Agent coupling

Coupling agents promote adhesion between two dissimilar phases in composite materials. They are used in small quantities to modify a surface to create a better dispersion of the material and favour agglomerate breakdown. Silane coupling agents are the most commonly used inorganic material. 

Adherence between the filler and polymer surfaces is improved using coating or wetting additives such as stearates, titanates or zirconates by improving the level of wetting of the filler by the polymer and then 

4 Reinforcing Fillers, Reinforcing Agents, and Coupling Agents 

Efficient coupling agents are silanes [1,55,62,69-71] and organotitanates [72-74], which are easily dispersed and present a high chemical resistance. Chromium coordination complexes and substances containing phosphorus are also used. 

Silane coupling agents play an important role in the production of composites made of organic polymers and inorganic fillers such as glass, minerals, metals. 

Conducting agents reduce the specific resistance. Aluminium flakes coated with coupling agents, steel microfilaments, silvered glass fibres and spheres, carbon black, carbon fibres, and organic 

Coupling agents such as neoalkoxy titanate or zirconate improve interfacial interaction and filler 

Titanium phosphates such as (12.205) are used as coupling agents to improve adhesion between polymers and fillers. Improvements in impact strength with as little as 0.1% additive have been claimed. 

In addition to preferential adsorption of epoxy components at fiber or adherend surfaces, chemically different species can be added to the interphase to improve or alter an interfacial property. Among the species, that can be added to the composite, coupling agents have a great effect on the interphase structure and properties. 

Because of the chemical and structural differences of this coupling agent interphase layer, the mechanical properties of this region would be expected to be quite different from the bulk epoxy. Indeed, Lipatov 62) has shown that the addition of silanes changes the mechanical strength and chemical resistance of interphase regions. 

Nanofillers have struggled to reach significant sales levels because of high costs, small-scale production and modest demand levels, but the situation is expected to improve dramatically with the advent of large scale manufacture. General Motors is believed to be the biggest consumer of nanoclay thermoplastic olefin eompounds at present, and was expected to use about 300 tonnes in 2004. With improvements in the scale of production and consequently 

Most of the world s flame retardants are sold directly to polymer manufacturers, masterbatch producers, compounders and fabricators. Not all the statistics for flame retardant sales confine themselves to plastics markets. Freedonia reports that 80% of US usage of FRs is for plastics. Smaller quantities are used in textiles, coatings, adhesives and elastomers. 

The geographical pattern of sales of flame retardants was forecast in a 2003 report to remain littie changed between 2001 and 2005, with Asia-Pacific taking nearly 35% of sales and Europe and North America about 30% each, while the rest of the world, including South America, Africa, Russia and the Middle East, can expect only just over a 5% share. 

In 2001, the FR market in the USA, Western Europe and Asia together was valued by SRI Consulting at nearly US 2 billion, with a sales volume of 1.2 M tonnes, i.e., an average price of 1.7/kg. Consmnption peaked in 1999-2000 and fell severely in 2001 and 2002 with serious slowdowns in the electronics, construction and transport sectors. In late 2003 and 2004 there was a slow recovery, driven mostly by new fire regulations, higher flame retardancy expectations in automotive interiors and a hesitant upturn in the global economy. 

Great Lakes has estimated the total flame retarded polymer sold in 2003 at 1.67 M tonnes worldwide. Three-quarters of this was destined for electrical and electronic products, including cable, while 24% was sold to the building and construction industry (i.e., 400,000 tonnes) and 1% went into transport applications. The amoimt of flame retardant polymer compound used in internal electrical components was estimated at 450,000 t/y, and 31% of this was thought to use polyamide. Altogether 14,000 tonnes of FR additive were used in polyamides, and 15,000 tonnes were incorporated into thermoplastic (saturated) polyesters. The majority of FRs used in PET and PBT polyesters are either brominated carbonate oligomers or brominated epoxy oligomers, while the majority of FRs used in polyamides are either brominated or polybrominated polystyrenes. 

A filler cannot be used to best advantage in a polymer unless there is good adhesion between them. In particular the filler particle-polymer interface will not be stress-bearing and therefore provides a point of mechanical weakness. 

One way of improving the adhesion between polymer and filler is to improve the level of wetting of the filler by the polymer. One approach, which has been used for many years, is to coat the filler with an additive that may be considered to have two active parts. One part is compatible with the filler, the other with the polymer. Probably the best known example is the coating of calcium carbonate with stearic acid. Such coated or activated whitings have been used particularly with hydrocarbon rubbers. It is generally believed that the polar end attaches itself to the filler particle whilst the aliphatic hydrocarbon end is compatible with the rubbery matrix. In a similar maimer clays have been treated with amines. 

It is perhaps worthwhile observing at this point that it is quite feasible to couple a chemical onto the surface of a material such as glass to reduce wetting and hence the level of adhesion by a polymer by incorporating some group incompatible with or even repellent to the polymer. 

4-Epoxycyclohexyl)-ethyl]trimethoxysilane CH, CH. Si (OCH,), Polyester Epoxide Polycarbonate 

Surface treatments with bi-functional additives, which form very strong covalent bonds to the filler and then bond to a polymer by a variety of mechanisms, are widely available. They are based on organo-metallic compounds with the general formula  

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Coupled chromophores Coupler Couplers Coupling Coupling agents... 

Tetrahydrofurfuryl alcohol is a solvent and coupling agent for a phosphate-type insecticide used to control the gypsy moth. Esters of tetrahydrofurfuryl alcohol are used in preparations employed as insect repeUents. Tetrahydrofurfuryl alcohol is also used as a solvent—carrier for an EPA-approved paper sHmicide formulation. In this appHcation, the exceptional solvent action of tetrahydrofurfuryl alcohol prevents separation of the... 

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