Preparation of Plywood Using Starch Adhesives Modified with. Isocyanate

Transcription

1 Applied Mechanics and Materials Vols (2010) pp Online available since 2010/Jun/30 at (2010) Trans Tech Publications, Switzerland doi: / Preparation of Plywood Using Starch Adhesives Modified with Isocyanate Jiyou Gu a, Yingfeng Zuo b, Yanhua Zhang c, Hanyan Tan d, Libin Zhu e, Jun Shen f College of Material Science and Engineering, Northeast Forestry University, Harbin, China, ,P. R. China a dldgujy@163.com, b zuoyf1986@yahoo.com.cn, c zyhnefu@163.com, d tanzzx168@163.com, e zhulb600@vip.sina.com, f shenjunr@126.com Key words:isocyanate; Starch Adhesive; Plywood; XPS Abstract:The purpose of the study was to manufacture plywood using starch adhesives modified by isocyanate, the influence factors on the bonding strength and water resistance of starch adhesive were studied by different solid content, adding additives and adding isocyanate. X-ray photoelectron spectroscopy (XPS) analysis was used to characterize the chemical structure of bonding interface. The results show that the bonding strength of starch adhesive was increased significantly when solid content increased to 50%. Bonding strength and water resistance were improved significantly by adding additives and isocyanates to starch adhesive. The analysis of XPS indicated that the chemical bonding derived from the reactions of isocyanate was the key factor to increase bonding strength and water resistance. Introduction With the characteristics of abundant raw materials, simple process, convenient operation, low cost, well adhesion and film forming, non-formaldehyde emission, as well as the bright spot of environmental protection and renewablity, starch adhesive is the most potential one for development in the range of wood adhesives. But due to the performance of poor water resistance, poor storage stability and the low bonding strength, the starch adhesive was limited to application only in timber industry. Thanks to the characteristics of excellent bonding properties, water resistance, anti-aging, none formaldehyde and other pollution, isocyanate adhesive is adapt to a wide range of adhesive materials, and help to improve the quality of adhesive products and wood utilization. With the increasing requirements of environmental protection and people's environmental awareness, efficient development and application of pollution-free synthetic resin wood adhesives have become the issues of common concern, but moisture-curing isocyanates adhesive complies with the requirements of the times because of non-formaldehyde. Aimed at the characteristics and disadvantages of starch adhesive as well as the advantages of isocyanate adhesive, using isocyanate modified starch adhesive by added a small amount of isocyanate was studied in this paper, and improving the plywood bonding strength and water resistance in order to expand the application scope of starch adhesive was expected. Experimental Materials and Methods Materials. The starch adhesive was synthesized by our laboratory, the solid content of adhesive using in the experiment were 30%, 40% and 50%; Viscosity was mPa.s measured by rotational viscometer at 23 ; Polymeric methane dipthenyl diisocyanate (pmdi) which contains 29.5% of -NCO with an average functionality of 2.7was supplied by Bayer Polymer Ltd. Co (branch company, China). Urea-formaldehyde resin was used as additives in the experiment. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, (ID: , Pennsylvania State University, University Park, United States of America-15/06/14,02:44:02)

2 1066 Advanced Mechanical Engineering Test Instruments and Test Equipment. Pre-press and hot-press machines, universal mechanical testing machine, oven, rapid moisture meter, electronic scales, calipers, constant temperature water bath and so on. Parameters of Plywood Manufacturing mm of poplar veneer and 8~10% of moisture content, 320g/m 2 of coating amount, 2Mpa of preloading pressure, 3MPa of hot pressure, lmin/mm of hot-press time and 120 of hot-press temperature. X-ray Photoelectron Spectroscopy (XPS).XPS measurements were performed at room temperature with monochromatic AlKα radiation (1486.6eV) using a K-Alpha X-ray photoelectron spectrometer (supplied by Thermo Fisher Scientific Co., Ltd). The X-ray beam was a 100-W, 200mm-diameter beam raster over a 2mm by 0.4 mm area on the sample. High-energy photoemission spectra were collected using pass energy of 50eV and resolution of 0.1eV. For the Ag3d5/2 line, these conditions produced an FWHM of 0.80eV. Results and Discussion Effect of Different Solid Content on the Bonding Strength. Experiments were used starch adhesive pressed plywood with solid content of 30%, 40% and 50% in order to study solid content of starch adhesive effect on the bonding strength. The bonding strength of the plywood was tested, and the results were shown in Table 1. When the solid content was increased from 30% to 40%, the dry strength of plywood pressed with starch adhesive was only slightly changes;but while solid content was increased to 50%, the bonding strength was increased significantly. Since poor water resistance of starch adhesives, wet strength was zero. When Solid content at 30%, 40% and 50%, the wood specimen failure rate were 0, 20 % and 100%, respectively. Therefore, the bonding strength corresponding increased along with the increased of solid content, and the solid content of the starch adhesive at 50% could achieved well bonding strength. Table 1. the bonding strength of starch adhesive with different solid content Solid content 30% 40% 50% Dry Strength (MPa) Wet Strength (Mpa) Effect of Isocyanate and Additives on the Bonding Strength. In order to study the effect of additives and isocyanates on the bonding strength of starch adhesive, a total of 3 groups comparative experiments were carried out. Pure starch adhesive, starch adhesive with additives and starch adhesive with additives and isocyanates were used to pressed plywood. The bonding strength of the plywood pressed in these three methods was tested, the results were shown in Figure 1. The wet strength of the plywood pressed with pure starch adhesive was zero, while adding a small amount of additives, the dry strength decreases slightly, but the wet strength was improved to some extent. When adding small amounts of isocyanate, the wet strength was improved significantly, which indicated: adding additives could be appropriate to improve the water resistance of starch adhesives. While adding the small amount of isocyanates could improve the bonding strength and water resistance of starch adhesive better.

