亚麻分层纳米纤维素的制备及其增强热电复合材料性能

为从天然亚麻纤维中制备出分层纳米纤维素(即纤维素纳米纤维(CNF)与纤维素纳米晶(CNC)共存),并对其制备方法进行优化完善,提出将亚麻纤维在特定浓度的氢氧化钠溶液中碱化处理后,再进行四甲基哌啶氮氧化物(TEMPO)介导的三元氧化和机械处理的联合处理方法。然后将亚麻CNF与石墨烯复合制备CNF/石墨烯复合薄膜并研究亚麻CNF增强热电复合材料的性能。结果表明:碱化预处理使亚麻纤维直径变细,长度变短,半纤维素被脱除,是生成不同尺寸CNF的重要步骤;随着氢氧化钠用量在0~18%范围内的增加,所得CNF悬浮液的光透过率从3.7%增加到95.1%;CNF/石墨烯复合膜表现出最高功率因子,为8.0×10 ^-3 μW/(m·K ²),表明复合薄膜具有热电性能。     

Flax retting by degumming composite enzyme produced by Bacillus licheniformis HDYM-04 and effect on fiber properties

Flax enzymatic retting with composite enzyme produced by microbes with inexpensive substrates is widely researched due to less contamination and lower cost. Bacillus licheniformis HDYM-04, isolated from a liquid sample of flax retting pool, efficiently produced degumming enzymes after 48 h of fermentation with inexpensive konjaku flour, consisted of 587.5 U/mL pectinase, 365.2 U/mL mannanase, and 140.1 U/mL xylanase. Almost half the maximum activity of three above-mentioned degumming enzymes was maintained at pH 4.0–6.0 which demonstrated its stability in pH condition of flax retting. After 120 h of retting with this composite enzyme, scanning electronic microscopy showed more significant reduction in gummy components on the fiber surface than those of water retting. The fiber strength was 182.4 ± 9.3 N, 14.3% higher than water-retted samples. The long fiber rate and fiber yield also verified higher fiber productivity. The results permitted this degumming composite enzyme an applicable potential in flax retting.     

Progress in Enzyme-Retting of Flax

Abstract

New methods for retting flax are sought to overcome problems in the current method of dew-retting of flax. Published data are reviewed and new data presented on the development and testing of a method to ret flax using pectinase-rich enzyme mixtures plus chelators based on cost and fiber yield and properties. In spray enzyme retting (SER), flax stems are crimped to physically disrupt the plant's protective barrier and then sprayed until soaked with, or briefly immersed in, an enzyme/chelator formulation. Flax is then incubated at temperatures optimal for enzyme activity, washed, and dried. Pilot scale tests, conducted with 10 kg samples of flax retted with a series of formulations, showed that this method effectively retted flax stems from a variety of sources, including fiber flax, mature fiber flax, and linseed straw. Fiber yield, strength, and fineness were significantly influenced by variations in enzyme-chelator amounts. Cellulases inpectinase mixtures appeared to preferentially attack dislocations in fibers and fiber bundles resulting in loss of fiber strength. Polygalacturonases alone effectively separated fiber from non-fiber components. The SER method proved to be an effective framework for further tests on enzyme-chelator formulations that now must be integrated with physical processing to optimize the extraction of flax fibers based on cost and fiber yield and properties.     

Free vibration analysis of a composite reinforced with natural fibers employing finite element and experimental techniques

ABSTRACT

Composites have been extensively used in the modern era in wide range of applications. This article deals with the study of vibration characteristics of natural fiber reinforced composite beam in which Aloe vera fiber is reinforced in epoxy matrix and is used in combination with glass-epoxy. Finite element method of analysis is adopted using Ansys software. Effects of several parameters like laminate stacking sequence, support conditions, material hybridization, and number of layers, etc. on the natural frequency of natural fiber reinforced composite beam are analyzed. Experimental study on Aloe vera fiber reinforced composite beam is also conducted for validation.     

