改性椰纤维增强聚乳酸复合材料力学性能

目的添加适量椰纤维(CF)改善聚乳酸(PLA)的力学性能,以适应产品的包装。方法采用熔融共混法制备不同CF含量的CF/PLA复合材料。通过力学性能测试、扫描电子显微镜观察和动态热力学性能测试,探讨添加不同含量的碱洗CF对复合材料力学性能的影响。结果与纯PLA相比,复合材料的拉伸强度降低,冲击强度增大,储能模量增大,玻璃化转变温度降低。当碱洗CF质量分数为3%时,复合材料的冲击强度比纯PLA增加了24%。结论添加CF有利于提高复合材料的力学性能,碱液浸泡更有利于改善CF和PLA基体的界面相容性。     

Tensile,flexural and torsional properties of chemically treated alfa,coir and bagasse reinforced polypropylene

Mechanical properties of alfa, coir and bagasse fibers reinforced polypropylene (PP) composites have been investigated. In order to improve the composite’s mechanical properties, fibers were alkali treated before compounding to remove natural waxes and other non cellulosic compounds. The mechanical properties of the composites obtained with these three fibers were found to be superior to those of the neat polymer. Addition of various amount of reinforcement fibers yielded noticeable increases in both tensile and flexural modulus as well as the torsion parameter. 56–75% increases in tensile modulus were observed by the use of alfa, coir and bagasse while the flexural modulus increased by 30–47% when compared to neat PP. An increase in torsion modulus is also observed when the fiber content exceeds a threshold level. A power law model was developed using an experimental data to calculate the torsion modulus of fiber-reinforced composites at various fiber loading and frequencies.     

纤维增强改性阻尼材料研究

随着高性能机械设备和高速轨道交通的飞速发展,阻尼材料已被广泛应用于解决噪声和振动问题。研究了添加不同纤维对阻尼材料性能的影响。在阻尼浆和环氧树脂两种基体中添加了有机纤维和玻璃纤维,使用DMA测试仪对复合材料动态力学性能进行表征,探讨了纤维增强机理。测试结果表明,有机纤维较玻璃纤维对复合材料的增强效果好,其中PET纤维表现出较优良的阻尼性能。     

Creep behaviour of FRP-reinforced polymer concrete

Polymer concrete is a kind of concrete where natural aggregates such as silica sand or gravel are binded together with a thermoset resin, such as epoxy. Although polymer concretes are stronger in compression than cementitious concrete, its tension behaviour is still weak. The reinforcement of polymer concrete beams in the tension zone with pultruded profiles made of epoxy resin and glass fibers are a good compromise between stiffness and strength. In this paper it is reported an investigation of the creep behaviour of polymer concrete beams reinforced with fiber-reinforced plastics (pultruded) rebars. Four-point bending creep test were performed. An analytical model was applied to verify the experimental results.     

Improvement of physico-mechanical properties of coir-polypropylene biocomposites by fiber chemical treatment

In preparing polymer–matrix composites, natural fibers are widely used as “reinforcing agents” because of their biodegradable characteristic. In present research, coir fiber reinforced polypropylene biocomposites were manufactured using hot press method. In order to increase the compatibility between the coir fiber and polypropylene matrix, raw coir fiber was chemically treated with basic chromium sulfate and sodium bicarbonate salt in acidic media. Both raw and treated coir at different fiber loading (10, 15 and 20 wt%) were utilized during composite manufacturing. During chemical treatment, hydrophilic –OH groups in the raw coir cellulose were converted to hydrophobic –OH−Cr groups. Microstructural analysis and mechanical tests were conducted. Scanning electron microscopic analysis indicates improvement in interfacial adhesion between the coir and polypropylene matrix upon treatment. Chemically treated specimens yielded the best set of mechanical properties. On the basis of fiber loading, 20% fiber reinforced composites had the optimum set of mechanical properties among all composites manufactured.     

Evaluation of mechanical properties of banana and sisal fiber reinforced epoxy composites: Influence of glass fiber hybridization

In this work, the effect of glass fiber hybridization with the randomly oriented natural fibers has been analyzed. The banana (B), sisal (S) fibers were chopped and woven E-glass (G) synthetic fibers were reinforced with epoxy matrix. Nine different kinds of laminates were prepared in the following stacking sequence of B, S, BS, G/B/G, G/S/G, G/BS/G, G/B/G/B/G, G/S/G/S/G and G/BS/G/BS/G. Mechanical properties like tensile strength, flexural strength and impact strength were evaluated and compared. Interfacial analysis was also carried out with the help of Scanning Electron Microscope (SEM) to study the micro structural behavior of the tested specimen. It was observed that the addition of two and three layer of glass fiber can improve the tensile strength by a factor of 2.34 and 4.13 respectively. The flexural properties were enhanced on banana–sisal fiber with two layers of glass fibers rather than three layers and the laminate with sisal and three glass ply offers better impact strength.     

