低甲醛脲醛树脂的合成工艺及其结构性能研究

【作者】 朱利平；

【导师】 顾丽莉；

【作者基本信息】 昆明理工大学 ， 应用化学， 2003， 硕士

【摘要】 作为木材工业上的主要胶种，脲醛树脂除了有成本低、原料易得、粘接强度高等优点外，也存在一些严重的不足，诸如耐水性差、胶层脆性大、易老化、贮存期短，特别是游离甲醛含量高。这些都严重地影响脲醛树脂胶的应用范围及制品质量的提高。因此，明确脲醛树脂树脂结构与性能的关系，探索一种降低脲醛树脂中游离甲醛含量，全面提高树脂综合性能的技术途径具有重要的理论与实践意义。 本文综述了国内外脲醛树脂的生产和使用现状，全面分析了脲醛树脂的研究进展和国内外研究动态。针对脲醛树脂胶粘剂存在的问题，在大量实验的基础上对脲醛树脂的合成工艺以及结构与性能的关系进行了全面的研究。主体内容分为四个部分： (一)．脲醛树脂合成工艺优化分析。首先，对脲醛树脂生产上主要的两条合成工艺路线进行了对比研究，结果表明：传统的弱碱—弱酸—弱碱合成工艺生产的树脂具有贮存稳定性好、胶接强度高、易操作等优点，但游离甲醛含量难以控制，而强酸条件下的中低温合成工艺合成的树脂具有较低的游离甲醛含量，但羟甲基含量过低，树脂胶接强度不佳，且生产中操作控制难度大。其次，研究了主要合成工艺参数对脲醛树脂性能的影响，结果表明：①．随着甲醛与尿素摩尔比(F／U)的降低，合成产物的粘度和固含量升高，游离甲醛含量降低，树脂的固化时间延长；②．反应体系的PH值，特别是缩聚阶段的PH值对树脂的性能影响很大，PH值愈低，树脂中游离甲醛含量愈高，粘度增大。缩聚阶段适宜的PH值范围为4～6；③．反应温度的提高可加快合成反应速率，在一定温度下，反应体系的粘度和固含量随反应时间的延长而上升，最后达到一稳定值。 (二)．低甲醛脲醛树脂的合成及改性。在这一部分，实验研究了脲醛树脂中游离甲醛含量与原料摩尔比的关系，确定了甲醛与尿素的最佳摩尔比为1.2：1。酸性反应阶段摩尔比对脲醛树脂的胶接性能和贮存稳定性有很大的影响，平衡两者的关系须控制酸性反应阶段摩尔比在2.0：1～1.6：1之间。在此低摩尔比的配方下添加适量PVA、苯酚作为改性剂，树脂中游离醛含量稳定地降到了0.15％以下。PVA最佳加入量为昆明理工人学硕士学位论文摘要体系总重的0.5一1.0%，苯酚最佳加入量为体系总重的0.5%。改性剂的低加入量使在几乎不增加树脂成本的情况下，大大改善了树脂的综合性育旨。 (三).脉醛树脂结构与性能的关系。通过对脉醛树脂合成反应体系中不同反应阶段样品的FT IR谱分析，定性地研究了随着合成反应的进行，不同基团含量的变化情况。利用常规化学分析方法分析了脉醛树脂样品的宏观性能参数，同时用‘;℃NMR谱分析各样品，研究了服醛树脂胶微观结构与宏观性能的关系，并可通过观测某些微观结构如一NHCHZNH一基团的吸收强度来控制合成脉醛树脂的反应程度。 (四).脉醛树脂合成反应初期动力学研究。对在碱性条件下，脉醛树脂反应初期甲醛与尿素的反应机理和动力学进行了讨论，并创造性地提出了可能的二级不可逆加成反应速率模型，其速率方程为一~In~一、"。一方;‘。通j、实。、定。!，也。、析了初始摩尔。匕、体系(n:一l)e月;，c刁.，一nlyI’11值矛!!反应温度对加成反应速率的彩响，结果表明:F/U值越大，反应温度越高，反应速率越快。更多还原

【Abstract】 As a main adhesive used in wood industry, Urea formaldehyde resin ( UF resin) has many advantages such as low cost, available raw materials, excellent agglutinative intension and so on. However, it has some disadvantages: poor water-fast quality, brittle layer, quickly ageing, short shelf-time, especially high content of free formaldehyde which seriously hinders UF resin using range and its product quality. Therefore, it is of great academic and applied significance for us to determine the relationship between structure and quality of UF resin, seek a technique way to decrease the content of free formaldehyde in UF resin and to improve roundly the resin’s quality.In the beginning of this paper, the actual state of industrial production and usage of UF resin were introduced respectively, then the study progress and situation of UF resin in domestic and abroad. In order to resolve problems mentioned above, the synthetic technique of UF resin and the relationship of the resin structure and its quality were generally researched on the basis of a large quantity of experiments. The experiments were done from the four main parts as follow:1.The study of optimum synthetic technique of UF resin. First, the results of the comparative study between two common technique routines show: the traditional synthetic technique of weak basic - weak acidic -weak basic has some advantages of good stability, excellent agglutinative intension and simple operation etc., but it is difficult to control the content of free formaldehyde in the resin. The products of the middle-low temperature technique based on strong acidity can provide with the quality of low content of free formaldehyde, but the shortcomings of the technique are too low content of methylic hydroxide, bad agglutinative intension and difficult operation in procedure. Secondly, the study results of the relation between main technical parameters and the quality of UF resin show: (1).With the decreasing of the mole-ratio of formaldehyde and urea(F/U) , the viscosity and solid-content increase, but the content of free formaldehyde decreases and the solidifying-time of products prolongs; (2) .The PH of reactive system, especially the PH in the phase of polycondensation works greatly on the quality of UF resin. The smaller the PH is, the higher the content of free formaldehyde and the viscosity of resin are. The fitting PH range in the phase of polycondensation is from 4 to 6; (3). The increase of reactive temperature could accelerate the synthetic reaction. At a suitable temperature, the viscosity and solid-content increase with the reactive time until they reach a stated value.2. The synthesis and modifying of UF resin with low-content of free formaldehyde. In this part, the relationship between the content of free formaldehyde and the mole-ratio of raw materials was determined with the experiments. The optimum mole-ratio occurs at 1.2 : 1. The mole-ratio in the phase of acidic reaction has a great influence on the agglutinative intension and stability of UF resin and it should be kept in the range of 2.0 ; 1 ~ 1.6 : 1. The low mole-ratio formulation was applied to the preparation of urea-formaldehyde resin in which an appropriate quantity of polyvinyl alcohol, phenol were used as modifiers. The results showed the free formaldehyde content in the products was steadily lower than 0.15%. The best quantity of PVA and phenol were respectively 0.5~~ 1.0% and 0.5% of the total weight of reactants. The small quantity of modifiers almost don’t increase the cost of resin, but all-round properties of UF resin were remarkably improved.3. The relation of structure and quality of UF resin. Through the FTIR analysis of resin sample in different stage of a synthetic reaction, we qualitatively discuss the change of different radical content in the course of synthetic reaction. The ordinary chemical analysis and 13CNMR were employed in order to research primarily the relation of microstructure and macroscopical quality of UF resin. The results of study illuminate that the reactive pro更多还原