Thermal properties fibres

For the electricity electronics markets. Table 2.18 displays the performances and costs of six engineering thermoplastics reinforced with glass fibres and UL94 VO rated. The designer can choose between four levels of costs, five levels of water absorption and several levels of mechanical and thermal properties according to the requirements. 

These fibres are used for their thermal properties combined with high mechanical performances. Unfortunately, their price is prohibitive and applications are reduced to, for example, rocket motors. 

With optimum selection of fibres and matrices, favourable residual stress conditions can be established in the matrix, which lead to increased A Tc. Above A Tc, matrix cracks appear but the presence of crack-deflecting fibre-matrix interfaces ensures minimal effect on mechanical properties as the fibres remain largely unaffected. As damage is also confined mostly to the surface of the materials, changes in mechanical and thermal properties are more readily identified by means other than mechanical testing. 

This chapter has reviewed the performance of CMCs under conditions of thermal shock. It has been shown that CMCs exhibit superior resistance to thermal shock, compared with their monolithic counterparts, as catastrophic failure can always be avoided. Resistance to higher temperature differentials and property retention after the onset of thermal shock cracking (especially in fibre-reinforced CMCs) can be realised, provided that the mechanical and thermal properties of CMCs are optimised by careful choice of their constituents. 

Providing flame retardancy for fibre blends has proved to be a difficult task. Fibre blends, especially blends of natural fibres with synthetic fibres, usually exhibit a flammability that is worse than that of either component alone. Natural fibres develop a great deal of char during pyrolysis, whereas synthetic fibres often melt and drip when heated. This combination of thermal properties in a fabric made from a fibre blend results in a situation where the melted synthetic material is held in the contact with the heat source by the charred natural fibre. The natural fibre char acts as a candle wick for the molten synthetic material, allowing it to bum readily. This can be demonstrated by the LOl values of cotton (18-19), polyester (20-21) and a 50/50 blend of both (LOl 18), indicating ahigher flammability of the blend as described later (Section 8.11). But a rare case of the opposite behaviour is also known (modacrylic fibres with LOl 33 and cotton in blends from 40-60 % can raise the LOl to 35). 

Wrzesniewska-Tosik, K. Tomaszewski, W. Struszczyk, H. Manufacturing and thermal properties of lignin-based resins. Fibres Textiles in Eastern Europe 2001, 9 (2), 50-53. 

PP/silver nanocomposite fibres were prepared with the aim of achieving permanent antibacterial activity in a common synthetic textile. The fibres were melt-spun by coextmsion of PP and PP/silver masteibatches using general conjugate spinning. Masteibatches were made up of a mixture of PP chips and nano-sized silver powder. The antibacterial efficacy of spun fibres was high when the masteibatch was used as the sheath rather than the core. The antibacterial activity of nano-silver in fibres was evaluated after a certain contact time and calculated by percent reduction of two types of bacteria. Staphylococcus aureus and Klebsiela pneumoniae. DSC and wide-angle X-ray diffraction were used for analysis of stractuie, thermal properties and crystallisation behaviour of the spun fibres. SEM was carried out in order to observe particle distribution on the nanocomposite fibres. 17 refs. (2nd International Conference on Polymer Fibres, Manchester, UK, July 2002)... 

A microcalorimeter scan can also be used to provide a determination of the nature of meats [34]. As shown in Figure 21, samples of chicken breast and thigh show different profiles which may be due to differences in their pH and contraction state as well as different content of red and white muscle fibres. It is also important to consider whether the material is examined in isolation versus in situ because the thermal properties may be different. 

Physical and thermal properties Bakelite is a thermoset, hard, brittle material. Its high shrinkage on moulding and brittleness are mediated by adding fillers or reinforcing fibres. It resists burning. 

Physical and thermal properties Polyesters are formed via a condensation reaction. PET and poly(butylene terephthalate) (PBT) are not crosslinked so are thermoplastic, but cured polyesters are crosslinked and thermosets. Polyesters may be reinforced with glass or carbon fibres or particles. Addition of 30% or more carbon fibre induces electrical conductivity in polyesters. Despite its high polarity, PET Is a good electrical insulator at ambient conditions because its Tg is considerably higher than room temperature. Polyesters have good abrasion resistance and are tough. PET is impervious to water but has low permeability to oxygen. 

Improved stiffness, strength and thermal properties are offered by beta-Ti alloys reinforced with silicon carbide fibres. A high probability exists that these composites will make their way into the design of the actively cooled airframe of the future US NASP X30 spaceplane. 

Much has been written over the past years on the topic of properties of textiles and some other materials comprising sport garments, which affect the manufacture and physical attributes of clothing. A considerable amount of the debate involves transport of liquid water, water vapour and thermal properties. This debate continues, particularly with respect to refinements of existing fibre types, the creation of different fabric structures, and the application of new finishes and coatings, many of which are... 

Majumdar, A., Mukhopadhyay, S., Yadav, R., 2010. Thermal properties of knitted fabrics made from cotton and regenerated bamboo cellulosic fibres. Int. J. Therm. Sci. 49 (10), 2042-2048. 

Polyester resins are easy to work with. They have viscosities at room temperature of between 300-700 mPas, which is sufficiently low to allow fast and efficient wet out of the glass fibres. They cure well at room temperature to afford acceptable mechanical and thermal properties and resist a wide range of dilute chemicals at moderate temperatures. They are cheap, varying in price from approximately 2-3DMkg ... 

S.H. Aziz, M.P. Ansell, The effect of alkalization and fibre alignment on the mechanieal and thermal properties of kenaf and hemp bast fibre composites part 1-polyester resin matrix. Compos. Sci. Technol. 64(9), 1219-1230 (2004)... 

AUi AUiuthali, A., Low, I. M., Dmig, C. Characterisation of the water absorption, mechanical and thermal properties of recycled cellulose fibre reinforced vinyl-ester eco-nanocomposites. Composites Part B - Eng. 43 (2012) 2772-2781. 

Carbon and aramid fibres are anisotropic with different values of mechanical and thermal properties in the main directions, whereas glass fibres are isotropic (Eckold 1994). 

The LC polymers comprise mesogenic groups either in the backbone or in side chains, as indicated in Figme 12. They form a stable state of matter. These polymers are attractive because they combine typical properties of low molecular hquid crystals with mechanical and thermal properties of macromolecular materials, that is they can be processed to fibres or films and we can fi eeze in the LC state. 

Recycling has a dramatic influence on the mechanical and thermal properties of unstabilised polyamide 66. However, glass fibre reinforced polyamide 66 may be recycled up to four times without any significant deterioration in the performance of the material. Proper amounts and combinations of processing additives and antioxidants, together with optimised processing parameters, make it possible to recycle polyamides without significant losses of mechanical properties. 

---