Forming of reinforced plastics

As a result, when they are used to reinforce plastics, significant increases in modulus (with talc and mica) and strength (with mica only) can be obtained at little or no increase in cost. There is also a further advantage over fibres when platelets are aligned parallel to each other (as they are in the surface layers of an injection moulding) they provide reinforcement in all directions in their plane, not merely in one direction as with uniaxially aligned fibres. 

When a component is manufactured from a reinforced plastic, the forming process does more than simply shape the component it also positions the reinforcing particles, and fixes their orientation. This results in an important characteristic of a reinforced polymer its structure usually has directionality, and it shows anisotropy in its physical properties. Moreover, the material is usually inhomogeneous, as the particle orientation and even degree of reinforcement may vary from point to point throughout a component. 

The platelet reinforcements in common use are all minerals. Two in particular are notably successful talc and mica. Talc in a magnesium silicate, while mica is an aluminium silicate. 

Mica K2O 3AI2O 6Si02 2H2O (muscovite form) 

Typically of naturally occurring materials, they are never obtained in pure form. The product of one mine always differs from that of another, because of the presence of varying proportions of contaminating minerals. 

The success of mineral platelet reinforcements is due to their desirable combination of cost and properties  

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High performance composites may be laminates wherein veils of carbon fiber ate treated with an epoxy resin, stacked up to the desired final product thickness, and then laminated together under heat and pressure (see Composite materials Carbon and graphite fibers). Simply mixing together carbon or glass fibers and polymeric resins to form a reinforced plastic leads to a composite material, but this is not a laminate if not constmcted from discrete phes. 

Glass fibres are the principal form of reinforcement used for plastics because they offer a good combination of strength, stiffness and price. Improved... 

Glass in the form of fibres is relatively inexpensive and is the principal form of reinforcement used in plastics. The fibres are produced by drawing off continuous strands of glass from an orifice in the base of an electrically heated platinum crucible which contains the molten glass. The earliest successful glass reinforcement had a calcium-alumina borosilicate composition developed... 

Chemical compounds that contain methylol groups (-CH2 OH) form stable, covalent bonds with cellulose fibers. Those compounds are well known and widely used in textile chemistry. Hydrogen bonds with cellulose can be formed in this reaction as well. The treatment of cellulose with methylolmelamine compounds before forming cellulose unsaturated polyesters (UP) composites decreases the moisture pickup and increases the wet strength of reinforced plastic [48,49]. 

So if ACh is involved in memory function, what does it do Any attempt to answer that question has to follow some consideration of how memory is thought to be processed. Many neuroscientists believe that memory is achieved by changes in the strength of synaptic connections (activation) between neurons and that increases in such synaptic activity somehow reinforce the pattern of neuronal activity during the memorising of an event so that it can be more easily restored later. One form of such plasticity is longterm potentiation (LTP), which has been mostly studied in the hippocampus where, as in other areas associated with memory, there is the appropriate complex synaptic morphology. 

By far the most common form of reinforcement is fiberglass. Products using unsaturated polyester resin as a matrix and fiberglass fiber reinforcements are commonly referred to as composites , laminates or FRPs (fiber-reinforced plastics). The latter reinforcements are sold as continuous roving, which is continuously chopped in place with a liquid resin stream, chopped roving mat, woven... 

Sheet is thermoformed into a product by one of the forming process. To reinforce or rigidize it, one side that is usually the back surface of the formed sheet receives a spray-up of reinforced plastic (Chapter 15). 

Diallyl phthalate is used as a monomer as well as in prepolymer form in the preparation of reinforced plastics. Diallyl itaconate is also used as a cross-linking agent for unsaturated polyester resins as well as in cross-linking of vinyl copolymers. 

Repeated rapid heating of reinforced plastics articles which have previously absorbed moisture or solvents causes various forms of damage to the composite, related to the absorbed liquids. 

Chemical compounds which contain reactive groups such as the methanol group (-CH2OH) as in methanolamine compounds are able to form stable, covalent bonds with cellulose fibres. This treatment decreases the moisture pick-up and increases the wet strength of reinforced plastics. Isocyanates are also suitable to modify the chemical structure via its reaction with the OH groups of cellulose. The mechanical properties of composites reinforced with wood-fibre and PVC or PS can be improved by an isocyanate treatment of those cellulose fibres or the polymer matrix. The improvement of the properties of the composites can be explained by the reduction in the number of OH groups responsible for moisture uptake and consequently the increase in the hydrophobicity of the fibre s surface... 

Figures 8-3, 8-4 and 8-5 show some of the parts which incorporate the sandwich panel concept to improve stiffness. They range from structural foam molded parts (which come from the mold as completed parts) incorporating low density cores and high density skins of the same materials to parts vacuum formed of a plastics material, the core of which becomes cellular during the heating process for forming. Reinforced plastic structural panels for curtain wall building construction that have honeycomb cores or decorative cores are examples...

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