造纸专业英语6.ppt

1、,Reading material: wet-chemistry theory,Wet strength of paper is often referred to as relative wet-strength, the ratio between wet strength and dry strength. Normally, 10 to 15% is considered as a wet-strength paper. In contrast to dry strength, the origins in the hydrogen bonds present in natural c

2、ellulose, wet strength requires water stable (covalent) bonds. Naturally, cellulose contains few covalent bonds, and therefore wet-strength chemicals are necessary.,hydrogen bond 氢键 covalent bond 共价键 -valent .价的 co- 共同，一起,Reading material: wet-chemistry theory,Polymer resins are often used to increa

3、se wet strength. Two different wet-strength mechanisms exist, the protection mechanism and the reinforcement mechanism. The protection mechanism involves diffusion of the wet-strength polymer to the fibre surface where it cross-links through and around the fibres. Such cross-linked networks prevent

4、fibre swelling and helps to preserve covalent bonds when the paper is exposed to water. In contrast, the reinforcement mechanism means that new bonds between the wet-strength polymer and the fibres are formed.,mechanism 机理 diffusion 扩散 cross-link 交联,Reading material: wet-chemistry theory,Fiber charg

5、e is an important factor that influences the papermaking process as well as the paper properties. Cellulose fibres contain various ionisable groups: carboxyl-, sulfonic acid-, phenolic- and hydroxyl groups and are therefore negatively charged at all pH values.,charge n. 电荷 v. 使充电 ionisable 可离子化的 gro

6、up 基团 carboxyl 羧基 sulfonic acid 磺酸 phenolic 酚的 hydroxyl 羟基,Reading material: wet-chemistry theory,Under normal papermaking conditions, the negative fibre charge is due to carboxyl and sulfonic acid groups. These charged groups are located either on the fiber surfaces or inside the cell wall; hence t

7、hey are referred to as surface- and bulk charges, respectively. Surface charges are important for fibre- and paper strength.,cell wall 细胞壁 bulk 大小, 体积, 大批, respective 分别的,Reading material: wet-chemistry theory,Adsorption of polymers is used in many applications. The driving force is a strong polymer

8、-surface interaction. If the solvent is poor, then adsorption is more favourable than the polymer-solvent interaction. A condition for most cationic additives is the ability to adsorb to the fibre surface. That is why polymer additives used in papermaking often are cationic.,adsorption n. 吸附 adsorbe

9、nt 吸附剂 absorbent 吸收剂 Solvent n. 溶剂 poor solvent 不良溶剂,Reading material: wet-chemistry theory,The density and distribution of charges are also very important. Other factors that affect the adsorption are molecular weight of the polymer and the presence of fibre segments called “fines”. Fines have larg

10、e specific area and their capacity to adsorb polymers is therefore higher than for whole fibres.,density n. 密度 distribution n. 分布 molecular weight 分子量 segment 片断 fine 细小纤维 specific area 比表面积 specific 比的,Reading material: wet-chemistry theory,Polymer adsorption is often reversible and there is a prob

11、ability that they will detach from the surface. This probability is generally low since all segments have to detach at the same time. However, changes in pH, ionic strength etc. might cause desorption of polymers from the fibre surface.,reversible adj. 可逆的 ionic strength 离子强度 desorption n. 解吸,Readin

12、g material: wet-chemistry theory,The natural biopolymer： A natural biopolymer is generally characterized in terms of its: quality (heavy metal/protein content, pyrogenicity, clarity etc), intrinsic properties (molecular weight, viscosity, degree of deacetylation, stability) and physical form (size e

13、tc).,biopolymer 生物聚合物 characterize 表现特色 in term of 依照 heavy metal 重金属 protein 蛋白质 content 含量 pyrogenicity 致热性 clarity 透明度 intrinsic property固有特性 viscosity 黏度 deacetylation 脱乙酰作用,Reading material: wet-chemistry theory,The commercial prospect of the actual biopolymer is good since its natural resource

14、s are abundant. The natural biopolymer has the following properties: availability and ability to be used in varying form: powder, solution and gels. Non-toxicity Biocompatibility Good absorption capacity Non-water solubility,gel 凝胶 Biocompatibility 生物适应性,Reading material: wet-chemistry theory,Its la

15、rgest use is as flocculent and chelator of toxic and radioactive metals but some other important applications can be cited: as a component in wound dressings and drug delivery systems thanks to its biocompatibility, non-toxicity and wound-healing effect. The natural biopolymer is also an excellent m

16、oisturizer and is therefore used in hair- and skin care products.,flocculent 絮凝剂 chelator 螯合剂 chelate 螯合物，使螯合 radioactive 放射性的 dressing 敷料 component 成分 moisturizer 润湿剂,Reading material: wet-chemistry theory,The actual biopolymer has, like cellulose, a linear structure but instead of the hydroxyl gro

17、up there is another reactive group. At acidic pH these groups become positively charged groups with high reactivity. Thus, they are very efficient in neutralizing the negatively charged fibres.,linear 线型的 reactive group 活性基团 reactivity neutralize 使中和,Reading material: wet-chemistry theory,The possib

18、ility of the natural biopolymer to be used as wet-strength additive lies within its structure, which is very similar to that of cellulose or CMC (carboxyl methylcellulose); the glucose units are linked together by -1,4 glycoside bonds. The close similarity to cellulose probably makes it possible for

19、 the natural biopolymer to form strong hydrogen bonds to cellulose. By studying the irreversible adsorption of CMC to cellulose some general wet-strength mechanisms can be understood.,carboxyl methylcellulose 羧甲基纤维素 glucose 葡萄糖 glycoside 葡萄糖甙, 甙, 配糖体,Reading material: wet-chemistry theory,Irreversib

20、le adsorption of CMC： CMC is the most widely used water-soluble derivate of cellulose. It is produced by reacting cellulose with monochloracetate.,derivate 衍生物 = derivative monochloracetate 一氯醋酸,Reading material: wet-chemistry theory,Irreversible adsorption of CMC is an alternative to improve paper

21、strength. CMC can be irreversibly attached to cellulose at high temperature and in presence of an electrolyte. A salt is used to shield the repulsion between negatively charged fibres and CMC, making it possible for CMC to approach the fibre surface and attach. The irreversible adsorption is believe

22、d to be a matter of co-crystalisation mechanisms. An irreversible adsorption is thermodynamically stable and cannot be washed away.,electrolyte 电解质 repulsion 排斥力 co-crystalisation 共结晶作用 thermodynamical 热力学的,Reading material: wet-chemistry theory,A common technique for wet-strength development of pap

23、er is to add CMC together with PAC to the pulp. Cationic PAE helps to retain the anionic CMC to the fibre surface. Both dry and wet strength are improved. The surface conformation and properties of such fibres will be different compared to when only CMC is added.,polyaluminum chlorides 聚合氯化铝 PAC pol

24、yaminoamide - epichlorohydrin聚酰胺多胺环氧氯丙烷(PAE) amino 氨基的 amide 酰胺 amine 胺 imine 亚胺 conformation 构造,Reading material: wet-chemistry theory,Temperature has strong effect on CMC adsorption. The adsorption increases rapidly with temperature up to 120C. High electrolyte concentration also promotes the adso

25、rption. At low electrolyte concentration no CMC is attached between pH6 and 11 whereas high electrolyte concentration makes the adsorption less pH dependent. Acidic conditions are more favourable and the adsorption increases when a divalent-instead of a monovalent ion is used.,C Dcgrees Centigrade 摄氏度 Fahrenheit 华氏 dival