Abstract
Surface photostability strongly influences the usefulness of bamboo and bamboo-based polymer composites in outdoor environments. In this study, accelerated aging tests were conducted to investigate how UV irradiation affects the color, surface appearance, and chemical characteristics of outdoor bamboo-fiber-reinforced composite (OBFRC) prepared from moso bamboo (Phyllostachys pubescens Mazel) by a three-step process involving phenol-formaldehyde (PF) resin impregnation. The surface color of natural bamboo (NB) changes rapidly during irradiation, but that of OBFRC remains relatively stable: densification mitigates the negative effects of UV irradiation. More generally, OBFRC exhibits enhanced surface photostability caused by structural and chemical modifications.
Highlights
Published: 7 April 2021Moso bamboo (Phyllostachys pubescens Mazel) contains a naturally occurring polymeric composite composed of cellulose, hemicellulose, and lignin
The sensitivity of lignin to light with wavelengths shorter than 400 nm [3] can result in the formation of free radicals by its stantial negative correlation is noted between I1507 /I898 and ∆E*, whereas a positive correlation is noted between I1730(1728) /I898 and ∆E*, indicating that the surface photochromism of natural bamboo (NB) and outdoor bamboo-fiber-reinforced composite (OBFRC) during UV irradiation is closely related to the degradation of lignin and the resulting formation of carbonyl groups
The enhancement mechanism of the surface photostability of OBFRC was primarily due to the compaction of bamboo cells and the protective effect of PF resin
Summary
Moso bamboo (Phyllostachys pubescens Mazel) contains a naturally occurring polymeric composite composed of cellulose (approximately 55%), hemicellulose Of the molecular components of bamboo, lignin is the most sensitive to UV light [2], which acts on the phenolic hydroxyl group of lignin to form free radicals These free radicals are subsequently transformed into unsaturated carbonyl compounds (o- and p-quinonoid structures) by demethylation or side chain cleavage [3], causing surface yellowing of the bamboo [2]. The application of clear coatings containing a combination of organic/inorganic UV absorbers has been demonstrated to be effective in inhibiting the surface photodegradation of bamboo, while preserving its aesthetic characteristics as much as possible [13]. Acetylation treatment does not provide wood with long-lasting photoprotection [16], and the limited concentration of phenol-formaldehyde (PF) resin in the structure does not prevent lignin from being photodegraded. The effects of structural modification and the presence of PF resin on the photodegradation behavior of OBFRC are investigated
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