| Although using the bivalent metal ionic hydroxide as a catalyst to regulate the curing temperature of phenolic resin was a common and feasible method,few research was done on its synthetic mechanism and its application in dyeing for wood and bamboo plywood.In order to solve the discoloration problem of dyed bamboo and wood plywood during the high temperature bonding process with the use of phenolic resin,this thesis provided a controllable technology to reduce the plywood color difference so as to improve the product quality.The phenolic resin,which was directionally synthesized could be rapidly cured at a low temperature.In this thesis,the catalytic effects of Zn2+,Mg2+,Ba2+ and Ca2+ hydroxides on the polymerization rate,solid content and viscosity of phenolic resin were studied.TG-DSC,FTIR and other analytical methods were used to further study the formation process and curing performance of phenolic resin with high ortho-molecular structure under the catalysis of different kinds of divalent metal hydroxide and addition amount.The synthesis process parameters of low temperature fast curing phenolic resin were optimized by orthogonal combination of F/P ratio,alkali catalysis dosage,reaction end point control etc..Meanwhile,the hot pressing process of modified phenolic resin plywood was further optimized by response surface analysis method.In addition,the high-ortho-synthesis mechanism of the modified resin and the kinetics of the curing reaction were calculated.The modified phenolic resin,used as the adhesive of the dyed recombinant bamboo panels,was applied and tested on the dyed bamboo-based panel to determine the modification.The preparation technology of phenolic resin and hot pressing process provided scientific guidance for the research on green manufacturing of wood-based panels for energy saving and consumption reduction.The main conclusions were as follows:(1)The effects of divalent metal ion hydroxide on the solid content of phenolic resin was Bat+>Mg2+>Ca2+>Zn2+,and the optimal addition amount was 0.8%,0.4%and 0.6%of phenol mass ratio,respectively.The effect of Zn2+ on increasing the solid content of phenolic resin was not obvious.As the amount of different divalent metal ions increased,the viscosity of the phenolic resin increased first and then decreased.The 4 kinds of divalent metal ions had a certain effect on increasing the polymerization rate of phenolic resin.Ba2+ had the best effect.When the addition amount was 0.3%of phenol mass,the curing time could be shortened by 24%,followed by adding 0.15%of Ca2+,0.05%Mg2+ and 0.4%Zn2+.(2)The FTIR curve showed that the initial reaction of the resin catalyzed by Ba2+,the characteristic peaks of the 757 cm-1 ortho-substitution and the 826 cm-1 para-position were substituted according to the standard spectrum,the intensity of the absorption peaks of the two wave numbers was very small,and the substitution number of the alignment and the ortho position were also small and essentially indistinguishable.At the end of the reaction,the absorption peaks at 757 cm-1 and 826 cm-1 began to differ,and the area of the peak at 757 cm-1 increased,indicating that the ortho substitution began to dominate.The reaction endpoint curve showed that the absorption peaks at 757 cm-1 and 826 cm-1 began to show significant differences,and the ortho-substitution was much higher than the para-position substitution.The curves of the Ca2+ and Mg2+ modified phenolic resins were the same,but this was not observed in the infrared spectrum of the blank samples.(3)The TGA curve showed that the Barsa modified phenolic resin began to reach a curing exotherm near 110?,while the initial curing temperature of Ca2+ and Mg2+catalytically modified phenolic resin and blank samples increased.The curing reaction proceeded further at 200? to 300?.The Ba2+ modified phenolic resin sample had the highest heat release rate,and the Ca2+,Mg+ modified phenolic resin sample and the blank sample had a lower heat release successively.It was indicated that the Ba2+modified phenolic resin sample near 110? had the best crosslinking curing degree,in another word,the Basa modified phenolic resin could be cured at a lower temperature.(4)The DTG curve showed that there was a significant weight loss peak around 120 ?.The main reason for the weight loss of the resin at 100?140 ? was the water volatilization.The weight loss ratio of this part was inversely proportional to the solid content.The DSC curve showed that the temperature of the maximum decomposition rate of the Basa modified phenolic resin sample emerged the earliest,indicating that the curing was the easiest.The temperature of the maximum decomposition of the resin modified by Ca2+ and Mg2+ were also earlier than that of the blank sample.The apparent activity of the curing reaction of the 3 divalent metal ion-modified phenolic resins was calculated,and the apparent activation energies of Ba2+,Ca2+ and Mg2+catalyzed phenolic resins were 87.4,87.1 and 111.1 kJ/mol,respectively.The curing reaction of Ba2+ and Ca2+ modifned resin was easier than that of Mg2+ modified one.The curing temperature of the 3 ion-modified phenolic resins was lower than that of the ordinary phenolic resin.