【作者】 张彦华；

【导师】 顾继友；

【作者基本信息】 东北林业大学 ， 生物材料工程， 2011， 博士

【摘要】 脲醛树脂胶粘剂由于其制造工艺简单,原料廉价易得,初始粘度大,粘接强度较高,无色透明等优点。但脲醛树脂胶粘剂存在这耐水性差、固化物脆性大、耐老化性能差、游离甲醛含量过高等一系列问题,一直未得到有效解决,严重影响了脲醛树脂胶粘剂的主导地位。非甲醛系异氰酸酯胶粘剂具有胶接性能优良、较好耐水性、较好耐老化、无甲醛污染等优点、对被胶接材料适应范围广,同时异氰酸酯也具有活泼性大、胶接效果好、胶接工艺性较好。作为木材胶粘剂使用的封闭异氰酸酯要求其解封闭温度低于100℃,且封闭效力高,常温保存稳定性好,对于乳化异氰酸酯具有工艺简单,改性成本低廉而具有较好的应用基础。论文系统介绍了异氰酸酯的用途和作用机理,针对它在实际应用方面存在的缺陷,阐明了对它进行封闭和乳化的必要性；并且将改性异氰酸酯与脲醛树脂进行复合,系统研究了改性异氰酸酯与脲醛树脂复合固化机理反应。具体研究内容如下：(1)本文系统地研究搅拌速度对封闭异氰酸酯产物的影响,采用促进剂和稳定剂对封闭异氰酸酯乳液进行稳定性研究,以产物封闭率、pH、黏度、产物解封闭性能为评价指标。通过粒径、DSC、TGA、以及FTIR方法进行分析测试。FTIR结果表明,在封闭反应中,异氰酸酯特征官能团-N=C=O会随着封闭反应的进行而消失；在解封闭反应研究中,异氰酸酯完全被封闭,红外研究结果还表明解封闭温度范围60-100℃,60℃开始解封闭,当解封闭温度达到70℃后,解封闭速度也越快。DSC结果表明,在50-100℃温度区间有吸热现象,证明封闭异氰酸酯乳液发生解封闭反应,其中最佳条件的封闭产物吸收峰值明显而尖锐,解封闭反应较快,且随着恒温温度的升高,解封闭速度越快,其解封闭反应的时间约为10min。热重分析结果表明,采用不同比例促进剂、稳定剂以及不同处理方法制备封闭异氰酸酯有明显不同的热稳定性能差异。NaHSO3/NCO摩尔比为1.2的配比最为适合。促进剂加入摩尔比例为0.2mol,稳定剂为0.5%的条件下,制备的封闭异氰酸酯乳液粒径最小,分散最均匀。用不同溶剂对封闭异氰酸酯乳液进行洗涤处理以及进行冷冻干燥处理,分别采用DSC、TGA、FTIR和XPS以及定量方法对其产物进行表征。实验结果进一步证实,亚硫酸氢钠能够完全封闭异氰酸酯,N,N-二甲基甲酰胺(DMF)可以促进封闭异氰酸酯的解封闭反应速度,化学测试测得的封闭率要偏高,实验封闭率在86.18%以上。本研究制备亚硫酸氢钠封闭异氰酸酯产物可在50-90之间进行解封闭效果较好。(2)采用不同条件和合成工艺制备乳化异氰酸酯,通过对其乳化现象、粘度、异氰酸酯基含量等乳液性能指标,研究了稳定剂浓度,摩尔比、乳化剂浓度等影响因素对乳液稳定性能的影响。结果表明,异氰酸酯基与羟基的摩尔比为50：1、稳定剂浓度为0.9%、乳化剂浓度为2%条件下制备异氰酸酯乳液的2小时异氰酸酯基含量、粘度和活性期较稳定。采用粒径对异氰酸酯乳液的粒径进行系统分析研究,结果表明：预聚体的粘度、摩尔比以及异氰酸酯基含量与其外观和粒径分布有直接影响,粒径越小,表明乳化异氰酸酯稳定性越高,因此选择摩尔比50：1为宜。乳化剂和稳定剂浓度的粒径测试图形趋势和粘度、适用期的趋势相同。(3)采用封闭异氰酸酯改性UF胶黏剂的热稳定性和固化反应规律研究,得到下列结论：在最佳条件下,以合成方式制备封闭异氰酸酯(BPI)对UF树脂胶黏剂的固化速度起促进作用,BPI对UF胶的固化过程起到比氯化铵更强的催化作用。以NaHSO3与p-MDI先复合加入UF树脂胶黏剂中,此种方法复合适用期较长,但对UF胶黏剂的固化比前者弱。DSC测试结果,以NaHSO3与p-MDI先复合加入UF中对复合胶黏剂的固化速度以及固化温度起的促进作用比BPI效果弱一些。TGA测试结果表明,封闭异氰酸酯加入能够提高复合胶黏剂的热稳定性能,但加入比例要适中,不能高于5/5,在2/8最好。通过FTIR分析,结果表明BPI与UF复合胶黏剂复合与NaHSO3与p-MDI混合加入UF树脂中的复合胶黏剂固化产物中含有新的化学键,分别是氨基甲酸酯-氨基键,氨基甲酸酯-亚甲基键,封闭异氰酸酯加入比例不同,生成的氨基甲酸酯键和取代脲吸收峰强度不同。通过XPS分析表明,BPI与UF制备的复合胶粘剂,NaHSO3与p-MDI混合加入UF树脂制备的复合胶粘剂,固化产物中都含有反应基团-N-C=O-C和-N-C=0-N。BPI与UF复合胶黏剂的-N-C＝O-N官能团相对含量大于-N-C=O-C官能团,说明BPI中的异氰酸酯与UF中的氨基反应占优势。NaHSO3与p-MDI混合加入UF的复合胶黏剂,固化产物中的-N-C=O-C相对含量大于-N-C=O-N,说明复合胶黏剂体系的异氰酸酯与UF中的羟基反应生成氨基键占优势。(4)同时,研究了乳化异氰酸酯改性脲醛树脂胶黏剂的热反应规律研究,通过对比实验,可以得出乳化异氰酸酯与脲醛树脂的复合比例,固化剂的酸性强弱对复合胶黏剂固化反应速率和热稳定性的影响。结果表明,乳化异氰酸酯加入可以促进脲醛树脂的固化反应速度,提高复合胶黏剂的热稳定性,但随着乳化异氰酸酯比例加大,热稳定性有下降趋势。固化剂的酸性对异氰酸酯改性脲醛树脂具有一定影响。当固化剂酸性越强,混合胶的适用期越短,而固化剂的催化效果较弱时,不能够满足实际生产需要,因此固化剂选择氯化铵与甲酸混合(pH为1)。通过FTIR和XPS测试分析,结果表明,EPU与UF混合反应发生反应生成氨基甲酸酯-氨基键,氨基甲酸酯-取代脲键；采用XPS方法可以对异氰酸酯改性脲醛树脂的固化结构进行较好表征,并由此可以定量得出异氰酸酯与脲醛树脂固化产物的化学结构。更多还原

【Abstract】 Urea formaldehyde adhesive was widely used with the advantages such as low cost, high viscosity, high bonding strength and light color. However, the utilization of urea formaldehyde adhesive is always constrained due to low water resistance, evident frangibility, poor aging property and high deviated formaldehyde content. Isocyanate adhesive included in non-formaldehyde class is of well bonding property, water resistance and aging-resistant performance. Meanwhile, isocyanate possesses the advantages such as great reactivity and fine manufacturability. Used as wood adhesive, blocked isocyanate was required to be of low deblocking temperature (lower