Interfacial shear strength of a glass fiber/epoxy bonding in composites modified with carbon nanotubes

In recent years, carbon nanotubes (CNTs) grown on fibers have attracted a lot of interest as an additional reinforcing component in conventional fiber-reinforced composites to improve the properties of the fiber/matrix interface. Due to harsh growth conditions, the CNT-grafted fibers often exhibit degraded tensile properties. In the current study we explore an alternative approach to deliver CNTs to the fiber surface by dispersing CNTs in the fiber sizing formulation. This route takes advantage of the developed techniques for CNT dispersion in resins and introduces no damage to the fibers. We focus on unidirectional glass fiber/epoxy macro-composites where CNTs are introduced in three ways: (1) in the fiber sizing, (2) in the matrix and (3) in the fiber sizing and matrix simultaneously. Interfacial shear strength (IFSS) is investigated using single-fiber push-out microindentation. The results of the test reveal an increase of IFSS in all three cases. The maximum gain (over 90%) is achieved in the composite where CNTs are introduced solely in the fiber sizing.     

Solid freeform fabrication of epoxidized soybean oil/epoxy composite with bis or polyalkyleneamine curing agents

Extrusion freeform fabrication has been used to make bars of fiber-reinforced epoxidized soybean oil (ESO)/epoxy resin. Freeform fabrication methods build materials by the repetitive addition of thin layers. The mixture of epoxidized soybean oil (ESO) and epoxy resin are modified with a gelling agent to solidify the materials until curing occurs. The high strength and stiffness composites are formed through fiber reinforcement. Glass, carbon and mineral fibers are used in the formulations. It is shown that the fiber orientation follows the direction of motion of the write head that deposits the resins and has a large influence on the properties of the composite. In addition, the effects of curing agents, curing temperature, epoxy/ESO ratio, and fiber loading on mechanical properties of composites are studied and reported.     

Analysis of creep behavior in thermoplastics based on visco-elastic theory

Plastics and fiber-reinforced plastics (FRP) are used in the aerospace industry because of their mechanical properties. However, despite their excellent high-temperature mechanical properties, plastics and FRP eventually deform visco-elastically at high temperatures. Most of the research has focused on the creep behavior of FRPs, but few studies have investigated the linear visco-elastic behavior. Linear visco-elastic behavior and non-linear visco-elastic behavior occur with physical aging in these plastics. In this study, the non-linear visco-elastic behavior of plastics and FRP was investigated based on the bending creep deformation of polycarbonate (PC) and polyoxymethylene (POM). Moreover, the effects of the fiber volume fraction on the creep characteristics were investigated using glass fiber-reinforced polycarbonate (GFRPC). The creep deformation was calculated using the linear visco-elastic theory based on these effects, and comparison between experimental and estimated data showed that the creep analysis sufficiently predicted the creep behavior.     

Plant fibers and wasted fiber/epoxy green composites

In this study, the plant and waste fibers (pineapple leaf fiber, banana fiber and recycled disposable chopstick fiber) with an average length from 2.3 to 3.9 mm were chemically modified by 3-aminopropyltriethoxysilane (A1100). Subsequently, these modified fibers (20 wt.%) and epoxy resin were mixed and cured to form novel fiber-reinforced green composites. The results showed that the decomposition temperatures of the chemically modified fiber-reinforced composites were obviously higher than those of untreated fiber-reinforced composites. In addition, the tensile strengths of the reinforced epoxy composites could be increased from 80% to 117% as compared to that of the pristine epoxy. Moreover, the modified pineapple leaf fiber-reinforced composites exhibited better thermal properties than did other reinforced samples. On the other hand, modified recycled disposable chopstick fiber-reinforced composites possessed pronounced mechanical properties.     

Effect of pozzolans on the performance of fiber-reinforced mortars

Randomly oriented short fibers have been shown to increase tensile strength and retard crack propagation of cement based materials such as fiber-reinforced mortars for diverse applications, especially in aggressive environments. In the case of reinforced concrete, it is very important to produce a “high quality” cover in order to prevent corrosion of the rebars. In order to obtain a high performance material the use of a pozzolan is advisable because low permeability is achieved. The objective of this research was to determine the effect of pozzolans such as silica fume (SF), fly ash (FA), and metakaolin (MK) on the properties of fiber-reinforced mortars. Different types of natural and synthetic fibers were used. A superplasticizer was used to keep the same workability as that of the control mortar. Results of the mechanical and durability properties of the fiber-reinforced mortars are reported. The results show that a loss of resistance due to embedding fibers in mortar is compensated for by the increase in strength caused by silica fume or metakaolin additions to the mortar. The addition of 15% of SF or MK produces an improvement of up to 20% and 68%, respectively, when compared with those mortars without addition. There is a significant decrease in the coefficient of capillary absorption and chloride penetration when a highly pozzolanic material is incorporated into the matrix. In general, these materials, especially SF and MK, improve the mechanical performance and the durability of fiber-reinforced materials, especially those reinforced with steel, glass or sisal fibers. The fly ash addition had a different performance, which could be attributed to its low degree of pozzolanicity.     

