Cotton Linters: An Alternative Cellulosic Raw Material

Summary: Cellulose in fibrous or in chemically modified form plays a relevant part in products for industrial applications and in products which are used in human daily life. Besides wood, cotton is an important natural source for cellulose. Linters are a by-product of the oil mills. The position of the linters in the technology of cotton is explained. In linters bleaching plant, the raw linters are purified mechanically and chemically. The principle of this process is shown. The resulting bleached linters (cotton linters pulp, CLP/cotton linters cellulose, CLC) have an alpha-cellulose content of about 99%. Due to their purity and to their properties, the cotton linters pulp is the cellulosic basis for a large number of special and niche products in the paper and chemical industry.     

Changes in cellulose structure during dissolution in LiCl:N,N-dimethylacetamide and in the alkaline iron tartrate system EWNN

The influence of different solvents on the morphology of cellulose during the dissolution process was studied. Spruce sulfite pulp, cotton linters and hydrolysed cotton linters were treated for a short time with lithium chloride: N,N-dimethylacetamide (LiCl:DMAc) and an alkaline solution of iron sodium tartrate (EWNN), respectively. The changes occurring at the fibre surfaces and within the cell walls were observed by scanning as well as by transmission electron microscopy. The cellulose fibres show significant differences in the dissolution behaviour when comparing the reaction of the two solvents. Using LiCl:DMAc, the cotton linters fibres become lamellar separated and within the spruce sulfite pulp fibres solvent channels appear in the first step with the fibrils becoming separated. In contrast, EWNN has a swelling effect on the surface of the cellulose fibres. Both solvent systems predominantly affect the ends of the fibres and places where the wall structure has been damaged.     

13C CPMAS NMR investigations of cellulose polymorphs in different pulps

In order to obtain information about the crystallinity and polymorphs of cellulose, and the occurrence of hemicelluloses in pulp fibers, wood cellulose, bacterial cellulose, cotton linters, viscose, and celluloses in different pulps were investigated by solid state ¹³C CPMAS NMR spectroscopy. A mixed softwood kraft pulp and a dissolving-grade pulp were treated under strongly alkaline and acidic conditions and the effect on cellulose crystallinity was studied. The presence of different crystalline polymorphs of cellulose and the amounts of hemicelluloses are considered.     

2.3 Wood pulp manufacturing and quality characteristics

Cellulose acetate being important in the fiber and textile industries is usually prepared from high quality cellulose such as cotton linters and wood pulps with an alpha cellulose content of more than 95%. In this section, therefore, wood pulps and cotton linters appropriate for cellulose acetate production were discussed in their chemical and physical properties so as to use them judiciously as natural raw materials for cellulose acetate production.     

Characterization of cellulose by SEC-MALLS

Norway spruce (Picea abies) cellulose samplesdissolved in lithium chloride/N,N-dimethyl-acetamide(LiCl/DMAc) covering a wide range of average molecular weights were analyzed bysize exclusion chromatography (SEC) and multi-angle laser light detection(MALLS). The molecular weight distribution of the samples was compared to themolecular weight distribution of cotton linters cellulose samples. To obtaincomplete dissolution of high-molecular-weight wood cellulose, previouslypublished procedures for dissolving cellulose in LiCl/DMAc were modified. SECseparation was performed using macroporous monodisperse polymer particles ascolumn matrix. The refractive index increment (dn/dc) forcellulose in 0.5% LiCl/DMAc was found to be 0.104. The radius of gyration,R_G, of cellulose in 0.5% LiCl/DMAc depended on the molecular weight,M, according to the relation R_G M^0.55. Celluloseprepared from sprucewood by the sulfite cooking process had a broad molecularweight distribution compared to cotton linters cellulose.     

