Surface chemistry changes of weathered HDPE/wood-flour composites studied by XPS and FTIR spectroscopy

Abstract

The use of wood-derived fillers by the thermoplastic industry has been growing, fueled in part by the use of wood-fiberthermoplastic composites by the construction industry. As a result, the durability of wood-fiber-thermoplastic composites after ultraviolet exposure has become a concern. Samples of 100% high-density polyethylene (HDPE) and HDPE filled with 50% woodflour (WF) were weathered in a xenon arc-type accelerated weathering apparatus for 2000 h. Changes in surface chemistry were studied using spectroscopic techniques. X-ray photoelectron spectroscopy (XPS) was used to verify the occurrence of surface oxidation. Fourier transform infrared (FTIR) spectroscopy was used to monitor the development of degradation products, such as carbonyl groups and vinyl groups, and to determine changes in HDPE crystallinity. The results indicate that surface oxidation occurred immediately after exposure for both the neat HDPE and WF/HDPE composites; the surface of the WF/HDPE composites was oxidized to a greater extent than that of the neat HDPE. This suggests that the addition of WF to the HDPE matrix results in more weather-related damage. The results also show that while neat HDPE may undergo crosslinking in the initial stages of accelerated weathering, WF may physically hinder the ability of HDPE to crosslink, resulting in the potential for HDPE chain scission to dominate in the initial weathering stage.

Competitive and synergistic effects between excimer VUV radiation and O radicals on the etching mechanisms of polyethylene and fluoropolymer surfaces treated by an atmospheric He–O2post-discharge

“…The oxygenated functions detected in the case of the He post-discharge are attributed to the dissociation of the ambient O2 by interacting with the post-discharge. In both cases, the decomposition of the C 1s peak demonstrates the existence of four components: C-C (or C-H), C-OH, O-C-O (or C=O) and O-C=O, appearing at the following binding energies 285.0 eV, 286.5 eV, 288.0 eV and 289.5 eV [40]. These four components were also detected by decomposing the C 1s peaks measured on the aluminum foils (see table 1).…”

A review on the degradability of polymeric composites based on natural fibres

“…At low sisal content (<20%), the sisal fibre acts as a nucleating site, increasing crystallinity. However, when the sisal content is above 20%, crystallinity decreases as the fibre begins to hinder the molecular motion of polypropylene [59]. Composites experienced more lightening and mechanical properties loss when exposed to UV radiation with water spray cycle compared to UV radiation cycle alone [29,30].…”

“…In contrast, crosslinking does not affect polymer crystallinity. While chain scission occurs in the amorphous phase of the polymer and is controlled by the diffusion of oxygen in this region, UV-induced crosslinking occurs in imperfect crystalline regions [59].…”

“…Study on accelerated weathering of WPC by Stark et al [59] shows that while neat HDPE may undergo crosslinking in the initial stages of accelerated weathering, wood fibre (WF) may physically hinder the ability of HDPE to crosslink, resulting in the potential for HDPE chain scission to dominate in the initial weathering stage up to 1000 h before decreasing. At this point, chain scission begins to affect the tie molecules, resulting in a net decrease in crystallinity.…”

“…X-ray photoelectron spectroscopy (XPS) was used to verify the occurrence of surface oxidation by studying the concentration of carbon to oxygen atoms through equation 3 [59]:…”