Reinforcing fillers aggregates

Discussion - The morphological properties of active fillers are important aspects of rubber reinforcement. The structure of the reinforcing filler is characterized by aggregates of primary particles, which form cavities for attachment and penetration of polymer molecules. The SEM pictures show that the three-dimensional morphology is basically maintained. 

Medalia, A. 1. Filler aggregates and their effect on reinforcement . In Le renforcement des elastomeres. Paris CNRS 1975, pp. 63-79... 

The isotactic polypropylene (iPP) was supplied by FiberVisions, Georgia, in the form of homopolymer pellets with a melt flow index of 35g/10 min (230 °C, 160 g) and a density of 0.91 g cm-3. The reinforcing filler was rice straw fibril and fibril aggregates (RSF) obtained from rice straw pulp fiber (Taonan paper and pulp company, Jihn ptrovinoe. North-east of China) that was cut to pass a screen (room temperature and relative humidity of 30%) with holes of 1 mm in diameter by a Willey mill before treatment. The maleated polypropylene (MAPP) was used as compatibilizing agent and Epolene G-3003 P has an acid number of 6 and a molecular mass of 125 722. 

Up to this point only the surface chemistry and size of the primary filler particles have been examined. However, important evidence exists that these particles are not randomly distributed throughout the elastomeric matrix. Indeed, much evidence shows that a complex state of aggregation is important for reinforcement in both carbon black and silica fillers. Two levels of structure have been identified in reinforcing fillers beyond the... 

It should be emphasized that high reinforcement results because of, not in spite of, the aggregation of the filler particles. In Section 10.3 a model was developed that emphasized that the filler particles must be the same size as or smaller than the chain end-to-end distance for maximum reinforcement. This model can be extended to filler aggregates surrounded by polymer network chains. The close interlocking of filler aggregate and polymer network, both structures having similar dimensions, allows for maximum reinforcement. 

Let us consider the case III. In the case of percolation, that is, if transition layers in a polymer matrix, around embedded active filler aggregates, connect (or touch) each other, the effect is significantly increased, extending itself through the whole macrosystem and resulting in reinforcement effects. So, polymer chains not filler particles, are the main actors of reinforcement. The connections between layers are strain-dependent, so different kinds of reinforcement effects arise. 

Let us now get back at our model and apply it to conditions corresponding to Payne s experiments. Under low deformations, only the outer part of the gradient reinforcing layer around the filler aggregates... 

Apart from the three factors discussed above, another factor which affects reinforcement is the degree of filler dispersion. It is necessary that during mixing of filler with the rubber, the filler aggregates are broken down to... 

Table 10.15 Approximate ranges of experimental techniques to study blend morphology of (1) interatomic (2) molecular, spherulites (3) Filler aggregates, compatibilized blends (4) reinforcements, immiscible blends (5) Voids (Utracki 1989) ...

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