Prehump in the gel-permeation chromatography fractionation of pulp cellulose acetate

GPC chromatograms of cellulose acetate made from wood pulp customarily show a shoulder or small separate peak at the high end of the DP distribution. Material isolated from this “prehump” area is considerably enriched in mannose and xylose, and the size of the prehump in acetates from different pulps correlates with the amount of hemicellulose in the pulp. Prehump is not ordinarily found in cellulose acetate made from linters but was induced by adding mannan at the start of the acetylation, or by prolonging the acetylation beyond the time when the cellulose acetate sulfate triester is first formed. Products of poor solubility, as indicated by increased haze and false viscosity, resulted in both cases. Prehump was reduced in pulp cellulose acetate by many of the steps which give products of improved solubility: mercerization of cellulose prior to acetylation, use of more sulfuric acid catalyst, replacement of part of the acetic acid with methylene chloride during acetylation, and by removal of a small amount of high viscosity or poorly soluble material by fractional precipitation.     

共溶剂存在下N-烯丙基吡啶氯盐离子液体对纤维素的溶解性能研究

采用一步法合成N-烯丙基吡啶氯盐离子液体([APy]Cl),考察其对纤维素的溶解性能.结果发现,在120℃下对棉浆粕(聚合度(DP)=556)的溶解度可高达19.71%,但再生后聚合度为223,热降解严重.通过添加不同种类共溶剂的方法克服此缺点.结果表明,有机溶液(DMSO,DMAc,DMF或吡啶)作为[APy]Cl的共溶剂时,[APy]Cl/DMAc复合溶剂对棉浆粕的溶解效果最佳,100℃下溶解度为15.03%,再生后聚合度为403.此外降低了溶剂成本.但70℃下,溶解度仅为1.36%,溶解能力较弱.继续探讨了[AMIM]Cl作为[APy]Cl的共溶剂时对纤维素的溶解性能,结果表明,70℃下,[APy]Cl/[AMIM]Cl复合溶剂对棉浆粕的溶解度为8.78%,再生后聚合度为516.可知添加上述2种共溶剂均使[APy]Cl在低于自身熔点下形成液体并能够溶解一定量纤维素,拓宽了溶解温度区间及应用平台.对FTIR,XRD和TGA谱图分析,结果表明上述为纤维素的直接溶剂,可将其晶型由Ⅰ型转变成Ⅱ型,再生后热稳定性稍有降低.通过照片和SEM表明再生膜无色透明,结构致密.     

Rheological properties of cellulose solution in paraformaldehyde/dimethyl sulfoxide system (1)

The rheological properties of three cellulose samples are investigated, including the dependence of the non‐Newtonian Index, structural viscosity and zero shear viscosity on temperature and the concentration of their paraformaldehyde/dimethyl sulfoxide solutions; the values of viscous flow activation energy of them are higher than that of the viscose solution. With the increase of molecular weight, solution concentration and the decrease of temperature, the rheological properties become worse. The rheological properties of cotton linters Cotton 1 are better than those of wood pulp Wood 2 despite a similar degree of polymerization. Copyright © 1999 John Wiley & Sons, Ltd.     

Structure of cellulose and microcrystalline cellulose from various wood species, cotton and flax studied by X-ray scattering

The structure of microcrystalline cellulose (MCC) made by mild acid hydrolysis from cotton linter, flax fibres and sulphite or kraft cooked wood pulp was studied and compared with the structure of the starting materials. Crystallinities and the length and the width of the cellulose crystallites were determined by wide-angle X-ray scattering and the packing and the cross-sectional shape of the microfibrils were determined by small-angle X-ray scattering. The morphological differences were studied by scanning electron microscopy. A model for the changes in microfibrillar structure between native materials, pulp and MCC samples was proposed. The results indicated that from softwood or hardwood pulp, flax cellulose and cotton linter MCC with very similar nanostructures were obtained with small changes in reaction conditions. The crystallinity of MCC samples was 54–65%. The width and the length of the cellulose crystallites increased when MCC was made. For example, between cotton and cotton MCC the width increased from 7.1 nm to 8.8 nm and the length increased from 17.7 nm to 30.4 nm. However, the longest crystallites were found in native spruce wood (35–36 nm).     

