Effect of Kraft Cooking Conditions on the Chemical Composition of the Surface and Bulk of Spruce Fibers

By varying cooking temperature, alkali charge, ionic strength, and cooking time in Kraft pulping of spruce chips, pulps ranging between kappa numbers 20–80 were obtained. The unbleached Kraft pulp fibers were subjected to mechanical peeling in order to separate the surface material from the bulk of the fibers and the carbohydrate composition and lignin content of the two fractions were analyzed. As expected, the lignin and xylan contents were higher on the fiber surface than in the fiber wall. The percentage of xylan on the fiber surface was fairly constant, independent of different pulping conditions or degree of delignification. The lignin proportion on the fiber surface gradually decreased with decreasing kappa number. At a given kappa number, pulping at a higher temperature resulted in less lignin on the fiber surface, probably because of the higher solubility of lignin at higher temperature. Cooking at lower alkali charge also resulted in lower lignin content on the fiber surface at a given kappa number. In this case, there was more time available for degradation of the surface lignin since the lower alkali charge resulted in longer cooking time needed to reach a certain kappa number.     

麦草蒸汽爆破处理的研究──Ⅱ.麦草蒸汽爆破处理作用机制分析

对汽爆麦草进行了电镜观察及差热、红外光谱和纤维表面特征的X-射线光电子能港分析（XPS）。汽爆麦草显微形态表明,在汽爆过程中木质素部分被抽提出之后,又重新分布沉聚于纤维的表面。汽爆麦草的差热性质分析说明了汽爆使麦草的半纤维素和部分木质素降解为低分子物质,并且使纤维疏松,形成多孔性,易于燃烧。汽爆麦草红外光谱分析表明,添加了碱性物质,半纤维素降解得很少。因此,汽相蒸煮的酸碱度是半纤维素溶出的的关键性因素。汽爆麦草纤维表面特征的XPS分析结果也说明汽馒处理使纤维比表面积增加,余水性基团更多。     

One‐step green treatment of hemp fiber used in polypropylene composites

In this article, an eco‐friendly and cost effective surface treatment method is proposed for hemp fiber, enabling fabrication of hemp fiber/polypropylene (PP) composites, which show better mechanical properties than the PP composites containing untreated or alkali treated hemp fiber. Various techniques, such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), moisture analysis, and differential scanning calorimetry (DSC), are employed for the characterization of hemp fiber and polymer composites interface. Based on these results, the conventional alkali treatment of hemp fiber results in the damage of elementary fiber by eliminating parts of lignin and hemicellulose, which could be the reason for the decline of mechanical properties for the resulted polymer composites. On the contrary, water treatment cleans the fiber surface by effectively removing the water‐soluble polysaccharides while ensures minimum degradation on elementary fiber structure, which contributes to the improved mechanical properties of final polymer composites: the Young's modulus, fracture stress and fracture strain were enhanced by 3.66, 7.86, and 14.6%, respectively, when compared with untreated fiber reinforced composites. POLYM. COMPOS., 37:385–390, 2016. © 2014 Society of Plastics Engineers     

不同预处理对剑麻纤维组分和结构的影响

采用机械破碎、酸法蒸煮、氢氧化钠溶液碱法蒸煮、氨水处理和蒸汽爆破等五种不同物理和化学方法对剑麻纤维进行处理。通过化学分析、扫描电镜(SEM)及红外光谱(IR)等手段表征了处理前后剑麻纤维组分和结构的变化。结果表明,不同预处理方法均使剑麻纤维组分分离,杂质含量降低,纤维素含量提高。其表面形态和聚集态结构根据不同的处理方法而发生不同变化。在五种方法中以碱煮和蒸汽爆破处理效果较佳。     

Characterization of an alkali‐treated grass fiber by thermogravimetric and X‐ray crystallographic analysis

