含木质素的发酵残渣在脲醛树脂中的应用研究

对秸秆发酵乙醇残渣进行磺甲基化改性,可有效提高残渣中改性木质素的反应活性;然后将磺甲基化改性发酵残渣用于脲醛树脂(UF)胶粘剂配方中,制备木材用改性UF胶粘剂。结果表明:当m(发酵残渣)∶m(甲醛)=10∶1、m(发酵残渣)∶m(亚硫酸钠)=5∶1和磺甲基化改性发酵残渣替代率为20%时,相应胶合板的各项性能都达到GB/T 14074—2006标准中的指标要求,其水煮3 h后的胶合强度≥0.7 MPa;该改性UF胶粘剂具有制备工艺简单、游离甲醛含量较低等优点,其应用前景良好。     

多羟甲基苯酚改性脲醛树脂的研究

脲醛树脂(UF)是木材工业的主要胶种,为了提高UF的胶接性能和耐水性,同时实现低n(甲醛)∶n(尿素)比例UF中尿素的作用,采用自制的多羟甲基苯酚对UF进行改性,并通过胶合板的压制试验和差示扫描量热(DSC)法来研究改性UF的使用性能。结果表明:多羟甲基苯酚加入时间对UF诸多性能产生明显的影响;当质量分数为10%的多羟甲基苯酚在UF合成末期投入时,所得UF的综合性能相对最佳;与未改性UF胶粘剂压制的胶合板相比,由改性UF胶粘剂压制的胶合板具有相对较高的干强度(1.86 MPa)和湿强度(1.82 MPa),其甲醛释放量降低了30.8%。     

木质素在脲醛树脂胶粘剂中的应用

为解决脲醛树脂(UF)胶粘剂中游离甲醛含量偏高等问题,首先确定了n[甲醛(F)]∶n[尿素(U)]的合适比例,然后以羟甲基化木质素作为UF的改性剂,制备木质素改性UF胶粘剂。研究了木质素的种类及用量对UF各项性能的影响。结果表明:UF中游离甲醛含量随n(F)∶n(U)比例增加而增大;在UF改性过程中,硝酸木质素对游离甲醛的捕捉能力优于硫酸木质素,当w(硝酸木质素)=30%(相对于尿素总质量而言)时,游离甲醛含量(0.126%)相对最低;木质素加入的同时还有助于提高改性UF胶粘剂的胶接强度和耐水性。     

碱性条件下模型化合物UF反应体系的ESI-MS研究

以模型化合物为思维方式,采用电喷雾电离质谱仪(ESI-MS)来研究脲醛树脂(UF)在碱性环境下的相关反应进程和相关机理。研究结果表明,尿素羟甲基化过程是可逆的;碱性条件下羟甲基化可能会形成四羟甲基脲,其中有醚键(-NRCH_2 OCH_2NR-)和桥键(-NRCH_2NR-)。ESI-MS中215、245、275质荷比峰值对应的是醚键结构,227、257质荷比的峰对应的是桥键结构。桥醚键结构的形成具有竞争关系。增加温度对最终UF结构的分布影响不大,但起始反应物摩尔浓度的提高有利于缩聚反应。     

粉状脲醛树脂的制备及性能优化

采用M(三聚氰胺)对UF(脲醛树脂)改性,并经高温干燥过程制备粉状MUF(三聚氰胺改性脲醛)树脂,并对M掺量、M两次添加比例、树脂固含量与固化剂影响MUF树脂性能规律进行探究。结果表明:随三聚氰胺添加量增加,MUF粉状树脂甲醛释放量逐渐降低,胶接强度先增后降,并在w(M)=5%(相对于UF总质量而言)时达到最佳;当M两次添加比例m(M_1)∶m(M_2)=1∶4,树脂胶接强度最大,粉状树脂颗粒均匀,分散性较好;液体MUF树脂固含量为30%时,干燥后制备的粉状树脂胶接强度最大、甲醛释放量最低;m(固体固化剂)∶m(粉状树脂)=15∶100比例混合时,MUF树脂胶粘剂综合性能最佳。     

