Guamuchil wood (Pithecellobium dulce) subjected to oxidation processes to increase transparency

Abstract

The increasing demand for sustainable and transparent materials in construction has intensified interest in alternatives to conventional glass, which is known for its energy-intensive production, high carbon emissions, brittleness, and environmental impact. This study focuses on guamuchil wood (Pithecellobium dulce), recognized for its rapid growth, high hardness, and adaptability to arid environments, as a candidate for transparent wood applications. Unlike traditional delignification, which can damage wood, the photooxidative method used here preserves its integrity by partially modifying the wood under milder conditions. Thus, this study explores the enhancement of guamuchil wood transparency through a photooxidative process, an approach not previously applied to this species. Visual analysis revealed a progressive increase in transparency of guamuchil wood with UV exposure, reaching maximum clarity at 10 h (GW10) due to extensive chromophore degradation. Exposure beyond this point led to undesirable yellowing due to excessive oxidation. SEM analyses revealed the photooxidative treatment of guamuchil wood-induced cell wall thinning, increased cell diameter, and enhanced structural order. EDS showed a reduction in carbon content from 44.16 to 42.14% and an increase in oxygen content from 55.84 to 57.86%, indicating partial degradation of lignin. FTIR analysis confirmed these oxidative changes, showing decreased aromatic lignin peaks and increased hydroxyl and carbonyl signals, with lignin content reduced from 27.5 to 21.9%. The water contact angle decreased from 62.4° to 12.2°, reflecting increased surface hydrophilicity due to lignin degradation and the exposure of hydroxyl groups. These changes contributed to a substantial improvement in optical transmittance, rising from ~ 6% in untreated wood (GW0) to 19% in GW10 at 7 mm thickness, achieved without polymer infiltration. This demonstrates the effectiveness of the photooxidative process in enhancing transparency through selective lignin degradation and surface modification. This study demonstrates a novel photooxidative process to enhance guamuchil wood transparency, achieving significant optical improvement without polymer infiltration. The process selectively degrades lignin, offering a sustainable alternative to glass in construction with reduced environmental impact.