than100℃), high blocking efficiency and well stability under ambient situation.In this paper, the utilization and reaction mechanism of isocyanate was introduced and the necessity for blocking and emulsion of isocyanate was explained according to the drawbacks in practical application. Then the modified isocyanate was blended with urea-formaldehyde resin, and the curing mechanism of this mixture was studied systematically. The research was shown in detail as follows.(1) The effect of stir speed on blocked isocyanate was studied according to the determinations of blocking ratio, pH, viscosity and deblocking performance. The LPS, DSC, TGA as well as FTIR were employed to conduct the analysis of the blocking resultant. The FTIR results showed that blocked isocyanate could be deblocked within the temperature ranging from60to100℃and the deblocking reaction got faster from70℃on. DSC results indicated that the phenomenon of heat absorption was aroused within the temperature from50to100℃, which could testified that the deblocking reaction definitely occurred. It was also concluded that the deblocking reaction got faster with the increase of temperature and the time spent on deblocking reaction was around10min. The TGA results displayed that the blocked isocyanate prepared by different methods with different consumptions of accelerant and stabilizer obtained evidently different thermal properties. At last, it was found that the appropriate NaHSO3/NCO molecular ratio was1.2. While the accelerator consumption was0.2mol and the percent of stabilizer was0.5%, the blocked isocyanate emulsion possessed little size particles and well dispersity. Thereafter, the blocked isocyanate emulsion was washed by different kinds of solvents and then frozen dried. The DSC, TGA, FTIR, XPS and titration analysis methods were employed to characterize the resultant. The experimental results demonstrated that isocyanate could be blocked by sodium bisulfite completely and the deblocking reaction of blocked isocyanate could be accelerated by DMF. The sodium sulfite-blocked isocyanate could be debloced well at the temperature ranging from50to90℃.(2) The emulsified isocyanate was prepared with various methods under different situations. Then the effects of molecular ratio, emulsifier consumption and other factors on stability of emulsion were studied according to the experimental results about emulsifying phenomenon, viscosity and the content of isocyanate group. The experimental results indicated that the emulsion was most stable while the ratio of NCO/OH was50:1and the consumptions of stabilizer and emulsifier were0.9%and2%, respectively. In addition, the particle size distribution of isocyanate emulsion was analyzed. The experimental results showed that viscosity of oligomer, molecular ratio and the content of NCO played important roles on the appearance and distribution of particle size. The smaller the particle size, the more stable the emulsified isocyanate was. The results of particle size were corresponded with viscosity and pot life.