改性脲醛树脂对提高淀粉胶粘剂耐水性能的研究

为进一步提高淀粉胶粘剂的耐水性能,在传统脲醛树脂(UF)和淀粉胶粘剂合成工艺的基础上,以环氧氯丙烷(ECH)作为UF的接枝共聚改性剂,制备环氧型UF;然后将环氧型UF与传统淀粉胶粘剂进行复配,制备改性淀粉胶粘剂。以耐水剪切强度作为考核指标,采用正交试验法优选出制备改性UF的较佳工艺条件。结果表明:当n(F)∶n(U)=2.0∶1、m(ECH)=8 g、缩聚温度为90℃和接枝共聚时间为75 min时,制成的改性UF可明显提高复配淀粉胶粘剂的耐水性能。     

三聚氰胺共聚改性脲醛树脂固化性能研究

采用M(三聚氰胺)对低n[F(甲醛)]∶n[U(尿素)]比例的UF(脲醛树脂)进行改性,制备了MUF(M共聚改性UF);通过差示扫描量热(DSC)法表征了M的投料时间和比例对UF固化特性的影响,并对MUF的理化性能进行了评价。研究结果表明:随着M掺量的不断增加,MUF胶粘剂的固含量呈增长趋势,固化速率减慢,MUF中游离F含量显著降低。M投料时间对MUF的游离F含量、固含量和固化速率的影响不同,M在缩聚前期投料时,MUF的固含量较高,固化速率基本不变,游离F含量随M掺量增加而逐渐降低;当M在缩聚前期加入且w(M)=3%~4%(相对于U总质量而言)时,MUF中的羟甲基含量相对最低、MUF胶粘剂的综合性能相对最佳。     

硫代硫酸钠/三聚氰胺改性脲醛树脂制备工艺研究

以硫代硫酸钠和M(三聚氰胺)作为复合改性剂,F(甲醛)和U(尿素)作为主要原料,采用弱酸-弱碱-弱酸-弱碱法合成了改性UF(脲醛树脂),并着重探讨了不同因素对UF中的游离F含量、胶合板的胶接强度及F释放量的影响。研究结果表明:合成改性UF的最佳工艺条件是反应温度为85℃,n(F)∶n(U)=1.10∶1,起始pH为5.0,M第2批加入,硫代硫酸钠第4批加入且加入量为U总质量的2%,U分批加入比例为55%、20%、15%和10%;此时UF中的游离F含量(降至0.11%)符合GB/T 14732—2006标准中的指标要求,胶合板的胶接强度(为1.05 MPa)满足国家标准中II类胶合板的指标要求、F释放量(为1.26 mg/L)达到普通胶合板通用技术条件中的E1级指标且耐水性也明显提高。     

超支化聚合物改性UF的研究(I):聚酰胺-胺添加方式对UF性能的影响

以PAMAMs(聚酰胺-胺)超支化聚合物作为UF(脲醛树脂)的改性剂,考察了PAMAMs的添加方式对UF的黏度、固含量、固化时间、固化特性、游离甲醛含量、树脂结构及所制备板材力学强度的影响。研究结果表明:当PAMAMs在缩聚阶段加入时,改性UF的性能相对最好,其黏度下降了1.1 s、固含量增加了3.2%且固化时间缩短了39.1 s,但改性前后游离甲醛含量变化不大;该改性UF的固化速率提高、最大弹性模量增加和固化温度有所下降,并且其结构得到优化,即亚甲基桥键比例增加了86.98%、亚甲基醚键比例下降了29.82%和二羟甲基脲比例提高了1.98%;由该改性UF胶粘剂制备的刨花板,其内结合强度提高了44.9%。     

E_0级中密度纤维板用低成本三聚氰胺改性脲醛树脂的研制

以n(甲醛)∶n(尿素)比例、三聚氰胺用量[相对于改性UF(脲醛树脂)胶粘剂质量而言]作为影响因素,中密度纤维板(MDF)的力学性能和甲醛释放量等为考核指标,采用单因素试验法优选出制备三聚氰胺改性UF胶粘剂的最佳工艺条件。结果表明:该制备方法不添加任何助剂,其最佳工艺条件为n(甲醛)∶n(尿素)=0.95∶1和w(三聚氰胺)=5%;由该胶粘剂压制而成的MDF经穿孔法检测后,其理化性能合格、甲醛释放量低于5 mg/100 g。     

