三聚氰胺/纳米TiO_2联合改性脲醛树脂胶粘剂研究

以甲醛、尿素为原料,纳米TiO_2和三聚氰胺为改性剂,采用"碱-酸-碱"的合成工艺合成脲醛树脂,并对三聚氰胺/纳米TiO_2联合改性脲醛树脂工艺进行优化。研究结果表明:当纳米TiO_2用量不变,脲醛树脂的黏度、固含量、胶合强度随三聚氰胺加入量增加而增大,而固化时间和游离甲醛含量则呈现出相反的变化趋势;添加w(三聚氰胺)=1.5%(相对于尿素添加质量而言)改性后的脲醛树脂游离甲醛含量为0.41%,耐水胶合强度为1.25 MPa,对不同配比的甲醛/尿素(F/U)脲醛树脂,三聚氰胺/纳米TiO_2联合改性性能相似;改性后的脲醛树脂及纳米TiO_2能够均匀分布于木材表面,以保证较好的胶合强度和联合改性效果。     

酸-碱-酸-碱工艺合成脲醛树脂

以酸-碱-酸-碱工艺合成一种聚乙烯醇(PVA)、三聚氰胺改性脲醛树脂,研究了原料配比、pH值、反应时间等对产品性能的影响。结果发现,当n甲醛:n尿素=1.6:1,聚乙烯醇加入量为甲醛和尿素总质量的1%,三聚氰胺加入量为甲醛和尿素总质量的3%,酸性条件下pH=5.5,碱性条件pH=8.5～9.0,反应温度为80℃左右时,合成的脲醛树脂的机械强度较好,游离甲醛的含量较低。     

苯酚/甘脲改性脲醛树脂胶黏剂的制备及性能研究

以尿素和甲醛为原料、苯酚/甘脲为甲醛捕收剂制备脲醛树脂(UF)。增加苯酚/甘脲用量,脲醛树脂中游离甲醛的质量分数降低,固化时间增加。增加缩聚时间,脲醛树脂的黏度增加,游离甲醛的质量分数降低。研究结果表明,当苯酚质量分数为0.5%、甘脲质量分数为0.5%、三聚氰胺质量分数为1%、缩聚时间为20 min时,采用一次性加入甲醛、分批次加入尿素和改性剂的碱-酸-碱合成工艺制备的UF中的游离甲醛的质量分数约为0.042 6%,远低于浙江DB33-T-494的E1级指标。     

脲醛树脂的合成及其性能研究

以尿素和甲醛为原料合成脲醛树脂,探究了不同合成条件对产物性能的影响。结果表明:采用碱-酸-碱合成工艺,尿素分两次加入的合成方法,原料尿素与甲醛的摩尔比为1:2.65,原料的pH值为7.7,改性剂三聚氰胺,95℃下反应2h。合成的脲醛树脂的游离醛含量为4.96%,固体含量高达46.56%。     

苯酚-尿素-甲醛三元共缩聚树脂合成工艺的研究

针对脲醛树脂在制板过程以及人造板材在使用过程中不断释放甲醛。危害人体健康的环保问题,以及耐水、耐老化性能差的缺点。以苯酚、尿素和甲醛为原料,采用高温（90℃）缩聚反应合成苯酚-尿素-甲醛共缩聚树脂（PUF胶黏剂）,缩短了反应时间,提高了耐水、耐老化性能,且游离甲醛含量〈O．3％,游离苯酚含量〈0．5％。对树脂的结构和性能进行全面的分析,得出当甲醛、尿素、苯酚摩尔比为10：8：1时树脂性能最佳,压制的胶合板力学性能好,板材甲醛释放量达到GB18580—2001中E2级水平。     

苯酚/聚乙烯醇改性脲醛树脂胶粘剂的制备及性能研究

以苯酚和聚乙烯醇(PVA)作为改性剂,采用正交试验法探讨了最终n(甲醛)∶n(尿素)、苯酚含量以及PVA含量对脲醛树脂(UF)的游离甲醛含量和胶接强度的影响。研究结果表明:当最终n(甲醛)∶n(尿素)=1.2∶1、w(苯酚)=20%和w(PVA)=1.0%(均相对于尿素总质量而言)时,苯酚/PVA改性UF的游离甲醛含量、胶接强度等均能满足GB/T 14732—2006标准中Ⅱ类胶合板的要求,并且相应胶合板的甲醛释放量(为1.70 mg/L)远低于GB/T 9846.3—2004标准中E2级指标要求。     