The thermal behavior of grass fiber was characterized by means of thermogravimetric analysis and differential scanning calorimetry analysis. The results proved that the removal of water‐soluble matter improved the thermal behavior of grass fiber over that of unleached fiber, and this was further enhanced by an alkali treatment of the grass fiber. The isothermal weight loss of the grass‐fiber specimens was analyzed at 100, 200, and 300°C for different time periods. Accelerated aging of the grass‐fiber samples was carried out to determine the effect of aging on the tensile strength. Partially delignified grass fiber showed maximum thermal stability. X‐ray diffraction analysis was also performed to verify the composition and to correlate the change in the tensile strength due to the water leaching and alkali treatment. The processing of grass fiber with NaOH and NaClO₂ reduced the amorphous fraction in the fiber sample. This may have been a result of the loss of the amorphous noncellulosic components of the fibers and the degradation of the unordered regions of the grass fiber. However, mercerization of the grass fiber revealed an increase in the amorphous fraction after a certain time exposure, confirming the decrease in the crystallinity. The morphology of the water‐leached and alkali‐treated grass fiber was studied with scanning electron microscopy © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of fiber surface treatment on the properties of biocomposites from nonwoven industrial hemp fiber mats and unsaturated polyester resin

Biocomposites were made with nonwoven hemp mats and unsaturated polyester resin (UPE). The hemp fiber volume fraction was optimized by mechanical testing. The effect of four surface treatments of industrial hemp fibers on mechanical and thermal properties of biocomposites was studied. The treatments done were alkali treatment, silane treatment, UPE (matrix) treatment, and acrylonitrile treatment. Bending strength, modulus of elasticity, tensile strength, tensile modulus, impact strength, storage modulus, loss modulus, and tan δ were evaluated and compared for all composites. The mechanical as well as thermal properties of the biocomposites improved after surface treatments. The properties of the above biocomposites were also compared with E‐glass–mat composite. To achieve balance in properties, a hybrid composite of industrial hemp and glass fibers was made. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1055–1068, 2006     

Influence of alkali fiber treatment and fiber processing on the mechanical properties of hemp/epoxy composites

Industrial hemp fibers were treated with a 5 wt % NaOH, 2 wt % Na₂SO₃ solution at 120°C for 60 min to remove noncellulosic fiber components. Analysis of fibers by lignin analysis, scanning electron microscopy (SEM), zeta potential, Fourier transform infrared (FTIR) spectroscopy, wide angle X‐ray diffraction (WAXRD) and differential thermal/thermogravimetric analysis (DTA/TGA), supported that alkali treatment had (i) removed lignin, (ii) separated fibers from their fiber bundles, (iii) exposed cellulose hydroxyl groups, (iv) made the fiber surface cleaner, and (v) enhanced thermal stability of the fibers by increasing cellulose crystallinity through better packing of cellulose chains. Untreated and alkali treated short (random and aligned) and long (aligned) hemp fiber/epoxy composites were produced with fiber contents between 40 and 65 wt %. Although alkali treatment generally improved composite strength, better strength at high fiber contents for long fiber composites was achieved with untreated fiber, which appeared to be due to less fiber/fiber contact between alkali treated fibers. Composites with 65 wt % untreated, long aligned fiber were the strongest with a tensile strength (TS) of 165 MPa, Young's modulus (YM) of 17 GPa, flexural strength of 180 MPa, flexural modulus of 9 GPa, impact energy (IE) of 14.5 kJ/m², and fracture toughness (K_Ic) of 5 MPa m^1/2. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

不饱和聚酯树脂/大麻纤维复合材料性能的研究

采用模压工艺制备了不饱和聚酯(UP)树脂/大麻纤维复合材料,研究了大麻纤维加入量及纤维的碱处理、乙酰化处理及偶联剂处理对复合材料力学性能的影响;采用傅立叶变换红外光谱仪对复合材料的结构进行了表征和分析。结果表明,随着大麻纤维含量的增加,UP树脂/大麻纤维复合材料的拉伸弹性模量逐渐增加,拉伸强度、弯曲强度、弯曲弹性模量及冲击强度等均先降低而后逐渐增大;偶联剂处理对复合材料力学性能的改善效果最好;偶联剂与纤维之间发生了酯化反应。     

