Abstract: During experiments, it was found that urea has a good modifying effect on polyvinyl alcohol (PVA) glyoxal resin. Following the modification method of thiourea crosslinking PVA, a composite modified PVA polymer was prepared by solution polymerization through the modification effect of urea on PVA.
Keywords: Polyvinyl alcohol, Modification, Modifier
1 Experiment
1.1 Raw Materials and Instruments
Raw materials: Polyvinyl alcohol; Glyoxal, 40%, analytical grade, Sinopharm Chemical Reagent Co., Ltd.; Hydrochloric acid, 98%, analytical grade, Shanghai Reagent Factory No. 4; Sodium hydroxide, analytical grade, Jiangsu Qiangsheng Functional Chemical Co., Ltd.; Urea, analytical grade, Shanghai Lingfeng Chemical Reagent Co., Ltd.; Acetone, analytical grade, Jiangsu Qiangsheng Functional Chemical Co., Ltd.
Instruments: HH-2 digital display constant temperature water bath, Guohua Electric Co., Ltd.; JJ-1 precision booster electric stirrer, Guohua Electric Co., Ltd.; METTLER TOLEDO EL204 electronic balance, Mettler Dolittle Instruments (Shanghai) Co., Ltd.; NICOLET 380 Fourier transform infrared spectrometer, Thermo Scientific, USA; potassium bromide tablets.
1.2 Experiments
1.2.1 Synthesis Principle of Modified Polyvinyl Alcohol
The synthesis of polyvinyl alcohol glyoxal resin utilizes the cross-linking polymerization of the hydroxyl groups in the PVA molecule with the two carbonyl groups in the glyoxal molecule under acidic catalytic conditions. In practice, the cross-linking reaction between molecular chains occurs within a very short structural unit within the polyvinyl alcohol molecule.
Modified polyvinyl alcohol polymers are obtained by forming an acetal structure under acidic conditions and by modifying specific groups of the acetal polymer with urea.
1.2.2 Experimental Design
The experiment was conducted based on a ratio of mₚᵥₐ:m water:m glyoxal = 15:150:6, with a constant amount of polyvinyl alcohol used. Glyoxal was selected as the main modifier, and urea was used as a modifier to modify the polyvinyl alcohol glyoxal resin matrix, obtaining a composite modified polyvinyl alcohol polymer.
1.2.3 Preparation Process
Polyvinyl alcohol and water were added to a four-necked flask equipped with a stirrer, thermometer, and dropping funnel, and kept at 95℃ for 1 hour to ensure complete dissolution. Hydrochloric acid was added dropwise to adjust the pH to 1.5. The temperature was lowered to approximately 80-85℃, and the prescribed amount of glyoxal was slowly added dropwise over 30 minutes. The mixture was kept at this temperature for 1 hour, and sodium hydroxide solution was added to adjust the pH to 7-8 (neutral). The temperature was then lowered to 65-70℃, and after stabilization, a certain amount of urea was added. The reaction was then maintained at 65-70℃ for 1 hour.
2. Experimental Results The absorption peaks at 1159.69 cm⁻¹ and 1454.56 cm⁻¹ in the figure are characteristic peaks of polyvinyl alcohol glyoxal resin. Through modification of polyvinyl alcohol, the characteristic peak at 1640.85 cm⁻¹ split into two characteristic peaks at 1625.41 cm⁻¹ and 1669.91 cm⁻¹. This indicates that a novel composite modified polyvinyl alcohol polymer was obtained through solution polymerization.
3 Conclusions Through the study of glyoxal and urea composite modified polyvinyl alcohol, it was determined that glyoxal/urea composite modified polyvinyl alcohol polymers can be prepared by solution polymerization under certain conditions. References [1] Sun Youhong. Preparation of water-soluble polyvinyl alcohol glyoxal adhesive [J]. Journal of Nanjing Xiaozhuang University, 2009, 23 (3): 42-44. [2] Zhang Changhua, Zheng Xiang, Chen Gao, Ge Wenxi. Synthesis process of polyvinyl alcohol-glyoxal acetal resin (Anhui University of Technology SRTP Project, 08026) [J]. Shanghai Chemical Industry, 2008, 33 (12): 16-18. [3] Zheng Youming, Hu Xiaoyong, Chen Yao. Preparation and application of glyoxal-modified polyvinyl alcohol protective colloid [J]. China Adhesives, 2012, 21 (10): 22-25, 42.
[4] Zhang Changhua, Gu Xupeng, Qiao Hongbin. A method for preparing thiourea crosslinked polyvinyl alcohol glyoxal adhesive, China, 201110079419.7 [P]. Anhui University of Technology, 2011.10.12.
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