Study On Reaction Outcome Of Isocyanate With Wood Components

In the past two decades, because of non-formaldehyde, short-time curing and high-bonding strength, isocyanate resins have been become an important adhesive in woodprocessing industry, which are used in jointing plate alignment, furniture manufacture andprocessing non-wood based panels, such as wheat straw panels. People increasingenvironmental consciousness and wood material decreasing, isocyanate adhesives will play aimportant role in the wood industry.The reactions that isocyanate reacted to cellulose, lignin, semicellulose and water intimber to form the urethane and urea under certain conditions are basic reactions ofisocyanate resins and timber, they have significant meaning to understand that differentquantity of urethane and urea affect the strength of adhesive bond.The paper regarded phenyl isocyanate(PI) as model, the first step: the paper mainlystudied on thc rcactions between the PI and lignin, cellulose, wood powder by the differentialscanning calorimetry (DSC) technique. In different calefactive rates, it characterized thereactions of PI with lignin, wood powder, respectively, with two moisture contents (MC) whichwere absolute dry moisture content (MC=0%) and equilibrium moisture content (MC=3%for lignin, and 5% for wood powder). It also evaluated the reactions characterizations of PIwith the mixtures of lignin and cellulose with different weight ratios; the second step: the PI,cellulose, lignin and wood powder were used in experiment in this paper to react underdifferent conditions (taking moisture content,time,temperature into account), then produceoutcome A(contain urethane and urea),then acetone was used to dissolve the urea from A, theoutcome B(contain urethane only) was attained, the nitrogen content of A and B was mensurateby Kjeldahl method. By this way the quantity of the urethane and the urea under the differentreaction condition was known.The results showed: based on the analyses to the DSC curves and Ozawa equation, theactivation energies of the reactions of the PI/lignin, PI/wood powder were obtained, by whichthe reaction characterizations of the PI with lignin, cellulose, and wood powder are discussed.The study indicated that the reaction temperature and activated energy of PI/lignin systemwere lower than those of PI/wood system. The PI mainly reacts with lignin when cellulose andlignin were mixed together. However, the reaction degree of PI with cellulose increased withthe cellulose content increasing in cellulose/lignin mixture. When the moisture content of woodreached 5%, the reaction activation of PI/wood system reduced 34%. When PI reacted with cellulose, the output of urea was much more than the output ofurethane under the different moisture content, time and temperature. When PI reacted withlignin, the output of urethane was much more than the output of urea under the differentmoisture content, time and temperature. The molecular quantity of urethane that from thereaction of PI and wood powder is between the quantity of reaction of PI and cellulose and thequantity of reaction of phenyl isocyanate and lignin, it is up to the organic construction of thewood.