Iranian Journal of Wood and Paper Industries

Iranian Journal of Wood and Paper Industries

Investigation of the effect of wood species on the optical properties of transparent wood composites with polyvinyl alcohol and epoxy polymers

Document Type : Research Paper

Authors
Hamideh Abdolzadeh 1
Alireza Kangarloo 2
Seyed Mahmoud Mir Tari 2
1 Shahid Rajaee Teacher Training University,Tehran, Iran
2 Shahid Rajaee Teacher Training University, Tehran, Iran
10.22034/ijwp.2025.2068027.1719
Abstract
Problem Statement and Objectives: Wood has long been used as a construction material. In recent years, various wood-based products, with an emphasis on their aesthetic properties, have attracted significant attention from researchers. Transparent wood composite, commonly referred to as transparent wood in the industry, is one such product. Transparent wood is an emerging optical material that combines properties such as haze and high light transmission with construction applications. Transparent wood composites are produced by delignifcation of wood or deactivating the chromophores in lignin and infiltrating it with a polymer that has a refractive index equal to or similar to that of cellulose. This product integrates mechanical performance with optical capabilities, making it a promising candidate for applications such as smart buildings, optical devices, and photonics. This study investigates the preparation methods and optical performance of transparent wood and discusses its potential applications.
Methodology: In this study, two wood species, beech and maple, were used to produce transparent wood composites after delignification. Delignification of wood veneers was carried out using sodium chlorite (NaClO₂) at a pH of 4.6. The delignified samples were impregnated with epoxy resin (E) and polyvinyl alcohol (PVA) under vacuum conditions. Polymerization of PVA resin was conducted at 40°C in an oven, while epoxy resin was polymerized at ambient temperature. The transparent wood composites were tested for optical properties according to the ASTM 1003-21 standard. Wood veneers, delignified veneers, and transparent polymers made from pure epoxy and PVA resins were used as control samples for comparison. In this study, light transmission values were examined as the determining factor for the transparency and haze of transparent wood composites. Three replicates were measured for each sample, and the average values were compared.
Results: Optical tests conducted on control samples showed that wood veneers did not transmit light and lacked haze. The delignified samples of both species, despite noticeable color changes, also lacked optical transparency. Consequently, no reportable values were obtained due to the lack of complete transparency in these samples. The results indicated that, unlike solid wood and its delignified veneers, the produced transparent wood composite exhibited suitable optical transparency and transmitted light. Optical tests revealed that transparent wood composites not only transmitted light but also had higher haze compared to transparent polymers. The light transmission in transparent wood made from beech species with epoxy resin and polyvinyl alcohol decreased by 43.17% and 7.85%, respectively. The haze of transparent wood from the beech species was more suitable and increased by up to 671%. The light transmission values showed no significant difference between the two species. Samples made with epoxy resin exhibited higher transparency compared to PVA resin. Images from scanning electron microscopy confirmed the filling of cavities and changes in cell walls after delignification.
Conclusion: The results demonstrated the feasibility of producing transparent wood composites. The beech species exhibited better light transmission and haze. Transparent wood composites possess suitable opacity characteristics, making them ideal for use in partition spaces or windows, enabling the utilization of sunlight while providing conditions for maintaining privacy. The results from both species were satisfactory, with the composite made from epoxy resin exhibiting superior properties.
Keywords
Transparent wood
optical properties
delignification
Haze and transmission
Subjects
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Iranian Journal of Wood and Paper Industries
Volume 17, Issue 1
Spring 2026
Pages 21-33