Evaluating the thermal stability of high performance fibers by TGA

The thermal degradation of eight types of high performance fibers (HPFs) was measured under nitrogen and air atmosphere. The degree of degradation, as measured by weight loss using thermogravimetric analysis (TGA), and the characteristic degradation temperatures were obtained. The kinetics of the thermal degradation has also been analyzed according to the Freeman–carroll method and the activation energies of the HPFs were estimated. The experimental results show that para‐aramids (Kevlar® 29, 49, 129, and Twaron®2000) have similar thermal stability, but their thermal degradation temperatures and activation energies in air are different from those in nitrogen, which means that the thermostability of the fiber depends not only on its intrinsic structure but also on the atmosphere and temperature of testing environment. Terlon® fiber shows higher degradation temperature as a copolymer of para‐aramid, and its initial degradation temperature is 476.4°C in air. It can also be found that the PBO (poly(p‐phenylene benzobisoxazole)) fiber has the highest thermal degradation temperature among the samples tested, but its activation energy is not the highest in both air and nitrogen atmosphere. And the UHMW‐PE (ultra high molecular weight polyethylene) fiber has the lowest thermal degradation temperature, and it begins to degrade when the temperature reaches 321.8°C under air atmosphere. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 937–944, 2006     

Structure and properties of hemp fabric treated with chitosan and dyed with mixed epoxy‐modified silicone oil

To enhance the color yield and improve the soft handle, hemp fabrics were treated with chitosan of molecular weight 4200 and degree of deacetylation 0.90, and then dyed using Remazol Brillant Blue R with mixed epoxy‐modified silicone oil in different volume ratios. The structural changes in hemp fibers were investigated by means of scanning electron microscope, FTIR, TG, DSC, and XRD. The properties of tensile, bending, dyeing, and color fastness for hemp fabric were also studied. The results showed that when compared with the untreated hemp fiber, the thermal performance of chitosan/silicone oil‐modified hemp fiber changed and the percent residual weight increased in the range of temperature 25–550°C. The crystal grain size decreased and the degree of crystallization increased. For chitosan/silicone oil‐treated hemp fabric, the flexural stiffness and tensile properties degraded. The maximum color yield (K/S value) was obtained when the volume ratio of dyeing liquor to silicone oil was 2 : 1. The color fastnesses to rubbing and wet scrubbing were also improved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Studies on Thermal Degradation of Cellulosic Fibers Treated with Flame Retardants

Hemp fabric, one of the most flammable materials, was treated with compounds containing different kinds of elements that contribute to flame retardation. For a study of flame retardation from the standpoint of thermal degradation, the samples were subjected to thermogravimetry (TG) and differential thermal analysis (DTA) in air from ambient temperature to 600℃. The apparent activation energy (Ea) is evaluated by Broido's method at different stages of thermal degradation to observe the variation of Ea in the process of thermal degradation. Flame retardation of samples was determined by limiting oxygen index (LOI) to find the effects of the different compounds on flammability and the thermal degradation of the hemp fabric. The composition of the chars was studied by the IR spectra to obtain information concerning the thermal degradation mechanism. Compared with flammable hemp, the hemp fabric treated with flame retardants showed a higher LOI but lower Ea and decomposition temperatures, which indicated that some compounds make the hemp fabric decompose at lower temperatures, resulting in less flammable products.     

Utilization of bowstring hemp fiber as a filler in natural rubber compounds

The cure characteristics and physicomechanical properties of natural rubber (standard Nigerian rubber) vulcanizates filled with the fiber of bowstring hemp (Sansevieria liberica) and carbon black were investigated. The results showed that the scorch and cure times decreased, whereas the maximum torques increased, with increasing filler loadings for both bowstring hemp fiber and carbon black filled vulcanizates. The tensile strength of both bowstring hemp fiber and carbon black filled vulcanizates increased to a maximum at a 40 phr filler concentration before decreasing. The elongation at break and rebound resilience decreased, whereas the modulus, specific gravity, abrasion resistance, and hardness increased, with increasing filler contents. The carbon black/natural rubber vulcanizates had higher tensile strength, which was about 1.5 times that of bowstring hemp fiber/natural rubber vulcanizates. This superiority in the tensile strength was probably due to the higher moisture content and larger particle size of the bowstring hemp fiber. However, the bowstring hemp fiber/natural rubber vulcanizates showed superior hardness. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Unidirectional hemp and flax EP‐ and PP‐composites: Influence of defined fiber treatments

