Glass-fibre composites unsaturated polyester

A pyrolysis technique was investigated as a method for the chemical recycling of glass fibre-reinforced unsaturated polyester SMC composites. The proeess yielded liquid products and gases and also a solid residue formed in the pyrolysis of glass fibres and fillers. The solid residue was used as a reinforeement/filler in unsaturated polyester BMC composites, and the influenee on mechanical properties was studied in comparison with BMC prepared entirely from virgin materials. 

Rot K, Huskic M, Makarovic M, Mlakar T L, Zigon M (2001) Interfacial effects in glass fibre composites as a function of unsaturated polyester resin composition Composites Part A, 32(3 ), 511-516. 

The chemical resistance of polyester amide glass fibre composite is excellent [126]. A solvent mixture of CF3COOH/CHCI3 was used as a solvent for thermotropic LC polyester, based on 4-chlorocarbonyl phenyl esters of aromatic dicarboxylic acids and phenols or aliphatic diols for viscosity measurement. This indicates thermal stability in various organic solvents. [127]. Unsaturated aromatic LC polyesters, synthesized with the aim to fix the LC state, can be crosslinked by using styrene. The crosslinked matrix can be degraded by refluxing in 3 M aqueous sodium hydroxide solution and methanol in a vol. ratio of 3 2 [128]. 

Finally, glass-reinforced unsaturated polyesters are well known as building materials for boats, yachts and cars and generally termed fibre-glass resin . The preparation, properties and applications of these unsaturated polyesters are summarized in Chapter 21, while the chemistry and properties of a new unsaturated polyester resin for fibre-reinforced composite materials are discussed in Chapter 22. 

The ribs were manufactured from FRP composites. The laminate used glass fibres in tissue form and rovings as additional reinforcement, embedded in a matrix of unsaturated polyester (PU) resin. A gel coating provides protection. 

By incorporating unsaturated dicarboxylic acids (e.g. maleic acid), besides phthalic acid, into the polycondensation reaction, unsaturated polyesters are formed. These are then cross-linked with a low-molecular unsaturated monomer, usually styrene, in the presence of a peroxide catalyst and a cobalt compound as accelerator. Unsaturated polyesters are applied as cast resins or glass fibre-reinforced composites. The latter product was the first large-scale plastic material in the self-extinguishing category for the building industry... 

Contact moulding is a simple and well known method for fabrication of fibre-reinforced thermoset composites. Thermoset resins which cure at room temperature such as unsaturated polyester, vinyl ester, and epoxy are used to make glass, jute or carbon fibre-reinforced composites using contact moulding. A wide variety of structures can be fabricated using this technique without limitation with respect to the size and complexity of the shape of the structure. However, the process is very labour-intensive and time-consuming, so is used only for a short run or one-off production. 

Krigbaum [12] has reported on the use of glass fibre reinforced composites, both from Cytec Industries, based on Cyglas 685 unsaturated polyester [bulk moulding compound (BMC)] and Cyglas 695 vinyl ester resin (BMC) in automotive valve covers and other engine cover applications. The recycling of these valve covers is also discussed. 

Vinyl ester resins (epoxy diacrylates) are used by the glass-fibre-reinforcement industry for products that are resistant to chemicals and corrosion. They are epoxy di(meth)acrylates (P-hydroxyester acrylates) that are usually obtained by reacting epoxy resins of glycidyl derivatives with (meth)acrylic acid. They can also be manufactured from bisphenol A and glycidyl (meth) acrylates (Kanerva et al. 1986 Kanerva et al. 1989 Jolanki 1991). Acrylates based on bisphenol A or epoxy resin can be polymerised by electron beams, ultraviolet light, and also by the addition of various peroxides (Jolanki et al. 1995). The same cross-linker (styrene), hardeners (organic peroxides) and accelerators (cobalt) as for unsaturated polyester resin are used in composite epoxy acrylates (Rolston 1980). 

In the case of glass fibre/unsaturated polyester matrix composites, the kinetic curve of weight changes can present a peculiar shape revealing the presence of osmotic cracking (see Fig. 12.23). Such behaviour can be explained as follows ... 

Dhakal HN, Zhang ZY, Bennett N. Influence of fibre treatment and glass fibre hybridisation on thermal degradation and surface energy characteristics of hemp/unsaturated polyester composites. Compos Part B 2012 43 2757-2761. 

Continuous-filament glass is widely used, alone or in hybrid composite structures with other fibres, in epoxy, unsaturated polyester, phenolic and melamine resins. Techniques for composite formation have already been outlined. In undirectional composites requiring high tensile strength and modulus, S-glass may be used because of its additional contribution to these properties. 

The low density of these fibres - about 0.97 g cm - means that in terms of specific stress and specific modulus (i.e. on a mass per unit length basis) they rank very highly. However, they are limited in composites by their low melting temperatures (about 140°C), tendency to creep, and the need for special surface-activation processes, such as corona discharge treatment, to develop adhesion to matrix polymers. They are sometimes used alone, but more often in hybrid yam and fabric stmctures with glass or carbon fibres in an epoxy or unsaturated polyester resin matrix to improve the impact resistance and energy absorption. Curing temperatures should not exceed 125°C. 

The use of accelerated ageing tests and spectrophotometric techniques in studying the photooxidative degradation of unsaturated polyester resins and glass fibre-reinforced composites is examined. Results of accelerated and natural ageing tests are compared, and criteria to be taken into account in achieving accelerated test results representative of reality are discussed. 5 refs. 

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