UHMWPE fibers

It is interesting to note that the simple Morse potential model, when employed with appropriate values for the parameters a and D (a = 2.3 x 1010 m 1, D = 5.6 x 10 19 J as derived from spectroscopic and thermochemical data), gives fb = 6.4 nN and eb = 20%, which are quite comparable to the results obtained with the more sophisticated theoretical techniques [89]. The best experimental data determined on highly oriented UHMWPE fibers give values which are significantly lower than the theoretical estimates (fb 2 nN, b = 4%), the differences are generally explained by the presence of faults in the bulk sample [72, 90] or by the phonon concept of thermomechanical strength [15]. 

Fig. 5,22. Schematic illustration of UHMWPE fiber s structural hierarchy. After Ward (1985).

Interface shear bond strength of epoxy droplets on a UHMWPE fiber"... 

Fig. 5.2,. Scunning cicciron micropholographs of (a) untreated and (b) plasma treated (120 s) Tekmilon UHMWPE fibers. After Tissington et al. (1991). Reproduced by permission of Chapman Hall.

In the previous sections, techniques developed for improving the interface bond quality are discussed mainly for glass, carbon, aramid and UHMWPE fibers with... 

Polymers of MMA, AAc, and MAA were grafted onto an ultrahigh molecular weight polyethylene (UHMWPE) fiber surface after pretreatment with electron beam irradiation [31]. Sundell et al. [32] pretreated a PE film with electron beams to facilitate the graft polymerization of vinyl benzylchloride onto the substrate. The inner surface of porous PE hollow fiber had also been modified by grafting of glycidyl methacrylate (GMA) polymer after electron beam irradiation [33]. 

The focus in this chapter will be on the two main polyolefin polymers, namely polyethylene (PE) and polypropylene (PP). The latter especially has established itself as a very versatile fiber with unique applications in the textile and nonwoven industry. Polyethylene, on the other hand, has not been widely used as a fiber compared to other synthetic polymers such as PET, PP, and nylon, due in part to its low melting point. This chapter will, however, discuss ultra-high molecular weight polyethylene (UHMWPE) fiber that given its success and uniqueness in the synthetic fiber industry. 

UHMWPE fibers are used in apphcations such as marine cordage and hfling slings, police and military ballistic vests, armored vehicles, cut-resistant gloves, fishing lines, and safety clothing. 

Orientation prior to extraction of oil from gel filaments can also produce fibers. The flexible and random chains of linear polymers can be successfully drawn into highly oriented and extended conformations. Total draw ratios up to 350 have been obtained in the laboratory (23). This so-called gel spun UHMWPE yields the highest specific tensile properties of any polymeric fiber. Systematic studies (24,25,26) of gel spun UHMWPE fibers have reported a maximum tensile modulus of220 GPa and maximum tensile strength of 6.0 GPa. 

In addition to para-aramid and UHMWPE fibers, other types of polymer have also been developed for nse in bullet-proof applications. Table 10.1 (Herakovich, 1998) summarizes the current high-performance polymer fibers. It shoirld be mentioned that there still exists a big gap in mechanical properties between the commercial fibers and the theoretical values, as shown in Table 10.2 (Herakovich,... 

Fig. 10.7 (Ruan et al., 2006) depicts the typical stress-strain curves of the 5 wt% MWCNT/UHMWPE composite fiber and the pure UHMWPE fiber at a draw ratio of 30 measured at room temperature using a MTS RT/5 micro tester with a load cell of 10 N at room temperature and an elongation rate of 25 mm/min. The 5 wt% MWCNT/UHMWPE fiber shows tensile modulus of 137 GPa, tensile strength of 4.2 GPa and strain at break of 4.7 per cent, representing enhancements...

Stress-strain curves for the highly oriented 5wt% MWCNT/ UHMWPE composite and pure UHMWPE fibers at DR = 30 (Ruan... 

The interfacial load transfer during the stress-strain deformation of the 5 wt% CNT/UHMWPE composite fiber is shown in terms of Raman shift at different deformations at a draw ratio of 30. Raman shift versus strain for the asymmetric C-C stretching band of PE (1060cm ) and the G-band (1595 cm ) of CNT inside the 5wt% MWCNT/UHMWPE composite fiber at a draw ratio of 30 are depicted in Figs 10.8(a) and 10.8(b), respectively. The Raman shift of the pure UHMWPE fiber at a draw ratio of 30 is also shown in Fig. 10.8(a) for comparison. The data are divided into three regions. In region I, the G-band shows a rapid... 

Raman shift versus strain for the asymmetric C-C stretching band of PE (1060cm ) (a) and the G-band (1595cm ) (b) of CNT inside the 5wt% MWCNT/UHMWPE composite fiber at draw ratio = 30. The Raman shift of the pure UHMWPE fiber at draw ratio = 30 is also shown. 

Table 10.3 Comparison of mechanical properties of various commercial high-performance fibers (Kim and Mai, 1998) and 5wt% MWCNT/UHMWPE fiber (Ruan etai, 2006)...

Ruan, S., Gao, P. and Yu, T. X. Ultra-strong gel-spun UHMWPE fibers reinforced using multiwalled carbon nano tubes. Polymer 1006, 47 1604-11. 

The tensile strength of UHMWPE fiber (Spectra 1000) is in the range of 2.9-3.7 GPa. This compares well with that of high-carbon steel (1.2 GPa). Multiwalled carbon nanotubes, however, have even higher tensile strength of over 60GPa ... 

Figure 3.17. Epitaxial structures on UHMWPE fiber obtained after annealing at 130°C. [Adapted, by permission, from McDaniel, P B Deitzel, J M wayS...

Figure 3.17 shows epitaxial growth on the surface of UHMWPE fiber. " Interesting is that the growth is homoepitaxial. " There are several reason which may cause epitaxial crystallization, as follows " ... 

Highly oriented flexible-chain polymers, in particular ultrahigh-molecular-weight polyethylene (UHMWPE) fibers prepared by gel spinning process, as suggested by Smith and Lemstra [322], exhibit the extremely high mechanical strength and modulus of elasticity rather close to the theoretical estimates. At the same time, these fibers reveal decreased creep resistance which substantially restricts their application potential. 

Highly oriented gel-crystallized UHMWPE fibers contain macrofibrils whose length reaches tens and hundreds of microns as aggregates of microfibrils of micrometer length macrofibrilles form layers separated by longitudinal voids of submicron and micron scale [312]. Figure 78a shows that the creep jumps with deformation steps of 1-10 and about 100 microns are observed in this case. In fact, meso-jumps are formed from micro-jumps similar to formation of macrofibrils from... 

Fig. 78 Dependence of the creep rate (at e 2% on the creep increment (a) for oriented gel-crystallized UHMWPE fibers with draw ratio X = 45 (creep rate jumps of large strain periods L 100 jam are observed), and (b) for the same fibers chemically modified for generating crosslinks between fibrils (the large strain periods are absent) [313]...

The above results evidence the controlling role of interfibrillar slippage for creep properties of UHMWPE fibers. 

Because the excellent mechanical properties of UHMWPE fiber are the result of high drawn ratio during the fiber processing, evident fibrils are often found on the surface of the high-performance fibers, as shown in Fig. 2.24. 

Table 20.3 Resulting UHMWPE Fiber/Epoxy Resin Interfacial Shear Strength (IFSS) After XeCI Laser Treatment of the Fibers Under Different Conditions [129]...

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