落叶松生物油改性脲醛树脂胶粘剂的制备与性能研究

以自制落叶松热解生物油为原料,采用萃取法制备富酚油;然后以此作为UF(脲醛树脂)的改性剂,考察了富酚油含量对改性UF胶粘剂性能的影响。结果表明:富酚油组分复杂,其中酚类物质含量为53.87%;当w(富酚油)=10%(相对于尿素质量而言)时,改性UF胶粘剂的综合性能较好,由其压制而成的3层杨木胶合板的胶接强度(1.23 MPa)和甲醛释放量(1.05 mg/L)均优于未改性UF胶粘剂。     

Particulate reinforcement and formaldehyde adsorption of modified nanocrystalline cellulose in urea-formaldehyde resin adhesive

In this study, nanocrystalline cellulose (NCC) was used for reinforcement and formaldehyde (HCHO) adsorption of urea-formaldehyde (UF) resin adhesive in fiberboard. The original NCC was modified by 3-aminopropyltriethoxysilane for improving the wetting property with UF resin adhesive. The UF resin adhesive with modified NCC was analyzed by X-ray powder diffraction, thermogravimetric analysis, and Fourier transform infrared. The HCHO emission and bending and bonding strength of the UF resin adhesive with modified NCC were tested according to Chinese National Standard GB/T 17657-1999. Compared with the original UF resin adhesive, modified NCC led to limited effects on the crystal structure, thermal stability, and characteristic absorption peaks of UF resin adhesive. The HCHO emission of the UF resin adhesive with 1.0% modified NCC decreased by 13.0%, while the bending and bonding strength increased by 40.5 and 158.3%, respectively. The improvements of modified UF resin adhesive were destroyed by the reunion of NCC when the content was more than 1.5%.     

基于改性橡子淀粉制备的UF胶粘剂用填料性能研究

以改性橡子淀粉、茶叶废料粉和无机矿物粉组成的复合无机填料作为面粉的替代物,配制胶合板用脲醛树脂(UF)胶粘剂。着重探讨了复合无机填料的种类及含量对UF胶粘剂和胶合板的固化速率、预压性能、热稳定性能、胶合强度及其甲醛释放量等影响。结果表明:以复合无机填料替代面粉制成的胶合板用UF胶粘剂,具有预压性能良好、胶合板胶合强度更高且甲醛释放量更低等优点,其应用前景良好。     

淀粉标签胶耐水性的改性研究

木薯淀粉经H2O2氧化后,在糊化过程中以H3PO4为酸催化剂,通过添加甲醛和尿素进行复合改性,由此制备出一种改性氧化淀粉粘合剂;然后将其分别与苯丙乳液(SAE)、脲醛树脂(UF)、改性脲醛树脂(M-UF)和SAE/M-UF进行交联复配制取标签用复合粘合剂,并利用傅里叶红外光谱(FT-IR)技术分析了交联复配过程中基团的变化情况。结果表明:改性氧化淀粉粘合剂的脱标时间为2h;相应的复合粘合剂的脱标时间分别为6、24、48、73h,即均能满足现代标签胶的使用要求;-OH伸缩振动吸收峰在复配过程中有变窄的趋势;反应过程中生成的UF在1550～1650cm-1附近出现了2～3个新的吸收峰,分别对应C-N和-NH-的伸缩振动吸收峰;复配过程中引入的SAE会在1750cm-1附近出现酯基的吸收峰。     

Reduction of Formaldehyde Emission from Particleboard by Phenolated Kraft Lignin

The aim of this study was the reduction of formaldehyde emission from particleboard by phenolated Kraft lignin. For this purpose, the lignin was extracted from black liquor and then modified by phenolation. During the urea formaldehyde (UF) resin synthesis different proportions of unmodified and phenolated Kraft lignins (10%, 15%, and 20%) were added at pH = 7 instead of the second urea. Physicochemical properties and structural changes of resins so prepared, as well as the internal bond (IB) strength and formaldehyde emission associated with the panels bonded with them were measured according to standard methods. The Fourier transform infrared (FTIR) analysis of lignin indicated that the content of O–H bonds increased in phenolated lignin while the aliphatic ethers C–O bonds decreased markedly in the modified lignin. Since both synthesis of UF resins and lignin phenolation are carried out under acid conditions, phenolation is an interesting way of modifying lignin for use in wood adhesive. The panels bonded with these resins showed significantly lower formaldehyde emission compared to commercial UF adhesives. The UF resin with 20% phenolated lignin exhibited less formaldehyde release without significant differences in internal bond strength and physicochemical properties compared to an unmodified UF resin. XRD analysis results indicated that addition of phenolated lignin decreased the crystallinity of the hardened UF resins.     