低含量游离甲醛脲醛树脂胶

本文提出采用降低甲醛与尿素摩尔比;尿素多次加入;控制缩聚反应较低PH值的方法合成低含量游离甲醛的脲醛树脂胶。经测试:粘接强度较高,性能稳定,游离甲醛含量较低。     

苯酚改性脲醛树脂泡沫耐水性的研究

研究了用苯酚改性脲醛树脂发泡的合成工艺。探讨了甲醛、尿素和苯酚的摩尔比脲醛树脂胶黏剂运动黏度的影响,比较了改性前后脲醛树脂泡沫吸水率的变化。结果表明:甲醛与尿素的摩尔比为1.4∶1,苯酚量为尿素的3%时,制得的脲醛树脂的性能良好,符合脲醛树脂的国家标准GB/T14732-2006要求。发泡后的脲醛树脂泡沫耐水性提高。     

脲醛树脂胶粘剂~(13)C核磁共振分析

采用常规化学分析和13C核磁共振相结合的方法,分析研究了脲醛树脂胶粘剂性能与结构的关系。结果表明:在摩尔配比F:U=1.2:1时,粘度越高,游离尿素的含量越低,羟甲基的含量越低,游离甲醛含量降低; 树脂产品的粘度低,聚合度也低,羟甲基的含量偏高,粘接性能下降,同时游离甲醛含量上升,而适量苯酚的添加可改善树脂结构,是一种优化树脂的途径。当增大摩尔配比到F:U=1.4:1时,尿素含量下降,游离甲醛含量上升。因此,摩尔配比的选择在很大程度上影响脲醛树脂的性能。     

脲醛树脂的合成及其在堵水中的应用

本文以尿素和甲醛为主要原料来合成脲醛树脂,考察了甲醛和尿素的摩尔比、尿素加入方法、改性剂加量等对树脂中的游离甲醛含量以及树脂稳定性的影响,优化了合成条件。以氯化铵为固化剂,六次甲基四胺为固化速度调节剂对合成的脲醛树脂进行固化。通过性能评价,发现脲醛树脂的固化时间在较大范围内可以调节;固化后抗压强度高;在地层液体中具有低的溶解率;采用加入增孔剂的方法成功的使脲醛树脂具有了选择性。     

低毒脲醛树脂胶粘剂的研究进展

综述了低游甲醛脲醛胶粘剂的合成技术,对原料摩尔比、改性剂、缩聚工艺、甲醛捕捉剂等因素进行了讨论。     

环保型脲醛树脂胶粘剂的制备研究

脲醛树脂是广泛用于木材工业中一种重要的胶粘剂,影响脲醛树脂甲醛含量的因素有多个方面,为寻求合适的工艺条件以提高脲醛树脂胶粘剂的综合性能,通过改变尿素与甲醛的摩尔质量比及控制反应时间等途径优化了环保型脲醛树脂胶粘剂的合成方法.实验结果表明:在U/F=1:2.0,pH达到5～6时反应40分钟,此时的胶粘剂甲醛含量与粘性的综合情况最佳.     

脲醛树脂胶粘剂复合改性研究

脲醛树脂(UF)胶粘剂是一种由尿素与甲醛通过缩聚反应而合成的热固性树脂,广泛应用于木材加工及涂饰行业。针对目前市售脲醛树脂存在的一些问题如游离甲醛含量高、耐水性差、贮藏稳定性差等进行了研究,在探讨合成机理的同时,通过分别加入聚乙烯醇(PVA)、糠醛、硫脲以及由PVA、糠醛和硫脲组成的复合改性剂对树脂进行改性。研究结果表明：复合改性剂的加入,使得改性合成的UF树脂在游离甲醛含量、耐水性、贮藏稳定性等方面优于未改性的UF树脂。     

Synthesis of urea-formaldehyde resin by melt condensation polymerization

Traditional method of synthesizing urea-formaldehyde (UF) resins is condensation polymerization with formaldehyde and urea in aqueous solution, which leads to the low resistance of UF resins against the influence of water and moisture and results in the high formaldehyde emission. A new method of melt condensation polymerization was used to synthesis UF resin by paraformaldehyde with urea. Fourier-transform infrared spectroscope and Carbon-13 nuclear magnetic resonance were performed to elucidate the uron rings structural characteristics of UF resin by the synthetic route. The stability during storage and application were characterized by measuring concentration of methanol and free formaldehyde, and DSC and TG analysis, respectively. The results show that UF resin synthesized by melt condensation polymerization has lower content of free formaldehyde, high thermal stability and better stability during storage.     

