Thermoplastic-based composites

In addition to the advantages of the composite plate over the traditional graphite plate mentioned before, the carbon/carbon composite plates have the advantage of lower densify (about 30% lower than the thermoset- or thermoplastic-based composite plates [16]) and higher manufacturing efficiency. This offers the potential of continuous production in comparison with the machining process for graphife plates. 

Thermoplastic-based composite plate is another major type of composite plate with the thermoplastic matrix. The major advantage of this type of plafe is fhaf fhe well-developed injection molding processing in the thermoplastic industry can be used to manufacture the plates for saving cosf and improving production efficiency. 

In general, due to the simpler manufacturing process and the cheaper polymer matrix, the thermoset- or thermoplastic-based composite plates have lower cost than that of carbon/carbon composite plates. The thermoset-based composite and thermoplastic-based composite plates have their own advantages and limitations, which are largely determined by the properties of the matrix materials and the ratio between the filler and mafrix. 

The other difference [21] is fhaf fhermosef composife shows higher balanced sfrength and toughness compared to thermoplastic composite, with a little brittleness. Thus, thermoset composite plates can be fabricated relatively thinner and have more applications. On the other hand, as mentioned before, a well developed injection molding process has been applied as the fabrication process of thermoplastic-based composite plates to assure high quality and low cost. 

To achieve the goal of required performance, durability, and cost of plate materials, one approach is improvement of the control of the composition and microstructure of materials, particularly the composite, in the material designing and manufacturing process. For example, in the direction of development of thermoplastics-based composite plate, CEA (Le Ripault Center) and Atofina (Total Group) have jointly worked on an irmovative "microcomposite" material [33]. The small powders of the graphite platelet filler and the PVDF matrix were mixed homogeneously by the dispersion method. The filler and matrix had a certain ratio at the microlevel in the powder according to the optimized properties requirements. The microcomposite powders were thermocompressed into the composite plate. 

Creep due to thermal deformation restricts thermoplastic-based composites from structural uses. However, creep in thermoplastic-based composites may be controlled through crosslinking chemical reactions or surface plasma modifications. 

The laminar character of the flow is violated in thermoplast and thermoplast-based compositions flow throught the channels at high volume consumption rates. In extrusion formation processes this leads to undesired distortion of the extrudate... 

It is very important to understand non-isothermic kinetics to analyse the composition s technological properties, especially at very high sp s of cooling, which occur in thermoplasts and thermoplast-based compositions processing. The method for describing and forecasting non-isothermic crystallization kinetics is proposed in Ref [59]. Alternative methods for describing kinetics are in the studies cited in Ref [59] (see also Refs. [66, 67]). The essence of the method in Ref [59] is as follows. 

It is of interest to describe the function axo(t) analytically. This was done in [59] on the assumption that isothermic crystallization kinetics of thermoplasts and thermoplast-based compositions is described by the Kholmogorov-Avrami Equation (17). Let us write down Eq. (17) in a different way ... 

Through the processes of thermoplasts and thermoplast-based compositions are substantially non-isothermic. Therefore, variation of thermophysical proj ies is an important method of target regulation of filled thermoplasts technological properties. Utilization of mineralorganic materials as fillers for thermoplasts has great jxjtential in this sphere. 

U.S. Pat. Nos. 6,344,504 [102] and 6,498,205 [103] (both by Crane Plastics Company, TimberTech) disclose a thermoplastic-based composite, comprising at least 16% by weight of a powdered thermoplastic material, at least 50% by weight of cellulosic material, and a lubricant, a phenolic resin, and a compound containing one or more isocyanate groups, each of at least 1% by weight. A powdered thermoplastic material comprises polyethylene, LDPE, polypropylene, ethyl-vinyl acetate (EVA), and polyethylene copolymers. 

PVC-based composites, nnlike many other thermoplastic-based composites, are natural fire-resistant materials (see Chapter 2). Their FSl is in the range of 25-60 (Table 14.4), in Class A-B range. However, PVC also often employs flame retardants, mainly ATH, for fnrther decrease in its flammability. 

Extrusion and injection-moulding are the economically most attractive processing methods of thermoplastic-based composites. The extrusion press processing (express-processing) has been developed for the production of flax fibre reinforced PP at the research centre of Daimler Benz [7]. In this process, flax fibre non-wovens and PP melt films are alternatively deposited and moulded. A production process for PP semi-products reinforced with lignocellulosic fibres in the form of mats has been developed by BASF AG [7]. Fibre mats are produced by stitching together layers of fibres which have previously been crushed. 

Figure 1 Alternative manufacturing routes for thermoplastic-based composites and thermoplastic polymers (modified from [1]).

As the end use of AM parts has evolved from prototypes to marketable and functional components, developments have focused efforts on application-specific demands. Recent studies have reported usage of other thermoplastics and thermoplastic-based composites to obtain components with improved thermal or mechanical properties or even enhanced biodegradability (Table 7.3). 

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