Drilling Behavior of Flax/Poly(Lactic Acid) Bio-Composite Laminates: An Experimental Investigation

ABSTRACT

This paper aims to investigate the effects of machining parameters such as spindle speed, feed rate and drill diameter on machinability of flax/poly(lactic acid) bio-composites, to analyze the relations among cutting forces, drilling-induced damages and crack propagation of the drilled samples. In particular, a set of drilling experiments were conducted using different drilling conditions and a new low-cost measurement set-up was developed to measure the cutting force during the drilling operation. In addition, the analysis of variance (ANOVA) was applied to identify the significance of each individual cutting parameter. The experimental results indicate the relation between the thrust force and the machinability parameters of flax fiber reinforced bio-composite. The increase in spindle speed reduces thrust force and delamination size of the drilled holes, whereas an increase in feed and drill diameter leads to a considerable increase in both thrust force and delamination factor. The effect of spindle speed on peripheral damage was not significant for the drills tested, though the feed rate was found to play the key role on the delamination damage area. The best hole quality was achieved with the samples drilled at spindle speed and feed rate of 3000 rpm and 0.11 mm/rev, respectively.     

Studies on Mechanical and Morphological Characterization of Developed Jute/Hemp/Flax Reinforced Hybrid Composites for Structural Applications

In the present study, an attempt has been made to develop and characterize natural fiber-based composites (jute/epoxy, hemp/epoxy, flax/epoxy) and their hybrid composites (jute/hemp/epoxy, hemp/flax/epoxy, and jute/hemp/flax/epoxy) using hand-lay-up technique. Mechanical characterization (tensile, flexural, impact, and hardness test) of the developed composites was performed. The interface between fiber and matrix was examined using scan electron microscopy (SEM). Among (jute/epoxy, hemp/epoxy, flax/epoxy), flax/epoxy composite has shown higher hardness (98 Shore-D) and tensile strength (46.2 MPa) whereas better flexural and impact strength have been shown by hemp/epoxy (85.59 MPa) and jute/epoxy (7.68 kJ/m²) composites respectively. Results showed that hybrid composites observed better mechanical properties. Jute/hemp/flax/epoxy hybrid composite showed the highest tensile strength, modulus and impact strength of 58.59 MPa, 1.88 GPa, and 10.19, kJ/m², respectively. Jute/hemp/epoxy hybrid composite achieved the maximum flexural strength of 86.6 MPa.     

亚麻纤维增强聚乳酸复合材料的制备与性能表征

针对预成型件的铺层角度对复合材料力学性能产生影响的问题,以亚麻纤维为增强体,与聚乳酸纤维通过开松、混合、梳理工序制成预成型件后,采用模压成型工艺制备了亚麻纤维/聚乳酸复合材料。研究预成型件的各种铺层角度对复合材料拉伸、弯曲性能的影响,并通过扫描电镜讨论亚麻/聚乳酸复合材料的破坏机制以及拉伸断裂形貌。结果表明：铺层角度为90°时,复合材料横向拉伸、弯曲强度和模量最高;铺层角度为0°时,复合材料纵向拉伸、弯曲强度和模量最高。     

Sound absorption properties of composite structure with activated carbon fiber felts

