyl) thiurams and dithiocarbamates ate priced 2/kg. Producers have introduced ultra-accelerators based on longer-chain and branched-chain amines that are less volatile and less toxic. This development is also motivated by a desire to rninirnize airborne nitrosamines. 

Vluorosilicone. By fluorinating the siHcone polymer molecule it is possible to improve the solvent, fuel, and oil resistance of this already heat-resistant class of elastomers. The resulting polymers are especially useful in select automotive seals and gaskets as weU as military and downhole oilfield parts. 

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