UV aging of poly(propylene)/wood‐fiber composites

Abstract

The effect of accelerated UV‐aging on properties of PP/wood‐fiber composites has been studied. Plates containing 0, 25 and 50 wt% wood‐fibers were subjected to accelerated UV‐aging in a QUV weatherometer for up to 8 weeks. Stabilization against UV‐degradation was made by adding 3% of a UV stabilizer. The results showed that both the unfilled PP and the PP/wood‐fiber composites displayed good UV resistance with regard to mechanical properties. The color of the PP/wood‐fiber composite plates changed from brown to chalky white at the exposed area because of the formation of a thin, strongly degraded surface layer. Physical and chemical analysis of these surface layers using differential scanning calorimetry, Fourier transform infrared spectroscopy, and scanning electron microscopy showed that degradation of the PP matrix had occurred, leading to chemicrystallization and extensive surface cracking. A decrease in PP melting temperature was also noted, due to molecular chain scission and the formation of extraneous groups, such as carbonyls and hydroperoxides. These results indicate that the wood‐fibers act as chromophores when incorporated in the PP matrix. Increasing the fiber content from 25 to 50 wt% increases the rate of degradation of the PP matrix by approximately a factor of two. Polym. Compos. 25:543–553, 2004. © 2004 Society of Plastics Engineers.

Wood plastic composites weathering: Visual appearance and chemical changes

“…Crazing of WPC may be caused by polymer chain scission, which results in highly crystallized polymer zones that crack and/or differentially contract (resulting from wetting and drying cycles) between the surface and interior sections during xenon-arc and exterior weathering. Surface cracks occurred around 400 h, and their frequency and size increased upon extended weathering, findings that are in agreement with the literature [12,31]. Densification of surface layers and spontaneous cracking of weathered PP may result from the scission of tie chain molecules in the amorphous phase that are released and then crystallized onto pre-existing crystals (a process known as chemicrystallization) [31].…”

“…The color changed from brown to chalky white, with the depth of degradation being approximately 0.5 mm. Seldé n et al [12] also reported that the degradation of the PP matrix resulted in a chalky appearance and extensive surface cracking. Falk et al [13] observed that PP-based composites faded at a higher rate than HDPE-based composites.…”

“…Falk et al [13] observed that PP-based composites faded at a higher rate than HDPE-based composites. In addition, degradation of PP-based WPC increased with an increase in wood content [12,13]. For HDPE-based WPC (50% wood content) color fade continued throughout 2000 h of weathering [14].…”

Effects of pigments on the UV degradation of wood‐flour/HDPE composites

“…The FTIR spectra of WF, HDPE, HDPE with 2% MAPE, and unweathered control samples of WF/HDPE composites are shown in Figure 3. Because the maleated coupling agents had no significant influence on the degradation of WPC, 16 its effect was not discussed here.…”

Performance of rice-hull-PE composite exposed to natural weathering

“…Peaks that appear in the spectra can be assigned to functional groups present at the composite surface. Thus, Oxidation at the degraded surface can be detected throughout weathering (Matuana et al 2001;Muasher and Sain 2006;Stark et al 2004a;Selde´n et al 2004;Colom et al 2000).…”