Molecular Weight of Lignin Fractions Leached from Unbleached Kraft Pulp Fibers

The molecular weights of lignin fractions leached from an unbleached kraft pulp were found to increase from 230,000 to 410,000 as washing of the pulp proceeded. The free diffusion coefficients for both a spherical and a disk-like conformation were calculated and were found to be seven orders of magnitude higher than the observed intrafiber diffusion coefficient. Also the change in the free diffusion coefficient with molecular weight was far less than the 100-fold polydispersity observed previously. A comparison of the molecular dimensions with the pore size indicated that a flat, disk-like conformation, rather than a spherical conformation, is appropriate for the lignin macromolecule.     

Light-Induced Yellowing of Mechanical and Ultrahigh Yield Pulps. Part 2. Radical-Induced Cleavage of Etherified Guaiacylglycerol-β-Arylether Groups is the Main Degradative Pathway

Bleached softwood mechanical pulp was treated with sodium borohydride to reduce carbonyl groups and dimethyl sulphate to block phenolic hydroxyl groups. Upon irradiation with near ultra-violet light, new phenolic hydroxyl groups and aromatic carbonyl groups formed. Existing mechanisms for photoyellowing require that either aromatic ketones or phenolic hydroxyls be initially present in the pulp, and cannot explain these observations. We interpret our results in terms of light-induced breakdown of etherified arylglycerol-β-arylether structures in lignin. Degradation occurs via the corresponding ketyl radicals, which cleave rapidly at the β-O-4 bond to give a phenoxy radical and an acetophenone enol. The enol tautomerizes to a ketone, while the phenoxy radical is oxidized to coloured groups. We believe that the ketyl route is the main lignin degradative pathway, and estimate that up to 70% of the colour formed during light-induced yellowing is attributable to this reaction.     

Studies on Mechanical Properties of Imide-Amine Cured Expoxy-Glass Fiber Laminates

Epoxy (DGEBA)-glass fiber laminates were cured with different hardeners. Imide-amine hardeners were synthesized with different chemical groups in their backbone structure. Higher curing and postcuring temperatures were required for epoxy-glass fiber laminates cured with imide-amine hardeners. Compared to epoxy cured with aromatic amine (DADPM), tensile and flexural strength increased by 38.5% and 23.1%, respectively, in the laminates cured with imide-amine with sulfone groups in the backbone structure. Fracture surface of the laminates showed good bonding between the fiber and matrix.     

The Topochemistry of Delignification Shown by Pulping Middle Lamella and Secondary Wall Tissue from Black Spruce Wood

Fractions of tissue from the secondary wall and middle lamella of black spruce wood were pulped by the kraft, acid-sulphite and acid-chlorite methods. In all cases, the delignification of the secondary wall tissue was more rapid than that for the middle lamella tissue. This topochemical effect was largest in kraft pulping. In acid-sulphite pulping the effect was less than in kraft, while in acid-chlorite pulping the effect was smallest. Thus the results confirmed in general the previously reported trends based on microscopic observation. However, in earlier work there was no topochemical difference found in acid-chlorite pulping, even at high delignification. In the present work, the topochemical effect in acid-chlorite pulping increased rapidly above 50% delignification.     

Structural and Molecular Properties of Residual Birch Kraft Lignins

The residual lignins from unbleached and oxygen-bleached birch kraft pulps were isolated by acid hydrolysis and characterized by elemental analysis, methoxyl content, permanganate degradation, size exclusion chromatography and quantitative 13-C NMR. Calculations based on the reduction in kappa number after the acid hydrolysis revealed that only about one third or less of the material assumed to be lignin could be isolated as polymeric lignin. This was shown to be a syringyl-guajacyl type of lignin with a syringyl-to-guaiacyl ratio of approximately 1:1. The rest of the material found in the acid solution after hydrolysis and identified by GC-MS and by pyrolysis-GC-MS was to a large extent low molecular weight furanoid structures probably originating from polysaccharide degradation products, with only traces of lignin-derived compounds present.     

The Influence of Oxygen on the Nitrogen Corona Treatment of Polyolefins

The resultant surface activation of polymers by corona discharges has been found to be markedly influenced by the type and purity of gases used in the corona. In this work it is shown that for the nitrogen gas corona treatment (15 KV, 15 mins) of polyethylene and polypropylene, traces of oxygen, >0.5% and <0.15% respectively, are sufficient to produce chemical changes in the polymer surface.     

造纸法烟草薄片打浆工艺和助留助滤剂的研究

首先对国内外烟草薄片成品的性能差异进行了分析比较,针对国内造纸法烟草薄片存在的质量问题,采用KRK磨浆机,进行烟草浆不同磨浆浓度条件下（4%、8%、18%、30%）的磨浆实验,并将由烟梗和碎烟制备的烟草浆与木浆配抄烟草基片,考察了磨浆浓度、添加不同助留助滤剂对烟草基片松厚度、干/湿抗张强度以及配抄浆料留着和滤水性的影响。结果表明：采用低浓（4%）磨浆、添加适量（0.6%左右）的壳聚糖抄造,所得烟草基片的综合质量较好,配抄浆料的留着和滤水性能好。     

纤维素酶预处理对化机浆磨浆及纤维形态的影响

研究了在精磨前用纤维素酶预处理杨木化学机械浆对磨浆的影响,探讨了纤维素酶用量对能耗、纸浆物理性能和纤维形态的影响,并采用扫描电镜和原子力显微镜对其表面形态进行分析。结果表明,随着酶用量的增加,磨浆能耗逐渐降低,但是纸浆的物理强度性能都有不同程度的降低。通过原子力显微镜和扫描电镜观察发现,酶处理后,纤维在打浆过程中容易分丝帚化和断裂,纤维长度下降,这也是纸浆物理强度性能降低的原因。     

现代造纸机的节能与降耗

讨论了装备控制先进、车速在准高速以上的现代造纸机实现节能降耗的几个途径,即改进各操作单元的结构、实施先进的关键技术与装备及提高其抄造率和产品成品率来提高整机效率。详细介绍了现代造纸机各操作单元的先进关键技术,以及这些关键技术对节能降耗的作用。通过分析现代造纸机在技术上仍存在的科技难题及我国的实际情况,提出研发国产现代造纸机的车速及幅宽的定位,并对我国研发及生产现代造纸机装备方面提出了合理的建议。