This paper is intended to study the influence of different factors on the sound absorption properties of composite structure with activated carbon fiber felts. Activated carbon fiber felts made from viscose fiber mats were prepared and later combined with perforated panels to form four different composite sound absorption structures. Based on the transfer function method, the impedance tube was used to test the sound absorption coefficients of composite structure in an acoustic range of 80–6300?Hz frequencies. Analysis was made to discuss the influence of such factors on the sound absorption properties as the position of activated carbon fiber felts, thickness, and air space. The results demonstrated that the composite structure displayed different sound absorption properties at different frequencies. Perforated panels played the dominant role in sound absorption by the occurrence of resonance at 80–3500?Hz frequencies, while porous materials contributed the most at 3500–6300?Hz frequencies. At 80–3500?Hz frequencies, the best performance could be observed in the third type of composite structure with changes in the position of activated carbon fiber; the first resonance frequency of the first type of composite structure and perforated panel structure was basically the same, and that of the remaining three types significantly shifted towards the low frequencies with the same scale. In smaller thickness range, with the increase in the thickness of activated carbon fiber felts, sound absorption coefficients of the first and second types of composite structure increased, the first resonance frequency of the first type showing no apparent shift towards the low frequencies compared with what was shown in the second type; but when the thickness arrived at 15.6?mm, sound absorption properties of the composite structure had similar traits to that performed by porous materials in an acoustic range of 80–6300?Hz frequencies. With the increase in the distance of air space, sound absorption properties were improving at 80–650?Hz frequencies but decreasing at 650–3500?Hz frequencies, the first resonance frequency moving towards the low frequencies. At 3500–6300?Hz frequencies, as the position of activated carbon fiber felts and the distance of air space varied, sound absorption coefficients were basically unchanged; while as thickness increased, sound absorption coefficients improved.     

How Does Light Intensity Affect the Elementary Fiber Length in Flax?

Abstract

There are not enough antecedents about the effect of a decrease in photosynthesis on flax stem growth and elementary fiber length. Therefore, plots sowed with cultivar Diane were shaded with nets that intercepted 70% of photosynthetically active radiation. The nets were placed at three stages of the growth period: S1: 575°Cd (height: 25 cm), S2: 854°Cd (height: 54 cm), and S3: 1304°Cd (height: 84 cm). These applications resulted in stems shadowed only in the parts, which grew during the treatment. Additionally, control plots without shadows during the entire cycle (S0) were grown. In every treatment the production of fiber was quantified, and a harvest index (HI = fiber biomass obtained/stems biomass produced) was calculated. Fiber quality was also evaluated using elementary fiber length. The harvest index was bigger in control plants than shadow plants. The length of elementary fiber of the shadow treatments S1, S2, and S3 was 4.28 cm, 3.76 cm, and 3.02 cm, respectively, whereas the adjacent portions to the shaded one in each treatment had a length fiber increase of 21%, 34%, and 37%, respectively. In the same portions, S0 had fiber lengths of 4.94, 4.45, and 3.82 cm, respectively. The trend observed in all the shaded treatments showed a decrease of elementary fiber length. The fiber length in the adjacent portions to the shaded ones was not conditioned by the shadow treatment received. These results allow relating fiber quality with stresses generated by meteorological events that take place during the growth of the stem.     

不同长度的三维四向编织复合材料T型梁模态性能研究

文章分别用实验和有限元模拟方法研究了碳纤维三维四向编织复合材料T型梁的模态性能,分析了悬臂梁自由端长度的变化对其固有频率的影响以及固有频率与阻尼性能的关系,并对比了实验和有限元模拟固有频率。结果表明:三维四向编织复合材料T型梁的固有频率随着其自由端长度的增加而降低;其固有频率和其阻尼性能没有明显的相关关系;模拟结果与实验结果相一致。     

An Investigation of the Sound Absorption Properties of Flax/Epoxy Composites Compared with Glass/Epoxy Composites

Natural fiber based composites are becoming attractive candidates for use in various applications owing to their mechanical and sound absorption properties. It has been proposed that they could potentially replace glass fiber composites owing to their minimized impact on human health and the environment. Though studies have been dedicated to understanding their mechanical properties, few focus on quantifying their sound attenuation behavior. We investigated the sound absorption properties of flax/epoxy composites and found them to be superior to those of glass/epoxy composites. A noteworthy result was that the noise reduction coefficient increased from an average value of 0.095–0.11 for unidirectional flax/epoxy composite and to 0.10 for cross-ply flax/epoxy system. Results suggest that flax/epoxy composites could be less expensive, viable and ecologically superior substitutes for glass-fiber based composites, particularly in applications where sound absorption is important.     