Materials and mechanical properties of pretreated coir-based green composites

Chemical composition modification and surface modification of coir fibers are made in view of their use as reinforcement in coir-based green composites. Composites were prepared using coir fiber treated with varying pretreatment condition. The changes in the proportion of chemical composition and morphological properties of coir fibers with different coir pretreatment condition were discussed. It is observed that the mechanical properties of coir-based green composites; modulus of rupture and internal bond, increase as a result of chemical composition modification and surface modification. Scanning electron microscopy (SEM) investigations show that surface modifications improve the fiber/matrix adhesion.     

Nanoscale structure and local mechanical properties of fiber-reinforced composites containing MWCNT-grafted hybrid glass fibers

Carbon nanotubes (CNTs) were grown from the surface of glass fibers by chemical vapor deposition, and these hybrid fibers were individually dispersed in an epoxy matrix to investigate the local composite structure and properties near the fiber surface. High-resolution transmission electron microscopy revealed the influence of infiltration and curing of a liquid epoxy precursor on the morphology of the CNT “forest” region, or region of high CNT density near the fiber surface. Subsequent image analysis highlighted the importance of spatially dependent volume fractions of CNTs in the matrix as a function of distance from the fiber surface, and nanoindentation was used to probe local mechanical properties in the CNT forest region, showing strong correlations between local stiffness and volume fraction. This work represents the first in situ measurements of local mechanical properties of the nano-structured matrix region in hybrid fiber-reinforced composites, providing a means of quantifying the reinforcement provided by the grafted nanofillers.     

Toughening of carbon fiber-reinforced epoxy polymer composites utilizing fiber surface treatment and sizing

Toughening of fiber-reinforced epoxy composites while maintaining other mechanical properties represents a significant challenge. This paper presents an approach of enhancing the toughness of a DGEBA/mPDA-based carbon fiber-reinforced epoxy composite, without significantly reducing the static-mechanical properties such as flexural properties and glass transition temperature. The impact of combining an UV-ozone fiber surface treatment with an aromatic and aliphatic epoxy fiber sizing on composite toughness is investigated. Carbon fiber-epoxy adhesion was increased as measured by the single fiber interfacial shear test. The Mode I composite fracture toughness was enhanced by 23% for the UV-ozone fiber surface treatment alone. With the addition of an aromatic and aliphatic fiber sizing, the composite fracture toughness was further increased to 50% and 84% respectively over the as-received, unsized fiber. The increased fiber/matrix adhesion also improved the transverse flexural strength.     

Dynamisch-mechanische Analyse naturfaserverstärkter Kunststoffe

Dynamic-mechanical analysis of natural fiber reinforced plastics Recently natural fibers are increasingly used as reinforcement in plastics. These materials are distinguished by their high tensile strength and stiffness as well as their low density at the same time. For technical applications the material behaviour in addiction of temperature is very interesting. Useing the example of flax fiber reinforced polypropylen it is shown, that the dynamic-mechanical analysis can be a meaningful test to describe the behaviour of natural fiber composites by different temperatures.     

Determination of tensile strength of glass fiber straps

Glass fibers straps have been used for strengthening of masonry and concrete structures in the last decade. Recently, their use has become greater. This paper describes the research of measuring tensile strength of dry glass fiber straps as well as straps that were made of glass fibers and epoxy coating. The effect of strap widths, the effect of loading speeds and the effect of epoxy coating placed on fiber straps, on tensile strength of straps have been analyzed. Differences of tension strengths of fiber straps with and without epoxy coating are shown.     