New solvents for cellulose: dimethyl sulfoxide/ammonium fluorides

New solvents based on DMSO in combination with alkylammonium fluorides, in particular TBAF . 3H(2)O and BTMAF . H(2)O, were established as media for homogeneous functionalization of cellulose. Even DMSO in combination with freshly prepared, anhydrous TBAF, obtained by the reaction of tetrabutylammonium cyanide and hexafluorobenzene, dissolves cellulose. In contrast, a mixture of DMSO and tetramethylammonium fluoride does not dissolve cellulose. The solvents were characterized by capillary viscosity, which showed that a cellulose solution of DMSO/BTMAF . H(2)O possesses a lower viscosity at comparable cellulose concentrations compared with DMSO/TBAF . 3H(2)O. The determination of the degree of polymerization of the starting cellulose (microcrystalline cellulose, spruce sulfite pulp, and cotton linters), and of the regenerated samples, shows that degradation of the polymer depends on the dissolution time, temperature and on the ammonium fluoride used. The results of different homogeneous reactions including acylation and carbanilation of cellulose in the solvents were compared with those of the most-commonly-applied solvent N,N-dimethylacetamide/LiCl. The products were characterized by elemental analysis, (1)H- and (13)C NMR spectroscopy (additionally after perpropionylation) and FTIR spectroscopy.     

Preparation of cellulose and cellulose derivative azo compounds

Wood pulp and cotton linter are the most common sources of cellulose forindustrial use. Methyl cellulose (MC) and cellulose sulfate (CS) were preparedusing bleached wood pulp and cotton linter. Coloured azo compounds were alsoprepared from coupling cellulose, wood pulp, MC and CS with aromatic diazoniumsalt. The presence of electron-releasing or withdrawing substituents affectedthe electrophilic substitution reaction. The produced azo compounds werecharacterized by FT-IR methodology, as well as mass spectrometry, in which thefunctional groups and the ion fragments of the products were analyzed.     

二醋酸纤维素-离子液体膜固定肌红蛋白制备过氧化氢传感器

将二醋酸纤维素(CDA)-(1-丁基-3-甲基咪唑四氟硼酸盐离子液体)([bmim]BF4)-肌红蛋白(Mb)的复合物修饰在玻碳电极(GCE)表面,制备了一种新型Mb修饰电极(CDA-[bmim]BF4-Mb/GCE).光谱分析表明:固定在CDA- [bmim]BF4-Mb膜中的肌红蛋白保持了其天然构象和生物活性.离子...     

A multivariate characterization of crystal transformations of cellulose

A spectroscopic study of cellulose transformation processes, such as alkali treatment and annealing, showed that, in combination with multivariate data analysis techniques, a detailed understanding of the crystalline transformation processes could be reached.¹³C cross-polarization magic-angle spinning (CPMAS) NMR and near-infrared (NIR) spectroscopy of cotton linters and softwood pulps analysed during the processing revealed information, after data reduction using principal components data analysis, that could be connected to structural changes of the cellulose polymorphs. The data showed that alkali treatment of cotton linters led to a cellulose conversion from cellulose I to II, while annealing, both for linters and pulps, yielded a transformation from I to I.     

Bottlebrush‐shaped copolymers with cellulose diacetate backbone by a combination of ring opening polymerization and ATRP

Graft copolymers with cellulose diacetate (CDA) backbone and both the poly(ε‐caprolactone) and polystyrene, or poly(butyl acrylate) or PMMA grafts were prepared by two‐step process. First, ε‐caprolactone (CL) was polymerized by ring‐opening polymerization (ROP) initiated with CDA, partly funcionalized with 2‐bromo‐isobutyryl groups (degree of functionalization was 0.5). The p(CDA‐g‐CL) copolymers were used in the second step as polyfunctional macroinitiators of ATRP of the vinyl monomer, giving densely grafted copolymers with polyester and PSt, or PBuA, or PMMA grafts. The prepared copolymers were characterized by SEC, some of them also by FTIR spectroscopy and atomic force microscopy (AFM). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 564–573, 2008     

Formation of free radicals in photoirradiated cellulose and related compounds

Free-radical formation in various modifications of celluloses, namely, wood cellulose I, II, III, and IV, rayon cellulose, amorphous cellulose, cotton linters, and absorbent cotton, irradiated with ultraviolet light, has been studied by means of ESR spectroscopy at 77°K. Various types of free radicals were generated from these samples. The line shapes and the signal intensities of the ESR spectra depended greatly upon the degree of crystallinity, the lattice type, and the arrangement of molecules in cellulose. The effect of degree of crystallinity and the amount of sensitizer (Fe³⁺) absorbed revealed that photochemical reactions in cellulose occurred exclusively in the amorphous regions of the polymer. Free radicals formed in these samples behaved distinctively upon a warm-up process. Phenomena of radical migration and formation of new radicals were observed from the sensitized samples of rayon cellulose and amorphous cellulose.     