Effect of Freezing-Thawing on Clayey Soils Reinforced with Human Hair Fibers

ABSTRACT

The reinforcing of fine-grained soils using natural or synthetic fibers has been successfully applied today. The use of waste human hair fibers among natural fibers is seen as a sustainable solution as a reinforcing material. A series of free pressure tests were performed before and after the freezing-thawing cycle in order to examine the strength properties of the clayey soil (CS) reinforced with human hair fibers (HHF). Before freezing-thawing, clayey soil samples prepared with four different mass ratios of human hair fibers (0.5%, 1%, 1.5%, and 2% by dry weight) indicated 14–54% increases in strength, 7–49% increase were obtained after freezing-thawing. The highest strength increases before and after the freezing-thawing cycle has occurred in the mixture of CS+1.5% HHF. In addition, it was determined that the increase in pressure stress is remarkably increases with increasing human hair fiber ratio and cure time and freeze-thaw cycles. As a result, it is concluded that the CS reinforced with HHF can be utilized in cold climate zones.     

Improving the flame retardancy of PET fiber by constructing the carbon microspheres based melamine polyphosphate powder

Abstract

Carbon microspheres (CMSs) as carbon source, melamine phosphate (MP) as acid source and gas source, the integrated CMSs based MP composites (SiMP-CMSs) was in-situ prepared to improve the flame retardancy of PET fiber. A series of SiMP-CMSs/PET fiber were prepared by the melt spinning method. By investigating the thermal stability, flame retardancy, flame-retardant mode, crystallization and orientation degree of PET composite fiber, the results showed that, with the addition of 0.9?wt% SiMP-CMSs, the LOI value and vertical combustion grade of SiMP-CMSs/PET composite fiber was 27.4% and B1 level. The main flame-retardant mode of SiMP-CMSs/PET fiber was 31.33% physical barrier, 36.04% flame inhibition and 11.12% catalytic charring. The thermal decomposition temperature was delayed, and the residual amount increased from 11.34% to 16.13%. With the accelerated crystallization rate and the increased grain orientation, the aggregated structure of SiMP-CMSs/PET fiber was also optimized.     

麻纤维复合材料的结构设计与加工

通过自行设计的积木式模具,设计加工出不同立体结构的高性能麻纤维与热塑性树脂复合材料。在确定合适的成型工艺的基础上,探讨了模压成型工艺参数对产品力学性能的影响。最后对不同结构复合材料的力学性能进行了分析。     

Investigation of mechanical factor of soil reinforced with four types of fibers: An integrated experimental and extreme learning machine approach

ABSTRACT

This study investigates and compares mechanical factor (a dimensionless parameter and defined as the ratio of the compressive strength of fiber reinforced soil to that of unreinforced soil) for soils reinforced with four different fibers (three natural fibers and one synthetic fiber). An integrated methodology was utilized, including 351 laboratory experiments for obtaining data and Extreme Learning Machine (ELM) technique for developing functional relationships between mechanical factor and soil and fiber parameters. Soils reinforced with synthetic fiber (Polypropylene) and with natural fibers exhibited different characteristics when subjected to the same variation in soil parameters. This phenomenon can be attributed to the differences in surface morphology and water absorption capability of Polypropylene comparative to other natural fibers. Polypropylene–soil composite shows the maximum sensitivity to the soil moisture. It also shows the least sensitivity toward soil density and fiber content among all tested fiber–soil composites.     

稻秸秆纤维的吸湿性能

为拓展稻秸秆纤维的应用,利用扫描电镜对稻秸秆纤维的表面形态进行表征,测试了稻秸秆纤维、亚麻纤维、棉纤维在标准大气条件下的吸放湿特性,绘出了3种纤维的吸放湿回归曲线,推导出吸湿和放湿速率回归方程,对比分析了3种纤维的吸湿性能的差异。实验结果表明：稻秸秆纤维纵向具有大量沟槽,比表面积很大;稻秸秆纤维具有良好的吸湿、放湿性能,稻秸秆纤维的吸湿回潮率为9.3%,放湿回潮率为10.35%;3种纤维的吸放湿速率呈指数曲线衰减,亚麻纤维的吸放湿速率最高,稻秸秆纤维的吸放湿速率居中,棉纤维的吸放湿速率最低。     

