Study on the Structure of Peroxide Cross-Linked Polyethylene Pipes with Several Stabilizers

Abstract

Cross-linked polyethylene (PEX) pipes used in hot water supply are required for high mechanical strength and high creep resistance at high temperature. Especially PEX-a pipes which are made by peroxide cross-linking have better performance, such as creep resistance and thermal shock resistance than the pipes made by the other cross-linking method. Because the PEX-a pipes indicate the higher cross-link degree as compared with the other PEX pipes. In this study, the PEX-a pipes which were mixed with several stabilizers were tested to evaluate the effects on cross-link degree and the oxygen induction time. And also they are evaluated with the chlorine aqueous solution by the performance of the long-term hydrostatic pressure test and the long-term hydro dynamic pressure test. As a result, it was found that the combination of antioxidants for PEX-a pipes plays an important role to prolong the oxygen induction time without inhibiting the cross-linking. From the results of the 1 H pulsed NMR measurement over the melting point of polyethylene, it was found that each peroxide PEX pipe with different antioxidant combinations indicated the different proportion and crosslink density of cross-linked region, in addition, that these pipes had the effective structure of cross-linking for the hydrostatic and hydrodynamic pressure test with the chlorine aqueous solution. Therefore, it was considered to be useful results for studies of the stricture of cross-linking of polyethylene.

Silane Crosslinked Polyethylene from Different Commercial PE’s: Influence of Comonomer, Catalyst Type and Evaluation of HLPB as Crosslinking Coagent

“…As the degree of crosslink increases, segmental motion is progressively restricted until in, for example, phenolic, amino or epoxy resins, only infusible, rigid, amorphous state exists [1][2][3] . Polyethylene crosslinking may be induced through three different methods: radiation, peroxide and silane [4][5][6][7][8] . In peroxide crosslinking, organic peroxide and polyethylene are blended during extrusion process and free radicals are formed, crosslinking the polymer chain to produce a network during thermal decomposition 9 .…”

P1.2 - Determination of the Degree of Cross-linking and Curing with Single-sided NMR

“…Due to cross-linking the degrees of freedom of molecules in amorphous regions are reduced by the formation of a network and a change in relaxation times occurs. The feasibility to correlate NMR relaxation with the degree of cross-linking and curing has already been shown [6,7,8,9].…”

Single-sided NMR for the measurement of the degree of cross-linking and curing

“…Due to cross-linking the degrees of freedom of molecules in amorphous regions are reduced by the formation of a network and a change in relaxation times occurs. The feasibility of correlating NMR relaxation with the degree of cross-linking and curing has already been shown (Dole, 1979;Fry and Lind, 1988;Hirabayashi et al, 2013;Netto, 2014).…”

“…Relatively long measurement times for a quantitative result and the destructive character of these standard test methods inhibit a 100 % process monitoring. There are already initial efforts to realize process measurements by other methods, such as rheological tests (Heiduk et al, 2015).…”