(5)Orthogonal test design and gluing test were carried out on the factors of divalent metal ions,F/P ratio,base catalysis dosage and reaction end point control synthesis process.The effects of different process conditions on the bonding strength and other indicators were investigated.After the comprehensive balance,the optimal combination of synthesis process was F/P=2.3,NaOH/P=0.4,the type of divalent metal ion was Ca(OH)2,the addition amount 0.45%of phenol,and the reaction end viscosity 380 mPa.s.The optimal combination was tested and verified.The synthesized phenolic resin had good physical and chemical properties,the appearance was reddish brown,the viscosity 400 mPa.s(25?);the pH 10.9;the solid content 49.53%;the curing time 1963S;the pot life 220m;the free aldehyde 0.231%;and the shear strength of the pressed 3-layer poplar plywood 1.58MPa.After comparing the optimal combination of the two groups with the best combination,except for the deficiencies of resin's appearance and the bonding strength,other properties were basically same.(6)Curing time was tested after adding a certain amount of curing agent to the modified phenolic resin.The curing effect results was:propylene carbonate>sodium bicarbonate>anhydrous sodium carbonate>paraformaldehyde>resorcinol>ammonium chloride.The curing effect of propylene carbonate was the best,but it turned green after curing.Due to the short period of activity,sodium bicarbonate could hardly cure in a short time after adjusting,and it could not be applied either.Therefore,anhydrous sodium carbonate was selected as the curing agent for the study,and its dosage was 4%.(7)Based on Box-Benhnken's central combination test design principle and adopted the response surface method to optimize the hot pressing process of modified phenolic resin plywood,we finally got the best bonding process:resin applying amount 25g/side(i.e.277.8g/m2),the ratio of the curing agent 3.5%,the hot pressing temperature 108?,the hot pressing time 34.99 s/mm,and the predicted maximum response value 1.623 MPa.The optimum process was verified and the average shear strength of the sample was 1.64 MPa,which was comparable to the model prediction.(8)In view of the phenomenon of product discoloration during the production process of dyed recombinant bamboo panel,the hot pressing process such as adhesive,hot pressing pressure and hot pressing temperature were selected to investigate on the effect of dyeing treated poplar veneers on the color difference before and after gluing.The results showed that the color difference of the nine dyes was not significant,but the adhesive had a significant effect on the color difference of the nine dyes,and the temperature had a significant effect on the color difference of the five dyes.The interaction between temperature and dye significantly affected the color difference of the three dyes.At the same time,it was shown that the sensitivity of dyes of different color systems was also different.Compared with reactive blue dyes,acid blue was more responsive to temperature.Yellow dyes were more sensitive to temperature than red ones because the red dye structure was more stable than the yellow one.(9)Bamboo strips were first dyed with acid dye.Then we tested and compared the color difference and physical and chemical properties of recombinant bamboo panel with Ca2+ modified phenolic resin and ordinary one.The results of color difference test showed that low temperature curing could reduce the color difference of dyeing and improve the color retention effect of dyed recombinant bamboo panel.The effect of acid red dye was the most obvious.The mechanical properties of the recombinant bamboo had a static bending strength of 136.8 MPa and an elastic modulus of 14012 MPa.The static bending strength and elastic modulus of the recombinant bamboo of the general phenolic resin were basically the same,indicating that the Ca2+ modified phenolic resin could be fully cured by the dyed recombinant bamboo panels.The release amount reached the E1 standard.Finally,the energy consumption of the two hot pressing processes was calculated.The results showed that the low temperature modified phenolic resin process saved 33.31%energy compared with the ordinary phenolic resin process.This thesis systematically studied the bivalent metal ion hydroxide catalyzed modified phenolic resin and its application,clarified its catalytic mechanism,studied and optimized the synthesis process and hot-pressing process,and provided basic data and certain theoretical guidance for the application of low-temperature fast curing phenolic resin in dyed bamboo and wood panels. |
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