Effects of different parameters on acoustic properties of activated carbon fiber felts

The aim of this study is to explore the effects of different parameters on acoustic properties of activated carbon fiber felts. Seven viscose-based activated carbon fiber felts with different specifications were selected to test the sound absorption coefficients in normal incidence by using transfer-function method and an impedance tube in an acoustic range of 250–6300?Hz frequencies, and to analyze the effects on acoustic properties caused by factors such as: thickness, bulk density, and fiber diameter. The result demonstrated that activated carbon fiber felts exhibited exceptional acoustic properties. As frequency increases, sound absorption coefficients of less-thick felts went upwards in the whole range of frequencies; when the thickness amounted to 9?mm, sound absorption coefficients showed a sharp increase at low frequencies and a fluctuation at high frequencies. With the increase in thickness and bulk density, sound absorption properties improved first and then impaired at the same level of frequency; with a decrease in the fiber diameter, properties enhanced at the same level of frequency. When thickness and bulk density increased and fiber diameter decreased, sound absorption coefficients of the first resonance frequency displayed an upward trend to different degrees, while the first resonance frequencies declined discrepantly.     

Effects of Humic Substances Obtained from Shives on Flax Yield Characteristics

The effects of humic substances (HS) extracted from flax shives on the fiber and seed yield of fiber flax were examined during 3 years field experiment. HS from shives consists of humic acids—5.3 gL^?1 and fulvic acids—0.7 gL^?1 were applied (6·10^–2 gL^?1 concentration, with 300 Lha^?1 of spraying liquid) in “herring-bone” stage (BBCH 13 growth stage). The HS action was evaluated in different climatic conditions and in three varieties. Application of HS on early stage of vegetation of flax plants increased fiber yield (exceeding control on 16.0–28.1%) and quality (5% of cellulose content), protein and oil content in seeds (up to 1.9–4.2% and 1.6–3.5%, respectively). Positive reply of flax plants on HS from flax shives in tested cultivars allows saying about prospects of this type of humic substances.     

基于纤维纵向显微图像的棉／亚麻单纤维识别

 针对棉/亚麻混纺纤维构成的织物,基于其单纤维纵向显微图像（纤维切段的长度约为0.5mm）,研究了纤维的自动识别方法。在纤维检测中,先对纤维图像进行去背景处理,而后运用形态学闭运算和背景区域生长相结合的方法获得纤维的目标区域,对图片中出现的玻璃划痕、干扰杂物等进行了很好的滤除。由纤维骨架垂直方向上的区域图、二值图和细化图得到它们的垂直积分投影序列,并提取这3条序列各自的变异系数CV值和平均值共计6个参数。将这6个参数作为棉/亚麻纤维的特征参数,训练最小二乘支持向量机分类器,对测试集的测试结果表明该分类器对棉/亚麻短纤维的识别率正确率平均为93.3%。     

Permeability anisotropy of flax nonwoven mats in vacuum‐assisted resin transfer molding

The resin flow characteristics of natural fiber mats must be taken into consideration in the design and optimization of liquid composite molding processes. This paper studied two common types of nonwoven mat structures produced by the parallel‐laying process and the cross‐laying process. The flax fiber orientation distribution characteristics of these mats were determined by using a fast Fourier transform (FFT) image analysis algorithm. Flax fiber mats produced by the parallel‐laying method had a prominent principal direction of fiber orientation, while mats produced by the cross‐laying method had a nearly random fiber orientation. The parallel‐laid mats showed a higher overall compressibility than the cross‐laid mats because of the tendency of nesting between layers of parallel fibers, leading to a lower porosity under the same vacuum level and thus a lower overall permeability. The cross‐laid nonwoven mats demonstrated nearly isotropic in‐plane permeability, while the parallel‐laid mats showed a much higher permeability in the principal fiber direction than in the orthogonal direction.