In some technical areas, mainly in the automotive industry, glass fiber reinforced polymers are intended to be replaced by natural fiber reinforced polymer systems. Therefore, higher requirements will be imposed to the physical fiber properties, fiber‐matrix adhesion, and the quality assurance. To improve the properties of epoxy resins (EP) and polypropylene (PP) composites, flax and hemp fibers were modified by mercerization and MAH‐PP coupling agent was used for preparing the PP composites. The effects of different mercerization parameters such as concentration of alkali (NaOH), temperature, and duration time along with tensile stress applied to the fibers on the structure and properties of hemp fibers were studied and judged via the cellulose I–II lattice conversion. It was observed that the mechanical properties of the fibers can be controlled in a broad range by using appropriate mercerization parameters. Unidirectional EP composites were manufactured by the filament winding technique; at the PP matrix material, a combination with a film‐stacking technique was used. The influence of mercerization parameters on the properties of EP composites was studied with hemp yarn as an example. Different macromechanical effects are shown at hemp‐ and flax‐PP model composites with mercerized, MAH‐PP‐treated, or MAH‐PP‐treated mercerized yarns. The composites' properties were verified by tensile and flexural tests. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2150–2156, 2004     

Alkali resistance of a casein‐acrylonitrile graft copolymer fiber

The casein‐acrylonitrile graft copolymer fiber was treated in sodium hydroxide, sodium carbonate, and sodium bicarbonate solutions to evaluate its alkali resistance which was very important for wet processing. The weight loss and whiteness of the treated fibers were examined. UV spectra of the alkaline treatment solutions and IR spectra of the treated fibers were analyzed. The study showed that the fiber exhibited poor alkali resistance. Treating temperature, alkali concentration, and strength affected the weight loss and whiteness of the treated fibers. A high weight loss was found even at low alkali concentration, and the obvious yellowing was observed at higher alkali concentration and temperature. The weight loss was primarily due to the hydrolysis of casein, whereas the yellowing was caused by the hydrolysis of nitrile groups and induced formation of C?N conjugated system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

废PCB粉/PP复合材料的非等温热分解动力学

利用热重分析法(TGA)研究了聚丙烯(PP)、废印刷电路板非金属粉/聚丙烯(废PCB粉/PP)复合材料的热分解过程,分别采用Kissinger法和Flynn-Wall-Ozawa法研究了PP及其复合材料的热分解动力学。结果表明,废PCB粉的加入可明显提高复合材料的热稳定性。当废PCB粉用量升高到50%时,最大热分解速率温度(472.7℃)与纯PP(451.4℃)相比提高了21.3℃。废PCB粉中的玻璃纤维与PP分子链相互缠结,限制了聚合物分子的运动,使废PCB粉/PP复合材料的活化能与聚丙烯相比明显增大,复合材料分解需要更高的温度,且随废PCB粉用量的增加,复合材料的活化能不断增加,当废PCB粉用量为50%时,复合材料活化能与聚丙烯相比约提高了44.8%。     

Effect of fiber content and type,compatibilizer, and heating rate on thermogravimetric properties of natural fiber high density polyethylene composites

Natural fiber polyethylene composites containing kenaf fibers, wood flour, newsprint, and rice hulls at 25 and 50% (by weight) fiber content were sampled and studied using thermogravimetric analysis (TGA). The effects of fiber type and content, compatibilizer and heating rate on the thermal stability and degradation of the composites were evaluated. Among different natural fibers, kenef fibers were found to be the least thermally stable ones whereas newsprint fibers proved to be the most stable fibers in composite formulations. Composites containing higher amounts of natural fiber degraded at a higher rate and exhibited higher weight loss. The presence of the compatibilizer resulted in composites with slower thermal degradation. Heating rate increased both temperature and rate of main degradation peaks. FTIR and DSC results are also presented to discuss phenomena leading to thermal degradation. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.     

