纸页水分含量对纤维相对结合面积和剪切抗张强度的影响

本文以PAGE方程为基础，结合光散射系数测量技术，并以针叶木为原料，研究了水分含量对纤维剪切结合强度和相对结合面积（Relative Bonded Area）RBA的影响。实验表明，一定的水分含量下剪切结合强度达最大值，RBA随着水分和打浆度的增大而增大。     

什么使生活用纸具有如此特殊的性能?取决于纤维

<正>纸浆的性能主要取决于原材料、制浆过程、脱木素程度以及采用的漂白工序。对于应用于生产纸及纸板的纸浆,强度性能非常重要(见表1)。在造纸过程中,增加纸张强度的方式有好几种,如打浆、湿压榨、干燥和改进浆料配比,比如提高长纤维比例,减少惰性填料用量或者使用增强剂。为了获得性能良好的纸/纸板,化学浆的打浆是很有必要的。纸张的结合能力、密度和强度随着打浆度增加而增加,但是脱水阻力也会增大。打浆使纤维内部产生帚化,使纤维更柔韧,这就使得纤维之间结合更好,接触面积也相应增加。     

高湿强特种纸的研究

以一种低定量特种纸为研究对象,对纤维原料、打浆工艺、多元增强体系和特种增强纤维进行研究,研发高湿强特种纸。结果显示:雄狮浆成纸抗张强度优于思茅松浆;随着打浆度的提高,雄狮浆产生切断、压溃、润胀和分丝帚化,有利于对化学助剂的吸附,增加成纸纤维间结合点;多元增强体系增加PAE的留着,特种增强纤维水溶PVA纤维起到纤维粘结剂的作用,提高成纸的湿强度。     

添加干强树脂提高纸强度的机理

通过分析纸的基本机械和光学性能，来研究添加聚丙烯酰胺干强树脂(PAM)增加纸强度的作用机理。对添加不同量PAM的轻打浆的阔叶木硫酸盐浆手抄纸页与不同打浆度的同种纸浆的手抄纸页进行了比较。断裂韧度在低量添加PAM时会增加，随着进一步的添加会趋向平稳，抗张强度则随着PAM留着量的增加而增加。添加PAM和打浆对断裂韧度和抗张强度的增加有同样的效果。另一方面，由PAM留着量的增加引起的纸张紧度、杨氏模量和RBA(相对结合面积)的提高，与由增加打浆度引起的提高相比要小得多。纤维结合面积在张力负荷下的逐渐减少，表现为纤维间的光学接触面积的减少，这是通过在黑色衬背下同步测量光的反射率(R。)研究的。对含有PAM的纸页来说，从加载到断裂R0的增加很小，并且保持稳定、与PAM的留着量无关；而对重度打浆的纸页来说，R0的增加相对要大，并且随着打浆度的增加而增加。这些结果表明：添加PAM引起的强度的提高主要归因于单位结合面积的结合强度的增加；而通过打浆引起的强度提高要归结于纤维结合面积的增加。     

影响湿纸幅强度主要因素的研究进展

本文综述了抄纸过程中湿纸幅强度的重要性、湿纸幅强度形成的机理以及提高湿纸幅强度的技术和方法。纤维间的缠结、摩擦和结合力是影响湿纸幅强度的主要因素,同时浆料种类、打浆度、聚合物助剂、微纤化纤维素(MFC)、填料等对湿纸幅强度也有一定影响。     

纤维素酶促打浆对漂白针叶木浆湿部电荷特性的影响

采用纤维素酶处理漂白针叶木浆,然后进行打浆,研究了酶促打浆对浆料湿部电荷特性的影响.并对纤维素酶促打浆后纸浆的打浆度、纤维特性、黏度及物理强度等进行了分析.结果表明,采用纤维素酶对漂白针叶木浆进行打浆前预处理,可以促进纤维的润胀和分丝帚化,提高纤维的比表面积和纸浆打浆度.并可减少纤维的切断作用,降低细小纤维含量.酶促打浆浆料中的溶解电荷及纸浆的Zeta电位略低于对照浆,有利于填料在纸浆中的留着.     

