Chemically crosslinked polyethylene: Modulus‐temperature relations and heat stability

Abstract

SynopsisThe influence of M T black concentration on the shear podulus of low-density crosslinked polyethylene can be approximated by the Guth-Gold equation, at temperatures below the crystalline melting zone. Above the melting zone shear modulus does not depend practically on the carbon black level. At high temperatures both degradation and crosslinking reactions are taking place. The variation of the shear modulus with temperature due to these reactions is shown for various carbon black loadings. A preliminary chemical stress-relaxation study a t 250°C is presented. INTRODUCTIONCarbon black is a useful filler for polyethylene compounds; however, only low black concentrations can be added to the thermoplastic polymer since higher loadings result in irderior properties. Crosslinking of the polyethylene-black compound by irradiation or chemical means permits the incorporation of higher black concentrations. The black is tightly bound in the polymeric network and cannot be removed by refluxing samples in good polyethylene solvents. Only in the case of insufficient crosslinking doas the solution become black due to partial carbon black separation.The properties of unloaded crosslinked low-density polyethylene do not differ appreciably from the properties of the original polyethylene at room temperature.lT2 This phenomenon is due to the rather low degree of crosslinking actually achieved and to the relatively small decrease in crystallinity content as a result of crosslinking. The main differences between the thermoplastic and crosslinked polyethylene are found at temperatures above the crystalline melting point where the crosslinked polymer behaves as a soft rubber, while the thermoplastic polyethylene has no significant strength above the melting temperature.The incorporation of carbon black alters the properties over the whole temperature range. The brittle point and yield stress increase with the black concentration.s Carlson4 has shown from stress-strain measurements at room temperature that the modulus increases arid elongation decreases with increasing black content. The tensile strength at 302°F was found to increase with the black concentration, while at room temperature tensile strength was practically u~iaffected.~ These results show that the role of

Rheological properties of polyethylenes modified with dicumyl peroxide

“…In determining A, we have used the values of Mw given in Tables IV and V, and have calculated the density p ( T ) , using the following expression: (5) = 26.768 + 2.05 x in which T is absolute temperature ( O K ) . Note that eq.…”

“…s + so. 5 Figure 3 gives molecular weight distribution (MWD) curves of the LDPE-A before and after reacting with dicumyl peroxide. The following observations may be noted in Figure 3: (1) the modified LDPE-A has more high molecular weight portions compared to the virgin resin.…”

Resistivity‐temperature behavior of carbon fiber filled semicrystalline composites

“…This could well result in reformation of the conductive paths; consequently, the resistance of the composite will decrease, giving rise to the NTC behavior. For the crosslinked composite, crosslinking mainly occurs at the amorphous region,29, 32, 33 where CFs are dispersed as mentioned in the previous subsection. 3 CFs are strongly attached to crosslinked networks, and thus the agglomeration of CF and the NTC effect can be effectively eliminated.…”

Transparent Conductive Films Fabricated from Polythiophene Nanofibers Composited with Conventional Polymers

“…On the other hand, conductive nanofiller/polymer composite materials have attracted great academic and industrial attention, as they offer high conductivity in a conventional flexible polymeric film [13][14][15][16][17], and various new materials have been developed to satisfy market needs, exhibiting for example, specific thermal [18][19][20][21][22][23][24][25], mechanical [26,27], and electrochemical properties [28−36] in addition to conductivity. There are several different types of conductive nanofillers, including carbon nanotubes [18][19][20][21][22][23][24][28][29][30][31][32][33][34][35][36], carbon fibers [26], metal particles [25], and conductive polymers [37,38].…”

“…There are several different types of conductive nanofillers, including carbon nanotubes [18][19][20][21][22][23][24][28][29][30][31][32][33][34][35][36], carbon fibers [26], metal particles [25], and conductive polymers [37,38]. Our aim in the present work was to solve the problems associated with the P3HT nanofiber mat as a transparent, conductive film by using the nanocomposite technique.…”