Curing kinetics of phenol formaldehyde resin and wood-resin interactions in the presence of wood substrates

The curing kinetics of resol PF resin and resin–wood interactions in the presence of wood substrates have been studied by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The activation energy of cure of PF resin generally increases when PF resin is mixed with wood, mainly due to the decrease of the pH values resulting from the presence of wood. However, wood decreases the curing enthalpy of PF resin through diffusion and the change in the phase of the curing system, which suggests that the curing reactions reached a lower final degree of conversion for the mixtures of PF resin with wood than for the PF resin alone. Moreover, DSC curves and the variation of activation energy with conversion indicate that wood accelerates the addition reactions and retards condensation ones during the curing process of PF resin with wood. The study also revealed that almost no chemical reactions occur between PF resin and wood, but the secondary force interactions of hydroxyl groups between PF resin and wood have been detected. These most significant secondary forces can catalyze the self-condensation reactions of PF resin, although their effect is not vital on the curing kinetics of PF resin.     

Veneer strand flanged I-beam with MDF or particleboard as web material II: effect of resin type,application rate,strand dimension,and pressing time on the basic properties

Optimization of the manufacturing conditions of the veneer strand flanged I-beam invented in the previous study was investigated using different combinations of strand dimensions, resin types between web and flange, different pressing times, and different wood–resin moisture contents under conventional hot pressing conditions. The main results revealed that the strand dimensions have no effect on the bending properties of the flange part and the dimensional stability of the I-beam. Increasing the resin application rate between strands was found to improve the dimensional stability of the I-beams. The use of isocyanate (MDI) resin between web and flange significantly improved the bond strength between web and flange, the modulus of rupture of the I-beam, and the modulus of rupture of the flange part. Dimensional stability was also improved. Shortening the pressing time from 20 to 12min was found to be feasible. Using low wood-resin moisture content was found to interfere with the curing of the phenol–formaldehyde (PF) resin at the flange part resulting in poor quality beams. Of the three moisture content levels tested, 12% was found to be the optimal level for producing I-beams with balanced mechanical properties and dimensional stability.Part of this work was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, March 2003     

Property of nano-SiO2/urea formaldehyde resin

In this paper, we discuss the effects of a nanometer silicon dioxide (nano-SiO₂) coupling agent, dispersal methods and the amount of nano-SiO₂/urea formaldehyde resin. The results of our study indicate that when nano-SiO₂, using KH-550 silane as a coupling agent, was added to UF resin by discontinuous ultrasonic vibration, its properties improved effectively. When the content of nano-SiO₂ was below 1.5%, the amount of free formaldehyde decreased, and the viscosity and bonding strength of resin increased with an increase in the added nano-SiO₂, which did not prolong the curing time. The performance indices of plywood, particleboard and medium density fiberboard (MDF), hot-pressed by nano-SiO2 (1%)/UF resin (F/U molar ratio=1.2), exceeded the requirements of the National Standard. Their free formaldehyde emission reached E1 grade. Finally, we analyzed the mechanism of the strengthening effects of nano-SiO₂ on UF resin by means of infrared spectrum analysis and X-ray photoelectronic spectrum (XPS). __________ Translated from Scientia Silvae Sinicae, 2005, 41(2) [译自: 林业科学, 2005, 41(2)]     

固体核磁共振法对低甲醛释放脲醛树脂化学结构的研究

在采用液体核磁对3种低甲醛释放脲醛树脂化学构造进行分析的基础上,利用13CCP/MASNMR对脲醛树脂固化产物的化学结构进行了研究.结果表明,不同固化体系下,3种低甲醛释放脲醛树脂胶黏剂的固化历程不同,固化后树脂的结构有所差别.不添加固化剂时,脲醛树脂的固化交联反应程度低,固化产物中羟甲基含量高,甲醛释放量也随之增加.加入固化剂后,促进了羟甲基的固化交联反应,脲醛树脂固化产物中羟甲基含量普遍降低.3种固化体系下,UF-3羟甲基含量最高;在氯化铵为固化剂的条件下,UF-2羟甲基含量最低,为0.0582;不添加固化剂和复合固化体系条件下,UF-1羟甲基含量最低,分别为0.0784和0.0713.不同固化体系对不同种类脲醛树脂的固化效果不同,固化后树脂的结构不同,其力学性能和甲醛释放能力也不同.     

