The Interface Regulation Of Bamboo Fiber Reinforced Composite Material And Its Influence On The Thermomechanical Properties

With the sustainable development of human society,some serious problems,such as resource consumpations and environmental pollutions caused by man-made composites reinforced with glass fibers and crabon fibers,have received increasing attention in recent years.Bamboo fibers have many advantages of excellent mechanical properties,low production cost,and biodegradability,which make them have a potential for replacing traditional synthetic fibers.However,natural fibers exhibit the hydrophilic character in nature.Thus,the interface compatibility becomes poor when they are frabricated with polymer matrix for ensuing composites,leading to a bearing capacity degradation.It is evident that the interface regulation has become an effective method for improving composite performance.The alkali treatment plays an action for reducing the fiber hydrophilicity by dissolving non-cellulosic materials attached on its surface,like as hemicellulose,lignin,and pectin.In this work,bamboo fibers were firstly modified by NaOH concentrations of 1,4 and 7%to investigate the influence of alkali treatment on the microstructural morphology,crystallinity,and specific surface area.The fiber physical and chemical properties were examined in turn.It was found that the cellulose crystallinity decreased as the alkali concentration increased.Also,the transformation of cellulose crystal form occurred.Furthermore,there were more pores and gaps on the fiber surface after the alkali treatment,leading to a roughness increment.However,the fiber surface were damaged when the alkali concentration increased to 7%,resulting in the fiber swelling.Secondly,the study conducted a comprehensive investigation on the influence of alkali concentration on the tensile properties,fracture morphology,crystallization behavior and thermal stability of thermosetting epoxy-based composites reinforced with bamboo fibers.The results showed that interfacial adhesion were effectively improved after the treatment.The strength reached the maximum value when alkali concentration was 4%,being increased by 45.24%compared with the untreated composites.However,the strength decreased for the case of 7%concentration.Besides,the elongation at break increased with increasing the concentration.In contrary,the composite tensile modulus decreased as the concentration increased,which was due to the fiber crystallinity degradation.The glass transition temperature(T_g)of composites increased firstly and then decreased with increasing the concentration.There was the maximum in T_g when the alkali concentration was 4%,which was increased by 7.13% compared with the untreated composites.Similarly,the composite thermal stability reached an optimum at the concentration for 4%.As one of the major factors that influence composite thermo-mechanical properties,fiber volume fractions of 0,30,50,and 70%are considered for preparing epoxy-based composites.The effects of fiber content on tensile properties,dynamic thermo-mechanical properties,glass transition temperature and thermal stability of such thermoset composites were investigated.The results indicated that the tensile strength and elongation at break of the composites increased firstly and then decreased as the fiber content increased,and they reached the maximum when V_f=50%.They increased by five times and 23.34%,respectively,in comparison with resin.In addition,the composite tensile modulus and storage modulus increased with increasing the fiber volume fraction.In this case,the peak value of loss modulus at room temperature increased,but the glass transition temperature and mechanical loss factor decreased.These results also showed that when the fibers were introduced in the matrix,the thermal decomposition temperature and thermal stability were improved.Based on the principle of single fiber extraction,the interface shear strength(IFSS)for bamboo fibers and epoxy resin were tested by fiber extraction and droplet debonding to study the effect of alkali concentrations on composite interface performance.The failure mechanism of fibers and matrix was also analyzed by combing with the interface morphology.It was shown that the fiber surface treatment could allow for a stronger mechanical interlocking effect with the matrix,which was beneficial to superior interfacial performance.Thus,the measured IFSS exhibited a similar trend,namely,it increased firstly and then decreased with the increasing concentration.Such a value reached the maximum at the concentration with 4%,increasing by 149.83%and100.61%,respectively,compared with the untreated composites.Additionally,the alkali treatment could change the interface failure mode.Specifically,fibers are debonded from the matrix,causing the interface failure when fibers are untreated.For the case of alkali treatment,the matrix is damaged before the interfacial debonding,indicating a well-bonded interface.Finally,thermoplastic composites were prepared by untreated and4%-alkali-concentration treated bamboo fibers and polylactic acid(PLA).Also,the effects of alkali treatment on the fracture morphology and thermo-mechanical properties of PLA-based composites were investigated.Importantly,the influencial mechanism of interface compatibility on some characteristic temperatures,such as the glass transition temperature,crystallization temperature,and melting temperature,and the crystallinity were also analyzed.It was discovered that the interfacial compatibility between bamboo fibers and PLA was improved by the alkali treatment,resulting in the increment in the tensile strength and elongation at break of the composite,which was increased by 49.53%and 84.61%,respectively,compared to untreated composites.Moreover,the weight loss also decreased,indicating that the composite thermal stability was enhanced.Meanwhile,the glass transition temperature and crystallization temperature were improved after the fiber surface modification,but the crystallinity decreased.The purpose of this study is to study the thermo-mechanical performance of composites reinforced with bamboo fibers,which are considered as one of typical representatives of degradable materials.The obtained results would be useful to provide essential theory basis and powerful technical support for product development and performance optimization of green composites,promoting a wider application of such new materials.