天然纤维/环氧树脂-混凝土的力学性能及老化规律天然纤维/环氧树脂-混凝土的力学性能及老化规律

环氧树脂-混凝土是由混合树脂、固化剂和砂石骨料等原料固化成型的一种复合材料,因其优异的性能已成为土木与建筑应用中富有潜力的新型工程材料。本文将高性能的天然纤维（剑麻和苎麻）引入环氧树脂-混凝土中,以进一步增强其力学性能。实验结果表明,极少含量的天然纤维便能够提升环氧树脂-混凝土的抗弯拉强度,体积分数为0.36vol%的剑麻纤维和苎麻纤维可以将混凝土的抗弯拉强度分别提高10.5%和8.4%。天然纤维对环氧树脂-混凝土抗弯拉强度的增强效应可以用基于混合率的并联模型描述,模型预测结果与实测结果相比,相对误差低于5.1%。利用紫外光耐气候试验箱模拟华南地区自然环境的日照辐射和湿热条件,研究了天然纤维/环氧树脂-混凝土抗弯拉性能随老化时间的衰减。当等效老化时间为6年时,天然纤维/环氧树脂-混凝土的抗弯拉强度分别下降了14.3%（剑麻纤维）和15.9%（苎麻纤维）。实验观察到的衰减规律可采用复合材料湿热老化的剩余强度模型描述。      

Studies on fly ash/coir/sugarcane reinforced epoxy polymer matrix composite

In the past years studies were conducted on natural fibre reinforced polymer composites to observe their mechanical properties in order to decide their industrial applications. These composites have already been used in many applications from aerospace to sporting equipment. These green composites can be used as a replacement for synthetic composites. This is because the natural fibres are eco-friendly, biodegradable, renewable, etc. In this work, an attempt is made to reinforce fly ash, coir fibre and sugarcane fibre with epoxy polymer matrix. Central composite design under response surface methodology (RSM), one of the approaches of design of experiments (DOE) is used to determine optimum sample preparation conditions of fly ash, coir fibre and sugarcane fibre. Both tensile and flexural (three-point bending) tests are conducted on these fabricated composites to determine their materialistic characteristics. Analysis of variance (ANOVA) is carried out using Minitab software to find the influence of fly ash, coir fibre, sugarcane fibre on composites. Regression equations obtained from analysis of variance is used to calculate values. Experimental and calculated values are compared and their error % are calculated and tabulated. Response surface optimization study is carried to find the optimized parameters of composites. It is observed that, increase in wt.% of coir fibre and decrease in wt.% of fly ash and sugarcane fibre, increases yield stress and these parameters have mixed impact on ultimate tensile stress. The addition of fly ash, coir fibre and sugarcane fibre in low percentages increases Young's modulus. Increase in wt.% of fly ash and coir fibre and decrease in wt.% of sugarcane, increases flexural modulus and flexural stress.     

Reinforcing hydroxyapatite/thermosetting epoxy composite with 3-D carbon fiber fabric through RTM processing

Bioactive ceramic/polymer composites have been developed in the orthopaedic field in recent years. In this work, three-dimensional (3-D) carbon fiber fabric is used to reinforce hydroxyapatite (HA)/thermosetting epoxy composite and epoxy resin through resin transfer molding (RTM) processing. It is found that the 3-D carbon fiber fabric can be impregnated with epoxy and HA-containing epoxy resin, and HA is distributed gradually along the depth direction in fiber-reinforced HA/epoxy composite, although HA is dispersed evenly in epoxy resin by surface modification of silane coupling agent. The impact toughness and flexural strength of fiber-reinforced epoxy and fiber-reinforced HA/epoxy composites are much higher than those of epoxy and HA/epoxy composite. The impact toughness of both fiber-reinforced composites decreases while the flexural strength and the flexural modulus increase with fiber volume ratio. The impact toughness of the fiber-reinforced HA/epoxy composite is higher, while the flexural strength and modulus are lower than those of the fiber-reinforced epoxy composite at the same fiber volume ratio. The flexural strength of the both composites is higher than, and their flexural modulus is close to, those of the human cortical bone. The in vitro cytotoxicity test with L929 fibroblasts shows that the addition of HA diminished the toxicity of epoxy resin.     

Processing and characterization of solid and microcellular PHBV/coir fiber composites

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/coir fiber composites were prepared via both conventional and microcellular injection-molding processes. The surface of the hydrophilic coir fiber was modified by alkali- and silane-treatment to improve its adhesion with PHBV. The morphology, thermal, and mechanical properties were investigated. The addition of coir fiber (treated and untreated) reduced cell size and increased cell density. Further decrease in cell size and increase in cell density was observed for treated fibers compared with PHBV/untreated-fiber composites. Mechanical properties such as specific toughness and strain-at-break improved for both solid and microcellular specimens with the addition of coir fibers (both treated and untreated); however, the specific modulus remained essentially the same statistically while the specific strength decreased slightly. The silane-treated coir fiber composites showed the greatest improvement in specific toughness and strain-at-break among the treated-fiber composites. In addition, adding coir fibers (treated and untreated) also increased the degree of crystallinity of the PHBV composites. PHBV with treated coir fibers showed a higher degree of crystallinity compared with untreated coir fibers.