Study And Optimization Of Aluminum Phosphate Adhesives For Plywood

The continuous influx of formaldehyde bonded products emanating from various wood industries remains a concern due to the possible emission of hazardous volatile organic compounds.Apart from this,the use of petrochemical-based products is not sustainable.The carcinogenic substances emitted from formaldehyde could cause human discomfort.This encourages the development of environmentally friendly and sustainable products like aluminophosphate adhesives through the hybridization of various organic and inorganic materials.The recent findings showed that organic-inorganic wood adhesives possessed excellent bonding properties to replace formaldehyde adhesives.Compared to formaldehyde adhesives,aluminophosphate adhesives are more beneficial for fabricating wood-based panels due to their cost-effectiveness,sustainability,and environmental friendliness.However,aluminophosphate adhesives possessed weak bonding properties in moisture-prone conditions.There are few studies establishing the usability of this adhesive as a wood binder.Therefore,the main objective of this study is to develop various approaches for improving aluminophosphate wood adhesives,primarily through organic-inorganic materials hybridization.(1)In the first study,Polyvinyl Alcohol was used as the modifier.At the same time,glutaraldehyde was employed as a crosslinker to reduce the water uptake of aluminophosphate bond interface in Pinus massoniana plywood.The influence of the crosslinking on the reaction mechanism,morphology,thermal stability of the adhesives and tensile strength of the plywood was examined using FTIR,XRD,XPS,TGA,and SEM.The SEM images showed the absence of pores on the adhesive surface at 1,3 and 5 % glutaraldehyde.Apparently,crystalline peaks were observed in aluminophosphate adhesives at a lower reaction temperature(110°C).The C–O bonds were reduced,increasing C–C/C–H that could account for bond stability in water after revealing hydrogen bonding between the plywoodinterfaces.Consequently,the wet tensile strength of PVA/Aluminophosphate-based plywood was enhanced significantly(P < 0.05)above the type II Chinese standard,achieving strength as high as 1.02 MPa.Also,the dry tensile strength improved slightly to 2.34 MPa compared to unmodified aluminophosphate adhesive.Therefore,modification with PVA and the addition of glutaraldehyde as a crosslinker could enhance the water stability of aluminophosphate-based plywood.(2)Secondly,carboxymethyl cellulose was functionalized using 3-aminopropyl triethoxysilane to alter the chemical structures of the aluminophosphate adhesive.A face-centred central composite design based on response surface methodology was employed to generate the optimum production conditions for the improved plywood interfaces.Adhesive concentration and hot-press temperature were seen as the significant factors within tested limits.The most appropriate production variables were suggested with a valid predictive model for such conditions.Also,the reaction mechanisms revealed the successful altering of the aluminophosphate properties with a well-uniform adhesive surface.The results indicate that modified adhesives are more thermally stable.Furthermore,the wet bonding strength of the modified adhesive was improved above the minimum threshold(Chinese type II standard ≥ 0.70 MPa).Therefore,the sustainable(i.e.continuous availability of CMC)approach adopted in this research could be considered a viable method for improving the properties of aluminophosphate adhesives.(3)The third study produced mildew resistance and environmentally friendly adhesives to replace formaldehyde-based adhesives.This was achieved by incorporating nano-cupric oxide with functionalized carboxymethyl cellulose aluminophosphate adhesive.The effect of various amounts of nano-cupric oxide(1,1.5 and 2%)on the mildew resistance of the adhesives was tested.Also,the mechanical properties and adhesive chemistry were examined.The zone of inhibition of the Aspergillus niger V.Tiegh and Penicillam citrinum Thom cultured plates showed robust mildew resistance between the control and nano-Cu O treated adhesives and the coated bamboo fibre.Furthermore,the mildew control effectiveness also shows the nano-Cu O treated adhesive is more mildew resistant.Although,the mildew resistance slightly increased from 1 to 2% of nano-Cu O addition.The mechanical property of the plywood fabricated with the adhesive fulfilled the requirement for type II plywood.(4)Lastly,the structure of formaldehyde-free aluminophosphate adhesive was further altered to improve its water resistance.This was achieved through specialized procedures requiring the modifier(chitosan)activation using cheap,commercially available polymethylhydrosiloxane.Subsequently,three-layer plywood was fabricated at 5,10,and 15% concentrations of surface activated chitosan.The properties of the modified adhesives and also the plywood were examined using FTIR,XRD,XPS,TGA,SEM-EDS,and UTM.New functional groups were introduced into the aluminophosphate structural network.Clear and less porous microscopic surfaces were observed.The wet bonding strength at 15% concentration of surface activated chitosan met the type II plywood standard requirement.In addition,improved aluminophosphate adhesive shows superior economic benefits(in the estimated price index)than previous related findings.