Fibres dimensional stability

Typical applications for nylon include small gears, bearings, bushes, sprockets, housings for power tools, terminal blocks and slide rollers. An important design consideration is that nylon absorbs moisture which can affect its properties and dimensional stability. Glass reinforcement reduces this problem and produces an extremely strong, impact resistant material. Another major application of nylon is in fibres which are notoriously strong. The density of nylon is about 1100 kg/m. ... 

Traditionally carpet tile backings have been made from bitumen, PVC or polyurethane. There are problems with the environmental impact of these materials and they are difficult to recycle. Shaw industries developed their EcoWorx carpet tile backing using a polyolefin resin. This has superior environmental profile to PVC and is easier to recycle than bitumen and the cross-linked polyurethane backings. EcoWorx has lower toxicity, better adhesion and good dimensional stability. It is easy to recycle and can be separated from any fibre type used in the carpet tile. It works particularly well with nylon-6 fibres. EcoWorx tiles contain 40% recycled content and Shaw have established a collection and return scheme to close the loop. 

Polyurethane fibres (Perlon U) were prepared by reacting hexamethylene disocyanate with 1,4 butanediol in 1942. Because they were difficult to dye and had harsh feel so went out of the market. But these resins are used for small mechanical components like gears and bearings because of dimensional stability and retention of electrical resistance in humid conditions. 

Research on resin-bonded boards has used wood chips, or fibres, that are acetylated prior to composite manufacture. In almost all cases, acetylation has been achieved by using uncatalysed acetic anhydride. Significant improvements in dimensional stability proportional to the WPG of the wood particles have been reported when acetylated wood is used, and there is also a reduction in irreversible swelling (e.g. Bekere etal., 1978 Arora etal., 1981 Rowell etal., 1986a-e, 1989, 1990, 1991,1995 Yoshida etal., 1986 Youngquist etal., 1986a,b, 1988 Larsson and Tillman, 1989 Subiyanto etal., 1989 Vick etal., 1991 Clemons etal., 1992 Kajita and Imamura, 1993 Sasaki and Kawai,... 

Rowell, R.M., Kawai, S. and Inoue, M. (1995). Dimensionally stabilized, very low density fibre-board. Wood and Fiber Science, 27(4), 428—436. 

Uprating PVC compounds often involves the careful specification and addition of mineral fillers. This article discusses calcium carbonate, talc and glass fibre, taking into account their size and their shape factor. Rigidity is sensitive to the shape factor of the filler as is the dimensional stability. This study shows that glass fibre is the most efficient filler. Talc is more efficient than calcium carbonates. The impact performance is very sensitive to the particle size. Precipitated calcium carbonate is the only filler to act as an impact modifier. 12 refs. 

Alkyd Excellent dimensional stability and heat resistance, surfaces tough, good susceptibility to fillers and fibres. 

Crease resistance and dimensional stability are imparted both by polymer formation within the fibre and by building cross-links between adjacent cellulose chains. It has been known for a long time that formaldehyde will react with cellulose. 

Fillers may be divided into particulate and fibrous types. Particulates include calcium carbonate, china clay, talc and barium sulphate. Fillers affect shrinkage on moulding and the dimensional stability of the finished plastic, increase tensile strength and hardness, enhance electrical insulation properties and reduce tackiness. They also impart opacity and colour (Figure 3.16). Carbon black is now the most widely used filler for polymers usually in the form of furnace carbon black, which has a particle diameter of 0.08 mm. Fibrous fillers reinforce polymers and greatly increase their tensile strengths. They include fibres of glass, textile and carbon. Plastics filled with fibrous fillers are known as composites. 

Fibre choice is complex where cost often outweighs performance. For industrial composites, E glass therefore dominates. In aerospace, where cost can be spread over a longer life, often with savings in maintenance and service, carbon and other high-performance fibres are selected. For example, the high-modulus carbon fibres provide the highest dimensional stability of satellite dishes, where performance is critical. 

Also polydimethylsiloxane (PDMS) emulsions and micro-emulsions are well known as conditioners in textile finishing imparting softness, dimensional stability and wrinkle and stretch recovery. When combined with quats and esterquats they improve the water absorbency of softened cotton fabric. Long-chain PDMS with amino- or amido-functional side groups anchor the silicone to the fibre by way of attractive electrostatic forces. Interfibre friction is reduced in this way, producing a distinct and substantive softener effect. ... 

Glass matrix composites, in particular with carbon fibre reinforcement, have been also proposed for a variety of applications which require thermal dimensional stability, i.e. materials with multidimensional near zero thermal expansion coefficients such as support structures for laser mirrors [21, 22]. 

The fabric substrate used for the filter media will need to provide certain characteristics, dependent on the application. The typical properties required include abrasion resistance, stretch resistance, dimensional stability, and resistance to flex fatigue. All these performance criteria can be assessed by using suitable test methods. The fabric will also be tested for correct warp and weft sett, air permeability, thickness, density, and fabric tensile properties. All the factors will affect the performance of the filter as they are directly related. If woven fabrics are considered, the porosity will be directly related to the sett and therefore air permeability. The combinations of the fibre types, fabric constructions, and coating substrate will provide the filter manufacturer with a range of properties for use in a range of appUcations. 

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