(3) The following conclusions were obtained by the study on thermal stability and curing structure of blocked isocyanate modified UF adhesive:Under the optimized conditions, blocked isocyanate (BPI) prepared by synthesis played a catalytic role on the curing rate of UF resin adhesives. BPI has stronger catalysis than ammonium chloride on the UF adhesive curing process. The way that NaHSO3and PAPI were put into UF resin adhesive in the composite has longer curing time, but weak effect in UF curing process. Results of the DSC test show that the curing rate and the curing temperature effect of BPI was better than that NaHSC>3and PAPI were put into UF in the composite. The TGA results show that the blocked isocyanate was added to improve the thermal stability of UF adhesive at proper ratios of2:8. By FTIR analysis, the results show that the BPI compound with UF and UF mixed with NaHSO3and PAPI produce a new chemical bond:carbamate-amino bond, carbamate-methylene bond. Amino and substituted ureas have different absorption strength with different ratio of blocked isocyanate. The XPS analysis show that curing product contains-N-C=O-C and-N-C=O-both in UF adhesives prepared with BPI composite and NaHSO3and p-MDI mixed compound prepared by adding UF adhesive. The-NC=ON functional groups in BPI and UF composite adhesive has more content than that of-NC=OC, which indicating the isocyanate in the BPI has dominant reaction with amino in the UF. The curing product which NaHSO3and p-MDI mixed compound prepared by adding UF adhesive contains more-N-C=O-C than-N-C=O-N, which indicating that the isocyanate in the composite adhesive system has the dominant reaction with hydroxyl group in UF.(4) Meanwhile, a study was taken to test the law of the thermal reaction of emulsified isocyanate modified urea-formaldehyde resin adhesive. By comparing the experiments results, we can get the ratio of emulsified isocyanate compound with the urea-formaldehyde resin and the curing reaction rate and thermal stability of adhesive were affected by acidity of crosslinker. The results showed that emulsified isocyanate added in urea-formaldehyde resin can promote the curing reaction rate and improve the thermal stability of the composite adhesive, but with the ratio of isocyanate emulsion increasing, thermal stability has a downward trend. Acidity of curing agent has a certain impact on isocyanate modified urea-formaldehyde resin. The stronger acid curing agent is, the shorter period of application mixed micelles have. When the catalytic effect of curing agent is weak, the production cannot meet the actual needs, thus ammonium chloride is mixed with formic acid as curing agent (pH=1). FTIR and XPS results show that, EPU was mixed with UF urethane to produce carbamate-amino and carbamate-substituted urea bond; XPS analysis can be used to obtain better characterization of the structure of curing urea-formaldehyde resin modified by isocyanate, and the chemical structure can be quantitatively derived from cured products made by isocyanate and urea-formaldehyde resin.更多还原