Differential scanning calorimetry and dynamic mechanical analysis of amine-modified urea–formaldehyde adhesives

Urea–formaldehyde (UF) resins are susceptible to stress rupture and hydrolytic degradation, particularly under cyclic moisture or warm, humid conditions. Modification of UF resins with flexible di- and trifunctional amines reduces this problem. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to study the thermal behavior of modified and unmodified adhesives to identify the physical and morphological factors responsible for the improved performance. A UF resin modified by incorporating urea–capped poly(propyleneoxidetriamine) during resin synthesis exhibited a higher cure rate and greater cure exotherm than the unmodified resin. Resins cured with a hexamethylenediamine hydrochloride curing agent had slower cure rates than those cured with NH₄Cl. DMA behavior indicated that modified adhesives were more fully cured and had a more homogeneous crosslink density than unmodified adhesives. DMA behavior changed with storage of specimens at 23°C and 50% relative humidity, after previous heating for approximately 20 min at 105°C to 110°C. The initial changes were postulated to occur because of physical aging (increase in density) and continued cure. These were followed by physical breakdown (microcracking) and possibly cure reversion. © 1995 John Wiley & Sons, Inc.     

Thermoplastic modification of urea–formaldehyde wood adhesives to improve moisture resistance

Urea–formaldehyde (UF) resins are prone to hydrolytic degradation, which limits their use to indoor applications. This study examined the modification of UF resin with various thermoplastics as a means to increase the moisture resistance of the adhesive. UF adhesives were modified in situ with various hydrophobic and hydrophilic thermoplastic formulations, using either polar or nonpolar initiators. Unmodified and modified UF resins were characterized in terms of viscosity, pH, and gel time in their prepolymer suspension state. Cured solid UF resin plaques were prepared to isolate moisture sorption effects of the cured UF resin from that of the wood component in composites, which dominates their moisture uptake. Relative crosslink density and moisture sorption tests were run on cured UF resin plaques. Results indicated that viscosity increased after modification in most cases, with higher viscosities resulting from formulations using an acidic (polar) initiator. In all cases, activation energies of the curing reactions of thermoplastic‐modified UF suspensions were lower than the unmodified UF. High relative crosslink density compared to the unmodified UF was found for one sample, which correlated well with lower overall moisture sorption. Higher relative crosslink density of cured UF resin plaques appeared to be an indicator of lower moisture uptake. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4222–4229, 2006     

Thermoplastic polymers as modifiers for urea–formaldehyde wood adhesives. III. In situ thermoplastic‐modified wood composites

Acrylic monomers and free‐radical initiators were dispersed in an aqueous urea–formaldehyde (UF) suspension and polymerized in situ to afford a suspension containing 5 wt % thermoplastic (5 g of thermoplastic/100 mL of suspension). The viscosity of the thermoplastic‐modified UF suspension (65 wt % solids at 25°C) ranged from 240 to 437 cP versus 121 cP for the unmodified UF control. Wood‐flour composites (sugar maple and 50 wt % adhesive) were prepared with thermoplastic‐modified UF suspensions and cured with the same cycle used for the composites prepared with the unmodified UF adhesive (control). The effect of the thermoplastic‐modified UF adhesive was evaluated on the notched Izod impact strength and equilibrium moisture uptake of the wood‐flour composites. The notched Izod impact strength of the composites prepared with modified UF adhesives increased by as much as 94% above that of the control. The increase depended on the initiator and the monomer composition. The modification affected the equilibrium moisture uptake and rate of moisture uptake in the wood‐flour composites. Preliminary results for particleboard prepared with 10 wt % modified UF adhesive (5% thermoplastic in the UF resin) and unoptimized cure conditions confirmed a significant effect of the thermoplastic modification on both the internal‐bond strength and thickness swelling of the particleboard. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008