机械木浆纤维形变性表征及其对纤维间结合性能的影响

针对不同木素含量的纤维原料,采用不同评价方法对其形变性能进行表征,包括纤维柔软性(F)、纤维横截面纵横比(AR)和纤维压溃指数(CI);同时围绕纤维形变性对纤维间结合性能以及手抄片物理强度的影响进行分析。结果表明,F、AR和CI都可以用来表征纤维的形变性,其中,当木素含量从24.28%减少到2.67%时,F表征的相对形变量为956.5%,数倍于其他两者,说明F这一指标表征的更为全面;随着F从0.516×10~(12)N~(-1)·m~(-2)增加到5.454×10~(12)N~(-1)·m~(-2),纸张中纤维间的相对结合面积(RBA)和剪切结合强度(b)增大,Page结合强度指数从3.60 N·m/g线性增加到84.07 N·m/g;在纸张成形过程中,可以通过改变纤维形变性能调节纸张强度和松厚度之间的对立关系。     

纸张干强剂的研究

我国木浆特别是长纤维木浆短缺,许多纸种需配用短纤维阔叶木浆、草浆和回收纸浆,这势必导致纸张强度下降,所以有必要采取措施提高纸张强度。纸的强度受纤维间结合强弱控制。纤维间结合强度与结合部分形成的氢键数量和质量有直接关系,应用纸张增强剂是加强纤维间结合的好办法,可以避免提高打浆度引起的纸的紧度升高,湿变形增大,不透明度、吸收性、透气度乃至撕裂度下降。犤1犦目前主要使用的纸张增强剂按功能来分类可分为干增强剂和湿增强剂。干强剂主要有淀粉,变性淀粉,植物胶,聚乙烯醇和聚丙烯酰胺(PAM)等,其中使用最普遍的是PAM和阳离…     

利用中浓打浆提高质量降低能耗

打浆是制浆造纸的重要环节,优良的打浆工艺依赖于良好的打浆设备和合理的工艺操作来实现,而打浆浓度又是打浆过程中应该很好控制的重要参数。目前国内多数纸厂采用的低浓双盘磨打浆,对纤维的剧烈切断所引起的纸页强度较差,及比较高的能耗都使企业的生产处于不利的境况。中浓打浆与低浓打浆相比具有很多优点：提高纤维的细纤维化程度,减少纤维的切断,较好地保留纤维的强度。一般认为影响成纸强度的主要因素是纤维间平均结合力的大小和纤维的平均长度。影响纤维间平均结合力的是纤维的氢键结合程度,而细纤化程度则是氢键形成的主要影响…     

打浆对思茅松纤维动态力学性能的影响

本文通过对云景思茅松硫酸盐浆进行打浆和抄纸实验,考察了纤维形态在打浆过程中的变化规律;研究了不同打浆方式、打浆度对成纸动态力学性能的影响。结果表明:PFI打浆有利于提高思茅松纤维成纸的抗张强度和耐破强度;Valley打浆对纸页动态力学性能的影响要明显优于PFI打浆;思茅松纤维有利于提高纸页的动态弹性模量和损耗因子。     

Hydroxymethylated resorcinol (HMR) priming agent for improved bondability of wax-treated wood

The effects of hydroxymethylated resorcinol (HMR) on the tensile shear strength of wood joints treated with montan ester wax were studied with polyvinyl acetate (PVAc) and melamine formaldehyde (MF) adhesives. Untreated specimens which were bonded with MF and PVAc had similar bond strength properties under dry conditions, but MF bonded specimens’ tensile shear strength values were higher than that of PVAc glued specimens under wet conditions. With both adhesives tested, dry tensile shear strengths of wax-treated specimens were in a comparable range to those of untreated wood, while under wet conditions the strength values of wax-treated specimens were significantly lower than those of the controls. HMR priming increased the shear strength of PVAc bonded specimens under wet conditions and of MF-bonded specimens under dry and wet conditions. The effect on MF-bonded specimens, however, was much more pronounced under wet conditions.     

不同制备方式得到的MFC的增强应用对比

分别采用TEMPO诱导氧化预处理结合机械研磨法和PFI磨精浆法制备了2种微纤化纤维素(分别记作TO-MFC和PR-MFC),比较了TO-MFC和PR-MFC作为增强剂对抄纸过程的影响及对纸张的增强效果。研究表明：加入3%的TO-MFC或PR-MFC后,浆料滤水速度变慢,填料留着率提高,纸张强度性能提高,其中,抗张强度增幅最大,TO-MFC的增强效果略好于PR-MFC。TO-MFC和PR-MFC均为纳米级纤丝交织形成的网络状结构体,与纸浆纤维之间有很强的结合力,提高了纸张的强度性能。     

Bonding surface-modified Karri and Jarrah with resorcinol formaldehyde

A series of abrasive papers were used to sand machined regrowth karri (Eucalyptus diversicolor) and regrowth jarrah (E. marginata) wood surfaces. Shear test specimens were then prepared by gluing sanded wood blocks with resorcinol-formaldehyde and pressing them at 1500 kPa and 20°C for 7 hours. Wettability measurements on sanded wood surfaces and strength tests on shear test specimens were used to assess the ability of the sanding treatment to improve adhesive performance. The effect of sanding on wettability and shear strength varied according to the abrasiveness of the sanding treatment. Application of the coarsest abrasive (80 grit) significantly improved wettability and shear (adhesive) strength in both dry and wet conditions. A positive correlation between wettability and shear strength occurred only after sanding. SEM observations revealed different morphological structures of the glueline in sanded and non-sanded surfaces.     