Electron paramagnetic resonance spectroscopy of γ-irradiated cellulose and related compounds

EPR studies were carried out on different irradiated cellulosic materials. The shape of the EPR spectrum was found to depend upon the fine structure of cellulose. The peak-to-peak distances of the large peaks on the differential curves were found to be 23.3 and 24.8 gauss, respectively, for the amorphous and recrystallized cellulose. The number of free radicals present per unit weight in the recrystallized cellulose and in the amorphous cellulose were found to be in the ratio of 2.1:1. The EPR spectrum of a sample of irradiated cotton crystallites which was soaked in acetone before being dried was markedly symmetrical, in contrast to the EPR spectra of samples of cotton linters and of cotton crystallites dried from water, and was considered to be a reflection of the lower intermolecular bonding in the former. For corresponding doses, the free radicals on cotton crystallites have the highest g value, followed by cotton linters, followed by regenerated cellulose I. The g value decreased as the irradiation dose was increased.     

二醋酸纤维素 -聚乙二醇接枝共聚物的核磁共振表征

用^1H NMR和^13C NMR核磁共振技术研究了二醋酸纤维素和聚乙二醇的接枝反应,并确定了^1H NMR和^13C NMR谱中各谱峰的归属,为证明二醋酸纤维素和聚乙二醇的接枝反应提供了依据。     

Tunable mixed amorphous–crystalline cellulose substrates (MACS) for dynamic degradation studies by atomic force microscopy in liquid environments

Atomic force microscopy in liquid environments (L-AFM) became a state of the art technique in the field of enzymatic cellulose degradation due to its capability of in situ investigations on enzymatic relevant scales. Current investigations are however limited to few substrates like valonia cellulose, cotton linters and processed amorphous cellulose as only these show required flatness and purity. Structurally monophasic, these substrates confine conclusions regarding enzymatic degradation of mixed amorphous–crystalline substrates as commonly found in nature. To exploit the full potential of the technique, cellulose substrates with multiphase properties, flat topology and purity are therefore absolutely required. In this study we introduce a special preparation route based on highly crystalline Avicel PH101^® cellulose and the ionic liquid 1-butyl-3-methylimmidazolium chloride as dissolution reagent. As comprehensively shown by atomic force microscopy, wide angle X-ray scattering, Raman spectroscopy and electron microscopy, the developed material allows precise control of its polymorphic composition by means of cellulose types I and II embedded in an amorphous matrix. Together with the tunable composition and flat topology over large areas (>10 × 10 µm²) the material is highly suited for L-AFM studies.     

二醋酸纤维素接枝聚己内酯的核磁共振表征

用^1H-NMR和^13C-NMR研究了二醋酸纤维素(CDA)和聚己内酯(PCL)的接枝共聚反应,确定了^1H-NMR和^13C-NMR谱中各谱峰的归属,为证明二醋酸纤维素和己内酯的接枝共聚反应提供了依据。     

Cellulose liquefaction in acidified ethylene glycol

Wood pulp cellulose was used in a study of its catalyzed liquefaction in the presence of ethylene glycol, p-toluene sulfonic acid monohydrate or sulphuric acid being the catalysts. For this study, microcrystalline cellulose, Whatman filter paper no. 1 and cotton linters with molar masses of 76,000, 699,000 and 1,910,000 g mol⁻¹, respectively were used. This liquefaction was studied by gravimetric determinations, by X-ray diffraction analysis of the residual cellulose and by monitoring of the molar mass decrease over different time intervals, using size-exclusion chromatography. The disordered regions, even of cellulose with the highest molar mass degraded in the initial minute of liquefaction. However, the highly ordered cellulose regions remained relatively stable for a longer time. None the less, partial degradation of the highly ordered regions of the cellulose was achieved.