Hot compaction technology

While one solution to producing very stiff and strong products is to incorporate fibers in a resin matrix up to a fiber volume fraction of about 65 wt%, another technology, based on heating and compacting fibers drawn from the same TP material, can be performed. This procedure has been used to fabricate different products such as plastic packaging PP and PE papers and boards. 

Property Unit PP60 1/1 balance weave PP 75 1/1 PET 65 1/1 balanced weave PP604/1 PP75 unidirectional TRE/PP SMC 

High modulus melt-spun PE from Hoechst Celanese Certran has a modulus of about 40 GPa (common unreinforced engineering TPs have a modulus in the range 2.3 to 3 GPa) showed a longitudinal modulus of 37 GPa for unidirectional fiber and 110 MPa longitudinal strength, a transverse modulus of 3.9 GPa and transverse strength 28 MPa. The process continues to be applied to all melt-spun fibers. 

Other fiber configurations include chopped fibers, woven cloth, and laminates of unidirectional fibers. The process allows a light tough and highly stiff RP to be manufactured using only one phase of the material, which has considerable advantages over two-component RPs. 

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As well as PET, Hine et al. showed that polyethylene naphthalate (PEN) could also be a candidate material for the hot compaction process by demonstrating that bi-directional composites could out-perform hot compacted PET composites, especially at elevated temperatures [149]. Bfine and Ward also reported the application of the hot compaction technology to woven fabrics of nylon 6,6 fibres, which, like PET fibres, are readily available in a variety of commercial forms [76]. 

Alcock et al. [161], presented in Fig. 14, show that although the mechanical properties of the reinforcement phase are much lower than for the other reinforcements presented here, the efficiency of retention of reinforcement properties in these final composites is higher. This was achieved by the use of the hot compaction technology by Rasbum et al. [135] and the coextruded tape technology by Alcock et al. [161] to obtain high volume fractions of reinforcement, combined with careful processing conditions to retain the molecular orientation (and so high mechanical properties) of the reinforcement phase in both cases. 

Gallivan V.L., G.K. Chang, and D.R. Horan. 2011a. Practical implementation of intelligent compaction technology in hot mix asphalt pavements, journal of the Association of Asphalt Paving Technologists, Vol. 80, p. 1. 

Ward I M, Hine P J and Norris K (1992) Polymeric materials, British Patent GB 2253420. Ward I M and Hine P J (2004) The science and technology of hot compaction. Polymer 45 1413-1427. 

After completing the preheating sequence and once the even heating of the semifinished stack has been accompHshed, the actual (hot) compaction phase begins. If necessary, from a process-technological point of view, the pretempered semifinished stack is inserted into the pressing unit and is subjected to heat and the necessary compaction pressure. In order to enable a selective melting of the films, tapes or fibers, it is essential to differentiate... 

FVom a process-technological point of view, thermoforming previously hot-compacted semifinished PP-plate products proves to be the simpler option. The semifinished plate pro-... 

A clear, processing-technological differentiation to the previous hot-compaction can be made and is based upon the tempering of the shaping tool, which possesses a temperature that is far below the hot-compaction temperature or that is at room temperature. The preheated, self-reinforced semifinished plate products are inserted into a cold cavity and formed under pressure. This procedure allows relatively short cycles at low molding ratios. 

Ward IM, Hine PJ (2004) The science technology of hot compaction. Polymer 45 1413-1427 Wei W, Minullina R, Abdullayev E, Fakhrullin R, Mills D, Lvov Y (2014) Enhanced efficiency of antiseptics with sustained release from clay nanotubes. RSC Adv 4 488-494 White HM, Bassett DC (1998) On row structures, secondary nucleation and continuity in a-polypropylene. Polymer 39 3211-3218... 

Most published work that has been identified as describing forming of self-reinforced polymer composites has been performed on PP-based systems, because, to date, these systems have received most attention as possible commercial products. Self-reinforced polymer composites based on the hot compaction concept reported by Ward and coworkers at the University of Leeds [33] have been commercialised into a product branded as Curv (formerly by BP Amoco, later by Propex Fabrics, USA) [225]. The use of coextruded PP tape technology, as reported by Peijs and coworkers [5], has been commercialised and branded as PURE (by Lankhorst Pure Composites, The Netherlands) [226], and also licensed to Milliken and Company, USA who market the material as Tegris (formerly as MFT) [227, 228, 270]. An apparently similar composite technology based on coextruded PP tapes has also been commercialised as Armordon (by Don and Low, UK) [229]. 

This technology (16, 17) produces sulphur concrete blocks by a manufacturing process very different from a hot poured sulphur concrete system. Solid sulphur, aggregate, liquid and a mineral binder are mixed together cold and compacted into a mold. Because of the presence of the small amount of liquid and mineral binder, the product retains its shape, although at this point the sulphur is not binding the product together in any way. The block is then dried to remove the liquid and heated in an oven to melt the sulphur. 

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