Polyethylene weight change

The polyethylene film thus obtained was packed in a 100 mesh stainless steel basket, extracted with hot p-xylene in a Soxhlet extractor for 48 hours, washed with acetone for 4 hours in the same type extractor, dried in vacuum for 20 hours at 40°C and weighed. The gel fraction (Gf) of the polymer was detrmined by the equation (2) from the weight change by the extraction. 

Figure 6. Weight change of medium density polyethylene as a function of time following immersion in 1,1,1-trichloroethane...

TABLE XII Qualitative expression of effects on high density polyethylene of changes in melt flow rate, density, and distribution of molecular weight... 

For high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and PP combinations of phenolic antioxidants and phosphites lead to a synergistic protection of the polymer. For HDPE and LLDPE an increased amount of phosphite provided increased processing stability at constant phenol concentration. A 4 1 ratio of phosphite to phenol exhibited the best performance, while the most efficient ratio for protecting melt flow of the PP was found when a 2 1 ratio of phosphite to phenol was added [167], According to Parrondo molecular weight changes can best be reduced with phenolic antioxidants, while phosphites prevent discoloration [168]. 

Kumnayaka, T.O., Parthasarathay, R., Jollands, M., et al. Molecular weight changes during photo-oxidation of polyethylene nanocomposites. Korea-Aust. Rheol. J. 22, 173-177 (2010)... 

HDPE melts at about 135°C, is over 90% crystalline, and is quite linear, with more than 100 ethylene units per side chain. It is harder and more rigid than low density polyethylene and has a higher melting point, tensile strength, and heat-defiection temperature. The molecular weight distribution can be varied considerably with consequent changes in properties. Typically, polymers of high density polyethylene are more difficult to process than those of low density polyethylene. 

Fig. 15. Dynamic stiffness images of alternating layers of polyethylene (PE) of two molecular weights at (a) 105 Hz and (b) 200 Hz. The contrast is due to changes in contact compliance (1/stiffness) of the nanoindenter probe in contact with each of the two polymers. The probe-sample respon.se (1/stiffness) as a function of frequency shown in (c) is consistent with the dynamic stiffness images.

At 300°C and in the presence of KOH an increase in the molecular weight is observed, i.e., the reaction of macropolymerization is realized [38,39]. Potassium hydroxide is effectively inhibiting thermal destruction of polyethylene at temperatures from 350-375°C. The per cent change in molecular weight is half or one-third as high as that without the use of an inhibitor. At 400°C the efficiency of inhibition is insignificant. Potassium hydroxide with an ABC carrier is effective up to the temperature of 440°C due to the increased contact surface of the inhibitor with macroradicals. 

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