Fibre polyethylene

In 1956, polyethylene fibres were prepared and later on polypropylene fibres were prepared. Fibres have been made from polytetrafloroethylene for special uses. 

Polyethylene fibres are handicapped by their low melting temperature. They are used for antiballistic products. 

Table 2. Laser-Raman spectrum of oriented polyethylene fibres...

Fig. 4. Raman spectra of a highly oriented polyethylene fibre. The meaning of the three experiments, shown here is evident from Ref. 10. Full line and broken line indicate electric vector of the laser beam perpendicular and parallel to the fibre axis, respectively. "Sp" spurious emission from the laser...

Van Dingenen JLJ, "Gel-spun high-performance polyethylene fibres", in Hearle JWS (Ed), "High-performance Fibres ", The Textile Institute and Woodhead Publishing Ltd, Abington, Cambridge, 2001, Chap. 3. 

The results obtained by drawing gel spun polyethylene fibres at different tempe-... 

Fig. 48. Linear strength-diameter relationship as observed for ullraoriented high molecular weight polyethylene fibres. With permission of the publishers Pergamon Press Inc. (Q...

Solution processing also plays a vital role in the manufacture of high value, lyotropic high modulus fibres and also high modulus polyethylene fibres. In all these cases the additional cost and complication of solvent recovery is offset by the high value of the produced product. 

The polyethylene fibre is produced by either high pressure polymerisation of ethylene with a peroxide-catalysed process or low pressure polymerisation of ethylene using new catalysts systems. The molecular structure of polyethylene is a linear polymer of ethylene units with repeat unit of... 

Creep. One of the most remarkable aspects of the deformation of polydiacetylenes is that it is not possible to measure any time-dependent deformation or creep when crystals are deformed in tension parallel to the chain direction (14,24). This behviour is demonstrated in Figure 3 for a polyDCHD crystal held at constant stress at room temperature and the indications are that creep does not take place at temperatures of up to at least 100 C (24). Creep and time-dependent deformation are normally a serious draw-back in the use of conventional high-modulus polymer fibres such as polyethylenes (28). Defects such as loops and chain-ends allow the translation of molecules parallel to the chain direction in polyethylene fibres. In contrast since polydiacetylene single crystal fibres contain perfectly-aligned long polymer molecules (cf Figure lb) there is no mechanism whereby creep can take place even at high temperatures. 

Recently elastic polyolefin fibres have also been introduced (generic name lastol), they are cross-linked and stable at temperatures up to 220 °C and above.- High-tenacity polyethylene fibres, with ultra high molecular weight (UHMW-PE, Dyneema) have been available for some time they are produced by a gel-spinning process at high dilution. 

The results obtained by drawing gel spun polyethylene fibres at different temperatures are shown in Fig. 5. It can be seen that the relationship between Xmax, and >-1/2 predicted by Eq. (3) holds to a good approximation. Furthermore, the intercept at = 1 for a draw temperature of 90 °C was found to be 3.8, in good agreement with the value of 3.7 estimated above. The higher values of gel at higher temperatures were attributed to chain slippage. 

Ahmed, S.F.U., Maalej, M. and Paramasivam, P. (2006). Flexural responses of hybrid steel-polyethylene fibre reinforced cement composites containing high volume fly ash. Journal of Construction and Building Materials, 21 1088-1097. 

Although this author claims no special expertise in the toxicology of materials, it seems fair to say that the weight of opinion at present is reassuring about fibres in existing use. Glass, aramid and polyethylene fibres are all much safer than asbestos. In common with traditional materials such as wood and cotton, they must always be handled with care, especially if they are finely divided and therefore in respirable forms, i.e. small (<3 pm) diameter short fibres or fine dust. 

R Frissen, L Govaert and T Peijs, ModelUng of the baUistic impact behaviour of polyethylene-fibre reinforced composites . Proceedings ICCM-10, Whistler, BC, Canada. Cambridge, Woodhead, 1995, Volume 5, pp 759-766. 

Polyethylene fibres are made by several different processes and their thermal characteristics vary, but lack of high temperature resistance is very noticeable compared with other reinforcing fibres. Most polyethylene fibres begin to lose their mechanical properties at about 120°C and they melt soon afterwards. 

High performance polyethylene fibres such as Dyneema (a reinforcing polyethylene fibre from DSM) show a pronounced time-dependent behaviour under static loading conditions. An increase in strain rate and/or decrease in temperature results in an increase in fibre modulus and strength, but a decrease in work of fracture [33]. It is also known that creep can be observed even in unidirectional PE-fibre reinforced laminates. How far this specific behaviour influences the fatigue behaviour is of great interest and has to be investigated in order to find the appropriate applications for PE-composites. 

A A J M Peijs, High Performance Polyethylene Fibres in Structural Composites, Doctoral Thesis, Technical University, Eindhoven, 1993. 

A A J M Peijs, P Catsman, L E Govaert and P J Lemstra, Hybrid composites based on polyethylene and carbon fibres. Part 2 Influence of composition and adhesion level of polyethylene fibres and mechanical properties . Composites 1990 21 513. 

The experimental data for oriented polyethylene fibres and films (see for example Ref. 10) are consistent to a first approximation with this simple interpretation, provided that we add an additional isotropic second moment contribution to take into account the dipolar interactions external to the proton pairs (Fig. 4). 

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