The influence of short branches on the α, β and γ‐relaxation processes of ultra‐high strength polyethylene fibers

Abstract

Dynamic mechanical measurements were conducted for several kinds of ultra–high‐strength polyethylene fibers with different methyl branch contents. As is the case with conventional polyethylene materials, UHSPE fibers also exhibit α, β, and γ‐relaxation dispersions. Each relaxation process is the function of both the tensile moduli and the branch contents of UHSPE fibers. It was also found that the γ‐process of UHSPE fibers is dominated mainly by the localized molecular motion in the crystalline part, such as a dislocation mode of crystallite defects, which is very sensitive to the branching content. From the time and temperature superposition of the frequency dispersion experiments, it was found that activation energies for both the α2‐process and α3‐process increase proportionally to the methyl branch content, while the α1‐process is not so affected by the branch content. This result shows that the incorporated branch sites in the crystalline part effectively hinder the chain‐to‐chain slippage; meanwhile, they have not hindered the slippage at the grain boundary so far, which also enables us to explain the creep improvement of UHSPE fibers through branch incorporation with the same mechanism. © 1994 John Wiley & Sons, Inc.

Thermo-viscoelastic and viscoplastic behavior of high-density polyethylene

“…Fig. 7 demonstrates that the apparent activation energy of HDPE far below the melting temperature is about 78 kJ/mol, which is lower than the values provided in some studies grounded on the standard method of superposition of observations in dynamic tests: E a ¼ 110-140 (Zamfirova et al, 2002), E a ¼ 137 (Pegoretti et al, 2000), E a ¼ 150-170 (Mano et al, 2001), E a ¼ 174 (Djokovic et al, 2000), and E a ¼ 207 kJ/mol (Tajvidi et al, 2005), but agrees well with the activation energies E a ¼ 50-140 (Stadler et al, 2005), E a ¼ 65-80 (Boiko et al, 1995), E a ¼ 79-106 (Matsuo et al, 1988), and E a ¼ 89 kJ/mol (Ohta and Yasuda, 1994). The fact that the apparent activation energy of HDPE in the solid state exceeds that of HDPE melt by twice [in the latter case, the activation energy belongs to the interval between 27 and 32 kJ/mol (Bin Wadud and Baird, 2000)] appears to be natural, whereas rather high values of the activation energies (close to the activation energies for thermal degradation of this polymer [E a ¼ 210-270 (Sinfronio et al, 2005) and E a ¼ 260-290 kJ/mol (Marazzato et al, 2007)] ''shows that the physical significance of E a .…”

Fabrication of Tunable Submicro‐ or Nano‐Structured Polyethylene Materials from Immiscible Blends with Cellulose Acetate Butyrate

“…Crystalline structure of LDPE nanofibers were also determined using DSC at a heating rate of 10 °C · min −1 under nitrogen atmosphere and wide angle X‐ray diffractometer (WAXD), as shown in Figure 7 and 11, respectively. Figure 7 shows an endothermic shoulder around 70 °C in all thermograms, which was a result of the α ‐relaxation of PE involving the molecular mobility within the crystalline phase 25, 26. The melting temperatures were almost the same for all samples, with peaks around 111 °C.…”

Influence of the Main-Chain Configuration on the Mechanical Properties of Linear Aliphatic Polyesters

“…Indeed, for PE with 12.5 methyl branches/1000 methylene units an increase of activation energy of the α c -relaxation was observed from 147 to 227 kJ·mol −1 , which was ascribed to the hindrance of chain-to-chain slippage. 36 To summarize, even though ester groups do not appear to have a significant effect on the crystalline structure, irregular stacking of the ester groups seems to increase the crystal mobility, thereby lowering the yield stress of the associated polymer.…”