Influence of processing parameters and wood properties on the edge gluing of green <Emphasis Type="Italic">Eucalyptus grandis</Emphasis> with a one-component PUR adhesive

The predominant plantation hardwood species in South Africa Eucalyptus grandis is, despite relatively good strength and stiffness properties, seldom used for lumber production due to low dimensional stability, splitting, and cracking of the wood. As critical defects often develop or aggravate during the drying process, the edge gluing of Eucalyptus grandis lumber in its wet state, before kiln-drying, was considered a potential inhibiting factor for this behaviour. The objective of this study was to determine how certain material and processing variables influence the bond quality of unseasoned, edge-glued, Eucalyptus grandis, using a moisture-curing one-component polyurethane adhesive. The study considered the effect of four parameters, namely wood density, moisture content, adhesive spread rate and pressure, on the shear strength of bondlines. Micro computed tomography scanning was used to observe adhesive penetration behaviour. Overall, the bonding quality was satisfactory proving the feasibility of edge gluing of this wood in the wet state. Multiple ANOVA showed that generally better results were obtained for samples with a higher moisture content of roughly 60% compared to specimens with lower moisture content around fibre saturation point. Results indicated that the lower spread rate tested (150 g m^?2) should be preferred to the higher one (250 g m^?2), since it will likely give more stable shear strength results and it would be preferable from an economic point of view. Increasing pressure did not increase the shear strength significantly.     

The long-term evaluation of FRPs bonded to timber

This research investigated the long-term environmental effects on bond strength at the interface between fiber- reinforced polymers (FRPs) and timber. A total of 581 timber specimens were bonded with seven types of FRP sheets (unidirectional and bidirectional glass, carbon, aramid, and hybrids) using a wet lay-up technique. The specimens were exposed to acidic, alkaline, fresh water, and sea water solutions with pH of 2.5, 7, 7.25, 10, and 12.5 for 1, 3, 6, 9, and 12 months. A chamber was also used to simulate ultraviolet radiation after 6 months. A series of single-lap shear tests were then conducted to determine the interfacial bond strength reduction. The results showed that bidirectional carbon and glass FRP sheets demonstrated better bond strength as compared to unidirectional carbon and glass FRP sheets in most cases after exposure to the chemical solutions and ultraviolet radiation. Moreover, acidic and sea water solutions, respectively, had the most and the least effects on the reduction of bonds at the interface between hybrid FRPs and timber. Meanwhile, bidirectional aramid FRPs showed high deterioration in the interfacial bond strength under the effect of water and alkaline (pH 12.5) solutions. Finally, the failure modes on timber substrates were explored and classified.     

湿炼及油浸提两种方式对猪油品质的影响

以猪背脂为原料,采用110、120、130、140℃湿炼及油浸炼制猪油,测定了猪背脂出油率以及油脂的水分含量、酸价、丙二醛含量、过氧化值等理化指标,研究两种加工方式对猪油品质的影响.结果表明:在同一炼制温度条件下,达到最大出油率的时间湿炼比油浸提明显延长;随炼制温度提高出油率上升,140℃条件下的猪油提取率达到最高,为69%;除140、110℃湿炼外,其他加工条件所得猪油均达到国家一级食用猪油标准.     

Hydroxymethylated resorcinol (HMR) priming agent for improved bondability of silicone modified wood glued with a polyvinyl acetate adhesive

A hydroxymethylated resorcinol (HMR) was used as a coupling agent to improve glueability of silicone (aminofunctional polydimethylsiloxane) modified pine sapwood (Pinus sylvestris) with polyvinyl acetate (PVAc). Priming with HMR did not significantly increase tensile shear strength of unmodified and silicone treated wood under dry conditions. Under wet conditions, tensile shear strength of the control specimens was increased by 37% and of the silicone modified specimens by 13%. Despite of higher shear strength under wet conditions, the primed silicone treated specimens displayed lower degree of wood failure than the unprimed treated specimens.     

喷水工艺对木质素胶黏剂刨花板性能影响的研究

就板坯制备工艺对采用木质素胶黏剂制备刨花板进行试验研究,通过设计正交试验,获取和分析所制备刨花板的物理力学性能,探讨制板工艺过程对木质素胶黏剂刨花板性能的影响。试验结果表明,制板过程中,采用喷水工艺对木质素胶黏剂刨花板的静曲强度和弹性模量影响最大,对24 h吸水厚度膨胀率影响次之,对内结合强度影响较小;随着喷水量的增大,静曲强度、弹性模量和内结合强度呈下降趋势,24 h吸水厚度膨胀率先增大后减小。在本试验范围内,木质素胶黏剂制备厚度15 mm刨花板的较佳工艺为施胶量12%,热压温度170℃,热压时间600 s,板坯表面不喷水。