Transparent wood composite, systems and method of fabrication

Abstract

Highly transparent (up to 92% light transmittance) wood composites have been developed. The process of fabricating the transparent wood composites includes lignin removal followed by index-matching polymer infiltration resulted in fabrication of the transparent wood composites with preserved naturally aligned nanoscale fibers. The thickness of the transparent wood composite can be tailored by controlling the thickness of the initial wood substrate. The optical transmittance can be tailored by selecting infiltrating polymers with different refractive indices. The transparent wood composites have a range of applications in biodegradable electronics, optoelectronics, as well as structural and energy efficient building materials. By coating the transparent wood composite layer on the surface of GaAs thin film solar cell, an 18% enhancement in the overall energy conversion efficiency has been attained.

What is being claimed is: 
     
         1 . Wood-based light transmitting system, comprising:
 a wood block pre-cut from a natural wood at a predetermined angular relationship to a direction of natural internal channels in said natural wood and treated to remove lignin therefrom, thus forming a lignin-devoid wood block, said natural internal channels having walls formed of cellulose-containing material; and   a filling material having refraction index substantially matching the refractive index of said cellulose-containing material of said natural internal channels' walls, and substantially fully infiltrating said natural internal channels in said lignin-devoid wood block with said filling material, thereby forming a transparent wood composite member.   
     
     
         2 . The wood-based light transmitting system of  claim 1 , wherein said transparent wood composite member has an upper cut plane and a bottom cut plane, and wherein said predetermined angular relationship constitutes an angle of approximately 90° between said direction of said natural internal channels and at least one of said upper and bottom cut planes of said transparent wood composite member. 
     
     
         3 . The wood-based light transmitting system of  claim 1 , wherein said transparent wood composite member has an upper cut plane and a bottom cut plane disposed in a direction substantially coinciding with said direction of said natural internal channels in said transparent wood composite member. 
     
     
         4 . The wood-based light transmitting system of  claim 1 , wherein said filling material includes at least one of materials selected from a group consisting of:
 Thermosetting polymers, including Polyester fiberglass, Polyurethanes polymers, Vulcanized rubber, Bakelite, Duroplast, Urea-formaldehyde, Melamine resin, Diallyl-phthalate (DAP), Polyimides and Bismaleimides, Cyanate esters or polycyanurates, Furan resins, Polyester resins, Silicone resins, Benzoxazine resins, Bis-Maleimides (BMI), Cyanate ester resins, Epoxy (Epoxide) resins, Phenolic (PF) resins, Polyester resins, Polyimides, Polyurethane (PUR) resins, Silicone Resins, Vinyl ester resins,   Thermoplastic polymers, including Acrylic, ABS, Nylon, PLA, Polybenzimidazole, Polycarbonate, Polyether sulfone, Polyetherether ketone, Polyetherimide, Polyethylene, Polyphenylene oxide, Polyphenylene sulfide, Polypropylene, Polystyrene, Polyvinyl chloride, Teflon, and   Cellulose derivatives, including, Cellulose acetate, Cellulose acetate butyrate, Cellulose triacetate, Methyl cellulose, Hydroxypropyl methyl cellulose, Ethyl cellulose, Hydroxyethyl cellulose, Carboxymethyl cellulose, Dissolved cellulose, Nanofibrillated cellulose, Cellulose nanocrystals,   functional index matching materials, such as, for example, liquid crystal, pressure/temperature sensing materials, piezoelectric materials,   colorless polymer nano-glue, transparent liquid epoxy resin precursor with low viscosity, a mixture of a resin and non-blushing cycloaliphatic hardener, polyvinylpyrrolidone (PVP), Poly(methyl methacrylate) (PMMA), Poly(vinyl alcohol) (PVA), and Polydimethylsiloxane (PDMS).   
     
     
         5 . The wood-based light transmitting system of  claim 1 , wherein said transparent wood composite member is configured as a block having a length and width, respectively, of approximately 1 mm and larger, and a thickness of approximately 100 μm and larger. 
     
     
         6 . The wood-based light transmitting system of  claim 1 , wherein said transparent wood composite member has light transmittance ranging approximately from 80% to 95% and optical haze ranging approximately from 80% to 100% in the visible light wavelength range from 400 nm to 1100 nm. 
     
     
         7 . The wood-based light transmitting system of  claim 1 , wherein the refractive index of said filling polymer is approximately 1.53 at a light wavelength λ=550 nm. 
     
     
         8 . The wood-based light transmitting system of  claim 1 , wherein said wood-based light transmitting system further includes an optoelectronic system including at least one of photonic systems, solar cells, photo-detectors, displays, and wide-angle lighting systems having advanced light management. 
     
     
         9 . The wood-based light transmitting system of  claim 8 , wherein said at least one of the solar cells includes an optically active layer and said at least one transparent wood composite member shaped as a layer having a thickness ranging between 100 μm and 3 mm, and disposed in optical contact with said optically active layer. 
     
     
         10 . The wood-based light transmitting system of  claim 1 , wherein said transparent wood composite member exhibits high mechanical strength with a fracture strength of 23.5-45 MPa and higher and high ductility, and wherein said wood-based light transmitting system includes light-harvesting building structures. 
     
