Abrasion resistance, particle strength

Composite Particles, Inc. developed two methods of surface modification of polymeric materials which are used for materials of different shapes and compositions. Here, only the spherical, non-rubber particles are discussed. Further information is included in the section on rubber particles below. One method of surface modification is based on exposing the polymeric powder to a chemically reactive gas atmosphere which oxidizes surface groups to form OH and COOH functionalities. These functionalities are then available for reaction with the components of the matrix into which modified particles are introduced. Vistamer HD and UH are manufactured by this method from polyethylenes of different molecular weights. Two factors can be regulated here the properties of the core particle and the type and density of functional groups on the surface of these particles. Polyethylene is a material, which without this modification, will not be compatible with most systems. The surface modification allows the incorporation of the material into resins. This improves abrasion resistance, tear strength, and moisture barrier properties and reduces the fiiction coefficient. 

Elastomers are often compounded with finely divided solids to reinforce the rubber and to reduce costs. The most important fillers are carbon blacks, silica and silicates, clays and whiting (calcium carbonate). " The particles are the source of reinforcement through their interactions with the rubber, among themselves and with the chemistry of the cross-linking process. Abrasion resistance, tear strength and tensile strength are simultaneously improved. However, hysteresis, heat build-up and compression set (permanent deformation) are also known to increase as the reinforcing ability of the filler becomes more pronounced. 

Over the years poly vinyl alcohol (abbreviated PVOH or PVAl) proofed to be the most preferred protective colloid for that purpose. In a cementitious environment PVOH will be partly saponified and also absorbed of fine particles within a mortar, i.e. cement and fillers. This results in a film forming of the dispersed polymer and finally the polymer film is not redispersible any more. Since the polymer film (acting as a binder) is distributed throughout the cement matrix it improves dramatically the adhesion, abrasion resistance, flexural strength, flexibility, water impermeability/water repellency (hydrophobicity) and workability of a cementitious system. 

Therefore, the section shown in Figure 15, and the pore network in 3-D from which it arises, are both absolutely defined in a quantitative way. Inasmuch as the 3-D networks are felt to be a realistic representation of random pore spaces, it is feasible to compute directly several important macroscopic properties for the FCC powder particles. Amongst these properties are permeability and effective difflisivity, so that diffusion and reaction calculations relevant to gas-oil cracking in the FCC particles can be directly undertaken. Also important in this respect are calculations of deactivation due to coke laydown within the particles. It is also possible that the pore networks could be used to deduce strength and abrasion resistance of the particles. 

The second method of surface modification permits the formation of a composite particle, the core of which is composed of polymer (UHMWPE or polyimide) and the surface of which is coated with titanium carbide which is hard and abrasion resistant. The composite particles can be incorporated into any suitable matrix resulting in improved abrasion resistance, lowered fiiction, higher compressive strength, improved creep resistance, etc. This new product is a unique form of raw material which has the potential to improve the properties of many products. 

Product Particle size and distribution/dust Strength/abrasion resistance Bulk density/porosity Dispersibility/solubility/reactivity Processing time ... 

Rather peculiar to the rubber industry is the use of the fine particle size reinfordng fillers, particularly carbon black. Fillers may be used from 50 phr to as high as 100-120 phr or even higher proportions. Their use improves such properties as modulus, tear strength, abrasion resistance, and hardness. They are essential with amorphous rubbers such as SBR and polybutadiene that has Kttle strength without them. They are less essential with strain-crystallizing rubbers such as NR for many applications but are important in the manufacture of tires and related products. 

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