改性脲醛树脂泡沫塑料的制备

采用加入木质素磺酸钠改性脲醛树脂,以降低游离甲醛含量及充分利用木质素资源;同时加入三聚氰胺和聚乙烯醇,以改变树脂的柔韧性。通过碳酸氢铵发泡法发泡制得开孔改性脲醛树脂泡沫塑料。实验结果表明:改性后游离甲醛含量明显降低,韧性有了较大的提高。     

Influence of glyoxal on curing of urea-formaldehyde resins

In the present paper, the effect of glyoxal on the gel formation within the adhesive systems based on urea-formaldehyde (UF) resins is shown. A reduction of formaldehyde content in wood-based panels by decreasing the formaldehyde/urea molar ratio in the UF resins leads to increasing of the UF resin gel time, and impairing the qualitative characteristics of the UF-based wood materials. Glyoxal is shown to speed up the crosslinking of the macromolecules as well as significant reduction of gel time of adhesive composition. The first reason is the result of reaction between glyoxal and ammonium ion leading to protons releasing. Another reason is that glyoxal and its interaction products react with macromolecules of the UF resin forming a three-dimension cross-linked structure. The gel time and the pot life of the UF resin are measured by the oscillatory viscometer. Formation of the UF cross-linked resin structure with glyoxal and a curing catalyst (ammonium sulfate) is studied using dispersion Raman scattering spectroscopy. Particleboards (PB) are produced using different amount of glyoxal and formaldehyde/urea molar ratio in the UF resin. The properties are evaluated according to the European Standards and include density, internal bond, thickness swelling moisture content and formaldehyde content.     

Influence of Ammonium Pentaborate (APB) on the Performance of Urea Formaldehyde (UF) Adhesives for Plywood

Ammonium pentaborate (APB) was used to modify urea formaldehyde (UF) resins, in which the formaldehyde to urea molar ratio was set at 1.80, 1.50, 1.25, and 1.05. Some specific properties, including gel time, free formaldehyde content in UF, bond strength, and formaldehyde emission levels from plywood were evaluated. The result showed that APB increased the gel time length, but also decreased free formaldehyde content and emission levels, which was reduced mostly by 79.0% and 81.4%, respectively. The result of bond strength indicated that APB was proper to modify high F/U molar ratio of UF resin regardless of the loading level, but a recommended loading level should be considered to relevantly lower the F/U molar ratio of UF. The suggested loading level of APB to UF is 8.0% to 6.0%, 6.0%, and 4.0% to UF resin with F/U molar ratio of 1.8, 1.5, and 1.25 separately.     

Influence of acrylamide copolymerization of urea–formaldehyde resin adhesives to their chemical structure and performance

To lower the formaldehyde emission of wood‐based composite panels bonded with urea–formaldehyde (UF) resin adhesive, this study investigated the influence of acrylamide copolymerization of UF resin adhesives to their chemical structure and performance such as formaldehyde emission, adhesion strength, and mechanical properties of plywood. The acrylamide‐copolymerized UF resin adhesives dramatically reduced the formaldehyde emission of plywood. The ¹³C‐NMR spectra indicated that the acrylamide has been copolymerized by reacting with either methylene glycol remained or methylol group of UF resin, which subsequently contributed in lowering the formaldehyde emission. In addition, an optimum level for the acrylamide for the copolymerization of UF resin adhesives was determined as 1%, when the formaldehyde emission and adhesion strength of plywood were taken into consideration. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Urea impregnated multiwalled carbon nanotubes; a formaldehyde scavenger for urea formaldehyde adhesives and medium density fiberboards bonded with them

Multiwalled carbon nanotubes (MWCNTs) were subjected to modification by urea to use as formaldehyde scavenger in urea formaldehyde (UF) adhesive and reducing the free formaldehyde emission of the medium density fiberboards (MDFs). Morphological differences besides elemental analysis was investigated using field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy. The effect of urea impregnated MWCNTs filler on the physical, morphological and thermal properties of the UF resin has investigated. Furthermore, characterization of the mechanical properties, free formaldehyde emission and thickness swelling were carried out for the MDF panels. From the results, the free formaldehyde of the UF resins was significantly decreased. The lowest free formaldehyde was belonged to the sample with 3 wt% of scavenger which was about 71% lower than the value for neat UF resin. Accordingly, the formaldehyde emission of the fiberboards was also showed a descending trend by incorporation of MWCNTs-U to the composite structure. It was decreased from 9.67 to 3.89 mg/100 g dried board. These results indicated that the prepared nano modifier was successfully performed as a formaldehyde scavenger for the UF resin and could prevent the hazards of the free formaldehyde emission from MDF panels.