     
         11 . A transparent wood composite, comprising:
 a wood block of predetermined dimensions pre-cut from a natural wood in a predetermined angular relationship to a direction of natural internal channels of said natural wood and treated to form a lignin-devoid wood block, said natural internal channels in said wood block having walls formed of natural cellulose-containing material, and   a filling polymer substantially completely infiltrating said internal channels in said lignin-devoid wood block and cross-linked with said cellulose-containing material of said internal channels' walls in said wood block, wherein said filling polymer has refractive index substantially matching the refractive index of said natural cellulose-containing material of said internal channels' walls.   
     
     
         12 . The wood-based light transmitting system of  claim 11 , wherein said wood block is configured with an upper cut plane and a bottom cut plane spaced apart each from another by a pre-determined distance ranging approximately between 100 μm and 14 mm, and wherein at least one of said upper and bottom planes extends in crossing relationship with said natural internal channels or substantially therealong. 
     
     
         13 . The wood-based light transmitting system of  claim 11 , wherein said filling polymer has refractive index approximating to 1.48. 
     
     
         14 . The wood-based light transmitting system of  claim 13 , wherein the refractive index of said filling polymer is approximately 1.53 at the light wavelength of λ=550 nm. 
     
     
         15 . The wood-based light transmitting system of  claim 11 , wherein said filling polymer includes at least one of the polymers selected from a group consisting of:
 Thermosetting polymers, including Polyester fiberglass, Polyurethanes polymers, Vulcanized rubber, Bakelite, Duroplast, Urea-formaldehyde, Melamine resin, Diallyl-phthalate (DAP), Polyimides and Bismaleimides, Cyanate esters or polycyanurates, Furan resins, Polyester resins, Silicone resins, Benzoxazine resins, Bis-Maleimides (BMI), Cyanate ester resins, Epoxy (Epoxide) resins, Phenolic (PF) resins, Polyester resins, Polyimides, Polyurethane (PUR) resins, Silicone Resins, Vinyl ester resins,   Thermoplastic polymers, including Acrylic, ABS, Nylon, PLA, Polybenzimidazole, Polycarbonate, Polyether sulfone, Polyetherether ketone, Polyetherimide, Polyethylene, Polyphenylene oxide, Polyphenylene sulfide, Polypropylene, Polystyrene, Polyvinyl chloride, Teflon, and   Cellulose derivatives, including, Cellulose acetate, Cellulose acetate butyrate, Cellulose triacetate, Methyl cellulose, Hydroxypropyl methyl cellulose, Ethyl cellulose, Hydroxyethyl cellulose, Carboxymethyl cellulose, Dissolved cellulose, Nanofibrillated cellulose, Cellulose nanocrystals,   functional index matching materials, such as, for example, liquid crystal, pressure/temperature sensing materials, piezoelectric materials,   colorless polymer nano-glue, transparent liquid epoxy resin precursor with low viscosity, a mixture of a resin and non-blushing cycloaliphatic hardener, polyvinylpyrrolidone (PVP), Poly(methyl methacrylate) (PMMA), Poly(vinyl alcohol) (PVA), and Polydimethylsiloxane (PDMS).   
     
     
         16 . A method of fabrication of a wood-based light transmitting system, comprising:
 (a) pre-cutting a wood block from a natural wood in a pre-determined angular relationship to natural internal channels of the natural wood, the natural internal channels having walls formed from cellulose-containing material and being filled with lignin,   (b) removing the lignin from natural internal channels of said wood block, thus forming a lignin-devoid wood block, and   (c) sequentially infiltrating said natural internal channels in said lignin-devoid wood block with a filling polymer having refractive index substantially matching a refractive index of said cellulose-containing material of the internal channels' walls.   
     
     
         17 . The method of  claim 16 , further comprising:
 in said step (b), preparing a lignin removal solution by mixing a solution of NaOH in deionized water, and a solution of Na 2 SO 3  in deionized water,   boiling said pre-cut wood block in said lignin removal solution for approximately 12 hours,   rinsing said pre-cut wood block in hot distilled water, and   boiling said rinsed pre-cut wood block in a bleaching solution containing solution of H 2 O 2  in distilled water until a color of the pre-cut wood block disappears, thereby obtaining a lignin-devoid wood block.   
     
     
         18 . The method of  claim 16 , further comprising:
 in said step (c), immersing said lignin-devoid wood block in said filing polymer in the liquid phase thereof,   degassing said liquid filing polymer under pressure of 200 Pa for approximately 5-10 minutes to remove a gas and ethanol solvent from the lignin-devoid wood block,   applying the atmosphere pressure to the liquid filling polymer to promote the internal channels infiltration process,   repeating said atmosphere pressure application a predetermined number of times, thus obtaining the polymer infiltrated wood block immersed in the liquid filling polymer,   maintaining the polymer infiltrated wood block in said filling polymer undisturbed at approximately 30° C.-60° C. for approximately 12 hours until the liquid filling polymer solidifies, and   removing said polymer infiltrated wood block from the solidified filling polymer, thus obtaining said transparent wood composite member.   
     
     
         19 . The method of  claim 16 , further comprising:
 fabricating a solar cell including an optically active layer,   depositing ethanol on a surface of said optically active layer,   placing said transparent wood composite member on said optically active layer in contagious contact therewith, thus forming a sandwich structure, and   drying the sandwich structure containing said transparent wood composite member coupled to said optically active larger at room temperature to firmly attach said transparent wood composite member to the solar cell.   
     
     
         20 . The method of  claim 16 , further comprising:
 attaching said transparent wood composite member to a building at a site of at least one of a window and a roof.