3 Applied Mechanics and Materials Vols dry Strength wet Strength bonding strength(mpa) A B C Figure 1.Effect of Isocyanate and additives on the bonding strength (A.pure starch adhesive, B. A with additives, C. A with additives and isocyanate) XPS Analyze the Chemical Structure of Bonding Interface. The interface chemical structures of plywood with bonding joint with the optimum ratio were analyzed, the results shown in Figure 2 and Table x x x x x x x x x10 4 6x10 4 5x10 4 O1s N1s C1s O1s B 5x10 4 4x10 4 3x10 4 2x10 4 1x x x10 3 C1s C C1s D C1s B C1s A N1s A 4x10 4 3x10 4 2x10 4 1x x10 3 O1s A4.5x x10 3 N1s B 0 3.5x Figure 2. adhesive interface XPS spectra of adding additives and isocyanate It is can be seen clear in Figure 2 and Table 2 that the chemical structure of adhesive layer contains a certain amount of the bonding of carbon and nitrogen with the content of 1.27% which is form isocyanate, it was fully confirms that isocyanate adhesive reacts with hydroxyl of starch and wood. High-resolution spectra of the nitrogen can also be seen isocyanate reacts with water vapor generated substituted urea, but also reacts with hydroxyl of starch adhesive and wood which had generated carbamate. Therefore, the interface layer analysis further confirmed the skeleton status of isocyanates was essential crosslinker of starch adhesive in preparation of plywood.

4 1068 Advanced Mechanical Engineering Table2. percentage content of elements in the bonging interface Name Peak BE(eV) group At % C1s A C-C C1s B C-N/-C-O C1s C O-C-O C1s D N-C=O 1.34 N1s A C-N N1s B O=C-N-benzyl 0.32 O1s A N-C=O 8.23 O1s B O-C-O Conclusions Preparation of plywood with the different solid content of starch adhesive, the results show that the bonding strength was greatly improved when the solid content at 50%; adding a small amount of additives into the starch adhesive, bonding strength and water resistance experience a certain improvement; however, while adding isocyanate, bonding strength and water resistance are significantly improved. Used XPS analysis the bonding interface, the chemical bonding from by isocyanate adhesive reacts with the hydroxyl of wood and starch was the key to increase bonding strength and water resistance. This paper illustrates that isocyanate play a good role in improving the bonding strength and water resistance of starch adhesive. Acknowledgements The author gratefully to acknowledge the financial support of National Nature Science Foundation of P R China (grant No ) and the support of the project of Harbin (grant No. 2008AA4BG006). Special thanks to outstanding doctoral dissertation foster support for the study and the support of project of NEFU (grant No.09013). Special Scientific Research Project of Public Welfare for Environmental Protection( ). References [1] L.H.Li, G.J.Liu, G.X.Zhang, The Latest Progress in Study on Starch-based Adhesives. Chemistry and Adhesive, Vol. 30. No. 5(2008), p [2] Y.H.Liu, R.S.Ruan, J.S.Zhang, Research Situation of Starch Based Wood Adhesives. Chemistry and Adhesive, Vol. 27.No. 6, (2005), p [3]Y.H. Zhang, J.Y.Gu, H.Y.Tan, Preparation of the Plywood Using UF Resin Modified with Blocked Isocyanates as Bonding Agent. China Forest Products Industy, Vol. 36.No. 6(2009), p [4] Y.B.Huang, Q.Y.Huo, The Application of Isocyanates Adhesive in Timber Industry, Journal of HeiLongJiang Ecological Engineering Vocational College, No. 6,(2006), p. 34~35.

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