Study On Influence Of Polyurethane On Properties Of Isocyanate Bonding System

With the rapid development of wood-based panel industry,in recent years,China has become the world's largest wood-based panel production and consumption market.At present,the main adhesives for wood-based panels in China are urea-formaldehyde resin,phenolic resin,and melamine-formaldehyde resin,which account for more than 90% of the adhesives for wood-based panels industry.With the improvement of people's quality of life and the enhancement of environmental awareness,formaldehyde problem has attracted more and more attention.The production of environmentally friendly wood-based panels with low or no formaldehyde has become the future development direction of the industry.The key part is the research and development of low or no formaldehyde adhesives.Isocyanate is one of the most commonly used formaldehyde-free adhesives.It has the advantages of high bonding strength,good waterproof property,fast curing speed and no formaldehyde release from bonded wood-based panels.However,the monomer component in isocyanate is easy to penetrate into wood pores resulting in the lack of glue on the veneer surface.Therefore,isocyanate is generally not directly used for bonding plywood.Polyurethane is one of the most widely used macromolecule materials,which also produces a lot of waste each year.Because polyurethane is not easy to degrade,a large number of stacking will bring a great burden to the environment.Therefore,the recycling of waste polyurethane has become an urgent problem to be solved.In this study,the theory and practice of the application of waste polyurethane materials in isocyanate-bonded wood composite panels were discussed.First,polyurethane foam was collected and processed,and polyurethane powder with different particle sizes(60 mesh,120 mesh,and 180 mesh)was prepared and added to isocyanate at different ratios(2.5%,5%,7.5% and 10%)to form a series of isocyanate bonding systems.The effect of polyurethane addition on the properties of the bonding system was studied.Infrared spectroscopy was used to characterize the structure of the system.Thermogravimetric analysis and differential thermal analysis were used to study the thermal stability and curing reaction of isocyanate bonding systems.The bonding strength was investigated through the preparation and test of the plywood.The conclusions are as follows:(1)After adding a certain amount of polyurethane powder to the isocyanate,the viscosityof the bongding system increased,which could effectively prevent the veneer surface from penetration and improve the bonding strength of the plywood.(2)The consumption of isocyanate group during curing increased with the increase of polyurethane content,and the reaction between isocyanate group and polyurethane occured.This reaction is conducive to promoting the curing of isocyanate and improving the performance of cured resin.(3)Compared with pure isocyanate resin,the thermal weight loss of the isocyanate system increased slightly,but the thermal weight loss between the systems had little difference due to the low amount of polyurethane added.(4)Compared with pure isocyanate resin,the initial curing temperatures of isocyanate systems decreased.The peak curing temperature decreased,the peak heat flux of curing reaction increased,and the curing reaction efficiency generally increased.(5)The bonding strength of plywood bonded with isocyanate systems increased with the decrease of particle size of polyurethane powders,and the bonding strength of plywood decreased with the increase of particle size of polyurethane powders.In this experiment,the bonding strength of plywood bonded by resin systems with 120 mesh and 180 mesh polyurethane powder had the highest values.(6)When polyurethane powders with different amounts(2.5%,5%,7.5%,and 10%)were added to isocyanate,the mechanical properties of plywood increased with the increase of the amount of polyurethane powders.In this experiment,the boiling water bonding strength of plywood bonded by resin systems with 7.5% and 10% polyurethane powders had the highest values.In conclusion,the isocyanate bonding systems formed by adding polyurethane powders had certain practical application value.The plywood bonded by these systems could fully meet the requirements of GB/T 9846-2015 for class I type.Considering the processing economic and resin application convenience,the bonding performance of the system could get best results when the polyurethane mesh was between 120 and 180,and the proportion was between 7.5% and 10%.In this study,waste polyurethane materials were applied to wood-based panels production practice,which could not only reduce the cost of adhesives used in wood-based panels industry,and improve the performance of wood-based panels,but also save resources,reduce the impact of waste on the environment,and achieve the recycling of resources.