Phenol-formaldehyde resin curing and bonding under dynamic conditions

Summary To better understand the curing and bonding behavior of phenol-formaldehyde (PF) resin under dynamic conditions, flakeboards were manufactured either by conventional pressing at 7% or 12% mat moisture content or by steam injection pressing with 10 or 20 seconds steaming duration. Resin-impregnated glass-cloth samples and lap-shear tension specimens were embedded in the core of each flakeboard. After the flakeboards were pressed for various periods of times, the samples and specimens were quickly retrieved. The degree of resin cure was determined on the resin-impregnated glass-cloth samples by dynamic mechanical analysis. The bond strengths were measured from the lap-shear tension specimens on a mechanical testing machine. The results of resin curing and bonding were then correlated to the performance of the resin-bonded boards, which were evaluated by internal bond, modulus of rupture, modulus of elasticity, and thickness swelling. Resin curing and lap-shear bonding did not proceed simultaneously. In conventional pressing, the mat moisture content (MC) at 12% favored resin curing, but slightly retarded lap-shear bonding, as compared to 7%MC. In steam injection pressing, the rates of resin curing and lap-shear bond strength development were much faster for 20 seconds than for 10 seconds of steaming duration. Longer press times were needed to obtain boards with maximum strength in the 12%MC conventional pressing and the 20-s steam duration steam injection pressing than in those conditions where moisture content was lower or steam time was less. The need for longer press times must be attributed to higher internal vapor pressures and/or lower wood and resin component strengths, rather than to incomplete cure or bonding.This material is based on work supported by the Ministry of International Affairs, Quebec Government, the Natural Sciences and Engineering Research Council of Canada, and Laval University (Quebec City). The work was also supported by the U.S. Department of Agriculture under research joint venture agreement FP-92-1835     

三聚氰胺改性低毒脲醛树脂耐水性研究

不同摩尔比的两类低毒脲醛树脂(JQ21未改性,JQ22与5%三聚氰胺共聚),分别与不同质量比的三聚氰胺树脂混合,并在不同的固化体系中固化,用于胶合板的压制.对胶合板的胶合性能及甲醛释放量进行了研究.实验结果表明:固化体系不同,胶接强度也不相同;随着摩尔比的增加,胶接强度提高,甲醛释放量亦相应提高;同时采用共聚和共混两种方法进行改性的脲醛树脂,其胶接强度和甲醛释放量均优于单一的采用共混改性的脲醛树脂;并且混合胶液中三聚氰胺的比例越低,胶接性能越筹,甲醛释放量变化逐渐趋于平稳.     

稻草中密度纤维板用改性脲醛树脂的研究

对比三聚氰胺、二甲基硅油、硅树脂和偶联剂KH-550四种改性剂改性的脲醛(UF)树脂性能的差别及其对稻草中密度纤维板性能的影响,并进行经济评价,最终确定适用于稻草纤维板的改性UF树脂的工艺条件,同时借助于红外光谱(FT-IR)和差热扫描分析(DSC)研究最佳改性UF树脂的结构和固化特性.结果表明,三聚氰胺改性脲醛(MUF)树脂不论是对树脂性能、板性能改善还是从成本分析方面均为稻草纤维板最佳的胶黏剂,FT-IR显示出与未加三聚氰胺相比,加入三聚氰胺后树脂的羟甲基含量降低了10 %,DSC分析则表明其峰值温度有较大幅度的提高,但放出的热量较少.加入三聚氰胺改性的UF树脂其表面张力变小.     

微波等离子处理对脲醛胶性能的影响

脲醛树脂胶粘剂是木材加工领域应用最广泛的胶粘剂,在保障其胶合性能的前提下降低脲醛胶的甲醛释放量是社会关注的焦点和难点。通过试验,研究不同的微波等离子处理方法对脲醛树脂胶粘剂的固化时间、适用期、胶合强度、游离甲醛含量的影响。试验结果表明:等离子处理对脲醛树脂胶粘剂的固化时间和适用期的影响不明显;合适的等离子处理条件可以改善脲醛胶的胶合性能;与未经等离子处理脲醛胶相比,等离子处理后脲醛胶的游离甲醛含量显著降低。     

The influence of curing conditions on the chemical distribution in wood modified with thermosetting resins

Scots pine (Pinus sylvestris L.) sapwood was impregnated with aqueous solutions of phenol formaldehyde and methylated melamine formaldehyde resins and subsequently cured in an oven. One set of specimens was cured in plastic bags to avoid drying (wet curing) while another set of samples was heated and water was allowed to freely evaporate (dry curing). Macroscopic resin distribution was investigated using X-ray densitometry and infrared spectroscopy (FTIR-ATR). During dry curing, the resins migrated to the wood surface resulting in a gradient. Wet curing resulted in even distribution of the resins because it was immobilized due to condensation and precipitation in the wood. Neither densitometry nor FTIR-ATR was found to be generally applicable for investigating resin distribution in modified wood. Wet curing resulted in low cell wall bulking as compared to dry curing, probably because resin precipitated before drying. Storing impregnated wood prior to curing under non-drying conditions (“diffusion phase”) also reduced cell wall penetration and bulking.     

