Polychloroprene rubber fillers

Lee [242] studied the dependence of the physico-mechanical properties of Wollastonite-filled polychloroprene rubber on the type of agent used to pre-treat the filler. The composition contained 26.9 part (weight) of the filler per 100 parts (weight) of the rubber (compositions CR-1100, CR-174, CR-151). The finishing agents were y-aminopropyl triethoxysilane (CR-1100 and CR-174) and vinyl triethoxysilane (CR-151). The mechanical properties of the compositions are listed in Table 7 below. The author proposed an empirical equation to relate the modulus with the equilibrium work of adhesion in the following form ... 

Solvents produce different effects than do corrosive chemicals. Both silica and carbon black filled natural rubbers were more resistant to solvents than unfilled rubber. Also, the cure time was important, indicating that the bound rubber plays a role in the reduction of a solvent sorption. The diffusion coefficient of solvents into rubbers decreases with longer cure times and higher fillers loadings. Polychloroprene rubber swollen with solvent has a lower compression set when it is filled with carbon black. 

Rubber compositions (especially polychloroprene rubber) with boron nitride fillers serve as sealing materials, adhesives, gas-permeation-resistant materials for accumulator casing, and for pressure-sensitive conductive rubber composites [91 to 96]. 

This compound also uses Neoprene W type polychloroprene rubber. The compound, though coloured black with a few parts of carbon black is mainly filled with silica, which is a reinforcing mineral filler. The silica also helps to bond the rubber to the steel cords other ingredients added for this purpose include cobalt naphthenate. A commonly used system for this purpose is one comprising resorcinol and hexamethylene tetramine (HMT) which acts as a formaldehyde donor to form a phenolic resin in situ, but this is not suitable for Neoprene compounds because resorcinol is a fast accelerator for Neoprene vulcanization and interferes with its processing safety. 

Fumed silicas (Si02). Fumed silicas are common fillers in polychloroprene [40], natural rubber and styrene-butadiene rubber base adhesives. Fumed silicas are widely used as filler in several polymeric systems to which it confers thixotropy, sag resistance, particle suspension, reinforcement, gloss reduction and flow enhancement. Fumed silica is obtained by gas reaction between metallic silicon and dry HCl to rend silica tetrachloride (SiCU). SiC is mixed with hydrogen and air in a burner (1800°C) where fumed silica is formed ... 

Haslam et al. [32] reported the determination of Al in polyolefins by AAS. Typical AAS tests on rubber compounds involve several steps. The sample is combusted, and the resulting ash is dissolved in distilled de-ionised water. The solution is then used for AAS [126]. AAS or EDS can also be used for element analysis of filler particles. In order to determine the uniformity of tin compounds in polychloroprene after milling and pressing, Hornsby et al. [127] have ashed various pieces from one composition. After fusion of the residue with sodium peroxide and dissolution in HC1, the Sn content was determined by means of AAS. Typical industrial AAS measurements concern the determination of Ca in Ca stearate, Zn in Zn stearate, Ca- and Zn stearate in PE, Ca and Ti in PE film or Al and V in rubbers. 

An activator in rubber compounds containing organic accelerators. In polychloroprene, zinc oxide is considered to be the accelerator rather than the activator. The use of zinc oxide as a reinforcing agent and as a white colouring agent is obsolescent. Zinc oxide is manufactured by either the French (or indirect) process or by the American (or direct) process. It can be used as a filler to impart high thermal conductivity. 

Flexible Ebonite This can be called semi-ebonite usually loaded with mineral fillers with a lower proportion of sulphur, say 15 phr, and by incorporating into the compound synthetic rubbers like polychloroprene, polyisobutylene or butyl rubber. This ebonite will have good resistance to impact. A sheet made of flexible ebonite will look like a hard flexible leather. 

Elastomers include natural rubber (polyisoprene), synthetic polyisoprene, styrene-butadiene rubbers, butyl rubber (isobutylene-isoprene), polybutadiene, ethylene-propylene-diene (EPDM), neoprene (polychloroprene), acrylonitrile-butadiene rubbers, polysulfide rubbers, polyurethane rubbers, crosslinked polyethylene rubber and polynorbomene rubbers. Typically in elastomer mixing the elastomer is mixed with other additives such as carbon black, fillers, oils/plasticizers and accelerators/antioxidants. 

Non- or semi-reinforcing fillers These are usually added to reduce cost. In natural rubber or polychloroprene, they may be used alone, but with non-crystallizing polymers such as butadiene - acrylonitrile or styrene - butadiene copolymers, they can only be used in conjunction with a reinforcing filler. Their effect is to reduce tensile strength and elongation, tear resistance and resistance to set. The effect on modulus varies according to choice of filler, but it is always much weaker than that of a reinforcing filler. 

The part may need to be in contact with service fluids such as mineral and vegetable based oils. The selection of the correct polymer depends on the exact nature of the fluid and the service temperature. For mineral oils a polychloroprene or acrylonitrile -butadiene copolymer based compound may be appropriate but small variations in lubricant constituents make it worthwhile to measure the changes that can occur at operating temperatures to properties such as modulus and tear resistance. For solvents it may be more viable to use a physical sheath of an impervious material such as polytetrafluoroethylene. Swelling or shrinkage is strongly influenced by the nature of fillers and oils used to compound the rubber. 

More important and with better properties are the cold-setting, two-component acrylate adhesives, which contain methacrylates or acrylates, sometimes mixed with styrene and methacrylic acid as monomer and, in addition, various polymers. The polymers used are primarily synthetic rubbers, such as polychloroprene, styrene-butadiene rubber, butyl rubber, polystyrene, polymethacrylates, and acrylate graft polymers of these polymers. Amines are used as accelerators, and benzoyl peroxide in the form of plasticizer pastes or a powder mixture with fillers is preferred as hardener [43]. 

Another study that concerned the use of an activated rubber crumb was also performed by Adov and co-workers [43]. They introduced a finely ground activated polychloroprene powder into a virgin chloroprene compound and made a quantitative assessment of the Payne effect in the vulcanisate. They produced data that showed the dependence of the real and imaginary parts of the dynamic shear modulus, and the dependence of the mechanical loss tangent on the logarithm of the strain amplitude for vulcanisates containing different contents of activated powder. Their results indicated that the introduction of the activated chloroprene powder into the vulcanisate promoted an improvement in the interaction of the rubber with the filler present in the compound, which should lead to an increase in the level of service properties for the products and open up a route for the effective re-use of the rubber waste. 

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