Compounding mineral fillers

The chemistry of flame-retardant additives is highly varied and is optimised not only for specific polymer chemistries, but also to address flammability effects such as flame spread, dripping, smoke release and so on. Flame-retardant chemistry includes classes of compounds such as halogenated organics, char formers, crosslinking compounds, mineral fillers, intumescent packages, phosphorus compounds, nitrogen-based compounds and even certain metal and boron compounds. 

Organic compound Mineral fillers Resin (containing chloride) Catalyst (sometimes amine) Pigment... 

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene—propylene mbbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance (see Elastomers, ETHYLENE-PROPYLENE rubber). This is done by sequential polymerisation of homopolymer polypropylene and ethylene—propylene mbber in a multistage reactor process or by the extmsion compounding of ethylene—propylene mbber with a homopolymer. Addition of high density polyethylene, by polymerisation or compounding, is sometimes used to reduce stress whitening. In all cases, a superior balance of properties is obtained when the sise of the discrete mbber phase is approximately one micrometer. Examples of these polymers and their properties are shown in Table 2. Mineral fillers, such as talc or calcium carbonate, can be added to polypropylene to increase stiffness and high temperature properties, as shown in Table 3. 

Mineral fillers are used for light-colored compounds. Talc has a small particle size and is a semireinforcing filler. It reduces air permeabihty and has htde effect on cure systems. Calcined clay is used for halobutyl stoppers in pharmaceutical appHcations. Nonreinforcing fillers, such as calcium carbonate and titanium dioxide, have large particle sizes and are added to reduce cost and viscosity. Hydrated siUcas give dry, stiff compounds, and their acidity reduces cure rate hence, their content should be minimized. 

Blends of the polysulfone tesia have been made with ABS, poly(ethylene terephthalate), polytetrafluoroethylene (PTFE), and polycarbonate. These ate sold by Amoco under the Miadel trademark. Additional materials ate compounded with mineral filler, glass, or carbon fiber to improve properties and lower price. 

This is also known as Bulk Moulding Compound (BMC). It is blended through a mix of unsaturated polyester resin, crosslinking monomer, catalyst, mineral fillers and short-length fibrous reinforcement materials such as chopped glass fibre, usually in lengths of 6-25 mm. They are all mixed in different proportions to obtain the required electromechanical properties. The mix is processed and cured for a specific time, under a prescribed pressure and temperature, to obtain the DMC. 

Inorganic fillers in plastics compositions are usually in a very finely divided form and, as such, are ideal for powder XRD study. A sample size of a few mg gives a good pattern in 1 or 2 h. Crystalline mineral fillers can usually be observed directly in the complete polymeric formulation, in concentrations exceeding about 1 %. Combined XRD/XRF studies are favoured [326]. A mineral filler is easy to identify in a compound in the absence of other fillers. 

First introduced industrially in the 1930s, thermoplastic polymers are today produced and consumed in vast quantities and play a major role in many aspects of our everyday lives. It is estimated that over 16 million tons were consumed in Western Europe alone in 1991 [1]. Mineral fillers have, since the beginning, made an important contribution to the spectacular growth of thermoplastic polymers. The addition of mineral materials was initially seen mainly as a means of extending or reducing the compound cost but, as the relative cost of the polymers decreased, this became less important and attention was more and more focused on the property improvements that could be achieved. 

The need to minimise production costs and hence the selling price of mineral fillers is a dominant theme running through the technology. Although compound cost reduction was one of the principal reasons for using fillers in the past, this is of less importance now, due to the fall in the cost of the commodity thermoplastics. Indeed, the cost in use of fillers (taking into account volume costs and the cost of incorporation) can now lead to a rise in overall compound costs and it is often the minimisation of this cost increase that has become important. 

Mineral fillers have a marked influence on the compounding procedures used for thermoplastics processing. These must be chosen to ensure good dispersion, while producing minimum aspect ratio degradation when flbre or plate fillers are being used. 

Since the materials have a very soft plasticity rating, or inches of flow on spiral mold, the materials are all molded in special transfer molding presses and specially designed transfer molds. Because an acid catalyst and glass or mineral fillers are used to make the compound, these materials may have an adverse effect on the hardened steel mold with the result that there may be excessive runner and gate wear. 

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. 

Ebonite compounds shrinks to about 6% during cure and as such due allowance for a change of dimensions has to be made for this during manufacture. The ebonite dust and the mineral fillers added for controlling the exothermic reaction serves to reduce this shrinkage. 

At the present time aminoplasts comprise moulding compounds based on amine resins (thermosetting condensation products of formaldehyde with carbamide or melamine or a combination thereof) and organic or mineral fillers or a combination thereof doped with dyestuff and modifying substances (plasticizers, stabilizers, crosslinking agents, and the like). 

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