Curing behavior and adhesion properties of epoxy resin blended with polyhydric alcohol-liquefied <Emphasis Type="Italic">Cryptomeria japonica</Emphasis> wood

Cryptomeria japonica (Japanese cedar) wood was liquefied using polyethylene glycol (PEG-400 and PEG-600)/glycerol as the solvent with H₂SO₄ as a catalyst. The blended epoxy resins were prepared by mixing the liquefied wood with epoxy resin of various weight ratios and used for wood gluing. The results showed that blended epoxy resins could cure under room temperature with an exothermic reaction. DSC thermoanalysis showed that increasing the blending amount of liquefied wood would shift the peak of curing reaction to a higher temperature but with less heat released. Blended epoxy resins had a good dry bonding strength for wood when cured at room temperature. However, curing with heat treatment could improve the wet bonding strength of blended epoxy resins, especially for those prepared with PEG-400-liquefied wood.     

硅灰石矿物粉改性脲醛树脂胶黏剂的研究

用未改性硅灰石[Ca_3(Si_3O_9)]矿物粉和硅烷类改性硅灰石矿物粉改性脲醛树脂胶黏剂,研究了硅灰石对脲醛树脂胶黏剂性能的影响和改性脲醛树脂制备的刨花板的胶合性能。研究结果表明,硅灰石矿物粉及其添加量对UF胶的固体含量、pH值、黏度、接触角、固化时间均有一定的影响,所制备的刨花板与用原胶相比胶合性能有不同程度的降低,随着硅灰石添加量的增加,刨花板的吸水厚度膨胀率增加,内结合强度有一定程度下降,但可以达到刨花板国家标准的要求。硅灰石矿物粉作为脲醛树脂胶黏剂改性剂是可行的。     

浅析木材酸性及其对MDF生产的影响

本文对福州人造板厂生产用木片的ｐＨ值、缓冲性能及其对ＵＦ胶固化时间的影响进行了研究，结果表明：木片的ｐＨ值与缓冲性能是影响ＵＦ胶固化的重要因素，煮沸回流后的木片ｐＨ值与ＵＦ胶的固化时间相关性最大；在ｐＨ值相近的情况下，木粉与胶的混合物固化时间随木材缓冲性能的增加而缩短；树皮对胶固化的阻碍大大超过相同ｐＨ值的木材；作为主要原料的马尾松，其地域不同、ｐＨ值不同而呈现出对ＵＦ胶固化的影响也不同。     

Development of a novel polyvinyl acetate type emulsion curing agent for urea formaldehyde resin

High formaldehyde emission and poor water resistance are two main disadvantages of urea formaldehyde (UF) resin. For that reason, a novel polyvinyl acetate (PVAc) type emulsion curing agent was developed in this paper. PVAc type emulsions, including PVAc, the co-polymer of PVAc and N-hydroxymethyl acrylamide (PVAc–NMA), and the ternary co-polymer of PVAc, NMA, and urea (PVAc–NMA–urea), were the main components. Water, aluminum chloride, ammonium dihydrogen phosphate, polypropylene glycol, silicone oil, and urea were the other components. Under heating, aluminum chloride and ammonium dihydrogen phosphate often underwent thermal decomposition and hydrolysis in solution, produce free acid to cure UF resin, so the curing agent could enhance the curing rate, and then shorten the curing time. In this curing agent, ammonium dihydrogen phosphate and urea worked as formaldehyde removers and reacted with free formaldehyde in UF resin, thus the formaldehyde emission exuded from the plywood could be effectively limited and reduced. The bonding strength of plywood was not improved very much, especially the dry bonding strength, but the wet bonding strength was little enhanced for the active hydroxymethyl group contained in PVAc–NMA and PVAc–NMA–urea underwent a self-cross-linking reaction to improve the bonding strength and adhesion force to the bonded substrate. More importantly, the results from the industrial production experiments were shown to be very good.     

Dynamic wettability and curing characteristics of liquefied bark-modified phenol formaldehyde resin (BPF) on rice straw surfaces

Larch bark was liquefied in the presence of phenol and the obtained liquefied resultant was reacted with formaldehyde to prepare the liquefied bark-modified phenol formaldehyde resin (BPF) in an attempt to apply for preparing straw boards. The dynamic wettability of the BPF resin was evaluated on the surfaces of rice straw; either on the alkali solution treated or untreated rice straw surfaces. A new wetting model was employed to quantify the resins’ penetration performances using the spreading–penetration parameters (K value) as a constant to characterize penetration rate. The bigger the K value was, the stronger the penetration and spreading capacity was. Moreover, the curing kinetics of the BPF resin was also investigated with dynamic differential scanning calorimetry. The results showed that the K value of BPF resin was the highest, followed by those of BPF mixed with polymethylene diphenyl diisocyanate PMDI resin and conventional phenol formaldehyde (PF) resin, indicating that the BPF resin had the best wettability. The activation energy of BPF was close to that reported for wood/phenol/formaldehyde resins, but was higher than that of PF resin. The curing reaction was almost complete at 40 % conversion.     