Effect of chemical modifications on the thermal stability and degradation of banana fiber and banana fiber‐reinforced phenol formaldehyde composites

Banana fiber has been modified by treatments with sodium hydroxide, silanes, cyanoethylation, heat treatment, and latex treatment and the thermal degradation behavior of the fiber was analyzed by thermogravimetry and derivative thermogravimetry analysis. Both treated and untreated fibers showed two‐stage decomposition. All the treatments were found to increase the thermal stability of the fiber due to the physical and chemical changes induced by the treatments. The thermal degradation of treated and untreated banana fiber‐reinforced phenol formaldehyde composites has also been analyzed. It was found that the thermal stability of the composites was much higher than that of fibers but they are less stable compared to neat PF resin matrix. Composite samples were found to have four‐stage degradation. The NaOH treated fiber‐reinforced composites have very good fiber/matrix adhesion and hence improvement in thermal stability is observed. Though both silane treatments increased the thermal stability of the composite the vinyl silane is found to be more effective. Heat treatment improves the crystallinity of the fiber and decreases the moisture content, hence an improved thermal stability. The latex treatment and cyanoethylation make the fiber surface hydrophobic, here also the composite is thermally more stable than untreated one. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Influence of optimal alkali treated Areca catechu L. peduncle fiber for light weight polymer composites applications

The chemical, physico-mechanical, morphological, and thermal characteristics of alkali treated natural cellulosic sustainable eco-friendly fiber from peduncle of Areca Catechu tree were investigated. Areca Catechu fruit peduncle fiber (ACFPF) treated with 5% (w/v) NaOH solution for 60 min is found as optimally alkali treated ACFPF (OAACFPF) witnessed an increase in cellulose content by 17%. Single fiber tensile test perceived that OAACFPF enhanced tensile strength by 12.9% and x-ray diffraction analysis depicts crystallinity index of OAACFPF improved by 14.2% compared with ACFPF. Also, Fourier transform infrared spectroscopy analysis endorsed partial removal of amorphous contents from fibers due to alkali treatment. In addition, alkali treatment has enhanced thermal stability of OAACFPF from 226°C to 235°C verified through Thermogravimetric analysis. Likewise, Differential scanning calorimetry analysis confirmed improvement in thermal degradation temperature of OAACFPF after alkali treatment. Moreover, the rougher surface of OAACFPF confirmed through scanning electron microscope and atomic force microscopy is due to partial removal of amorphous contents thus ensuing in good interfacial bonding characteristics with the matrix during reinforcement for bio-composite fabrication. The above findings validated OAACFPF as a worthy substitute to harmful synthetic fibers for development of eco-friendly and sustainable bio-composites.     

海藻酸钙纤维的结构与性能

研究了自制的海藻酸钙纤维的结构、热性能、燃烧性能以及对酸、碱和盐溶液的化学稳定性能。结果表明:海藻酸钙纤维的微观形态和粘胶纤维的相似,红外光谱结果证实了海藻酸钙纤维中"egg-box"结构的存在;海藻酸钙纤维的化学稳定性较差,随着处理液浓度和温度的升高,以及处理时间的延长,其稳定性越差;海藻酸钙纤维的热稳定性较好,极限氧指数为34.4,具有很好的阻燃性,属于难燃纤维。     

Thermal degradation of a phenolic resin,vegetable fibers,and derived composites

The thermal degradation behavior of resol, several vegetable fibers (two types of cotton fibers, sisal and sugar cane bagasse) and derived polymer composites have been investigated using thermogravimetric analysis (TGA). The initial thermal degradation temperature T_ONSET, the temperature at the maximum degradation rate TD_M, and the char left at 500°C corresponding to the crosslinked resol were higher than the values measured for the fibers and their composites. Thus, the addition of the fibers reduced the thermal resistance of the phenolic thermoset. The polymer and the fiber‐composites showed a complex degradation involving different thermal decomposition processes. For that reason, the DTG curves were deconvoluted and a phenomenological kinetic expression was found for each individual peak. The overall thermal decomposition curve was recalculated adding each degradation process weighted according to its contribution to the total weight loss. An increase in the activation energy corresponding to the cellulose degradation was observed in the composites, highlighting the protective action of the resin encapsulating the fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008