多胺基聚合物改性室温固化型MUF树脂胶黏剂

为解决三聚氰胺-尿素-甲醛(MUF)树脂作为室外级结构集成材胶黏剂时存在的脆性大、易开裂的问题,得到韧性优秀且综合性能满足室外级结构集成材标准的室温固化型MUF树脂胶黏剂,本研究在MUF树脂合成中使用两种改性剂尿素-乙二胺(UE)、尿素-三(2-氨基乙基)胺(UD)分别替代部分三聚氰胺合成了 MUF-UE、MUF-UD...     

Effects of sealed press on improving the properties of particleboard

To improve the properties of particleboard, boards were produced using a sealed press. With the sealed press, boards were processed under high-temperature and high-pressure steam. This increased the saturation temperature, causing a dramatic rise in temperature inside the board, faster curing of the binder, and a shorter pressing time. The boards were bonded with urea formaldehyde resin, melamine urea formaldehyde resin, or poly(methylene diphenyl diisocyanate) (PMDI). The sealed press improved the internal bond strength and thickness swelling of boards regardless of the binder used during the reduced pressing time. The increased bonding strength improved the board properties, allowing PMDI with a lower resin content to be used for bonding the boards.     

生物基本征型阻燃环氧树脂的制备及其性能研究

以香草酸、间二苯酚和表氯醇为原料,采用简单两步法合成了环氧单体1,3,3'-三环氧乙烷-2'-甲氧基-二苯甲酮(DEBP),并进一步和4,4-二氨基二苯砜(DDS)加热混合固化制得对应的环氧树脂DEBP/DDS,与常用的双酚A型环氧树脂(DGEBA)的DDS固化进行对比.研究结果表明:DEBP单体具有比DGEBA单体更...     

胶合板用改性脲醛树脂的调制与应用

分别就改性脲醛(UF)树脂的调胶pH值以及面粉加量对胶液胶合性能的影响进行讨论.结果表明,随着pH值降低,胶合强度和预压强度增大,固化时间和适用期缩短,甲醛释放量降低;面粉用量增大对胶液粘度影响显著,对胶合强度、甲醛释放量有不利影响,但可改善预压性能.综合考虑生产实际,以pH值4.5和面粉加量20%为宜.     

Kraft lignin utilization in adhesives

Summary The utilization of lignin from Pinus radiata black liquor, as a copolymer in ligninphenol-formaldehyde resin binders was studied. Methylolation, demethylation and ultrafiltration separation of high molecular-weight fractions were carried out in order to increase lignin reactivity. The different modified lignins were tested in preparation of lignin-phenolformaldehyde resin binders. Mechanical properties and water resistance were evaluated through testing particleboard panels manufactured with the resins obtained. The best resin was composed of 18,8% ultrafiltrated high molecular weight lignin, 22,9% phenol and 58,3% formaldehyde and had comparable properties with typical commercial resins prepared only with phenol and formaldehyde. An economic analysis was made in order to compare possible benefits obtained through the replacement of phenol by lignin products. The ultrafiltrated lignin copolymer was significantly less costly than a phenol-formaldehyde resin and had comparable physical and chemical properties.The authors acknowledge financial support from the Office of Research, Catholic University of Chile (DIUC) and the National Science Foundation of Chile (CONICYT)     

腰果酚二醚曼尼希碱固化剂的合成及其相分离现象研究

腰果酚(CD)和1,3-二溴丙烷经Williamson醚化反应得到一种腰果酚二醚化合物(CDE),然后以CDE、多聚甲醛和二乙烯三胺为原料,经Mannich反应制备得到一种浅色的腰果酚二醚曼尼希碱固化剂(MBCDE)。通过傅里叶红外光谱(FT-IR)和核磁共振氢谱(~1H NMR)表征了产物的化学结构,并与氨乙基哌嗪(AEP)进行对比研究其相关性能。通过热重分析(TGA)、扫描电镜(SEM)和力学性能测试研究了两种固化剂与双酚A环氧树脂(DGEBA)固化材料的相关性能。结果表明:MBCDE/DGEBA的最大分解温度为351.6℃,具有良好的热稳定性。AEP/DGEBA环氧固化物的冲击强度为3.641 J/m,而添加80%的MBCDE后固化物的冲击强度则为5.155 J/m,提高了41.6%。SEM分析结果表明MBCDE固化材料中存在相分离。