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Recycled needle punched jute fiber mats as a first natural fiber reinforcement system and these jute mats used as a core needle punched with recycled jute fabric cloths as skin layers as a second natural fiber reinforcement system were used for unsaturated polyester matrix composites via modifying the hand lay-up technique with resin preimpregnation into the jute fiber in vacuum. The effect of skin jute fabric on the tensile and bending properties of jute mat composites was investigated for different fiber weight contents. Moreover, the notch sensitivity of these composites was also compared by using the characteristic distance d o calculated by Finite Element Method (FEM). The results showed that the tensile and flexural properties of jute mat composites increased by increasing the fiber weight content and by adding the jute fabric as skin layers. On the other hand, by adding the skins, the characteristic distance decreased and, therefore, the notch sensitivity of the composites increased. The fracture behavior investigated by SEM showed that extensive fiber pull-out mechanism was revealed at the tension side of jute mat composites under the bending load and by adding the jute cloth, the failure mode of jute mat was changed to fiber bridge mechanism.

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Recently, the preservation of natural resources and the strict environmental regulations have forced the composite industry to find alternative fiber reinforcements and resin systems that are ecofriendly to produce compatible composites. Therefore, the need for natural fiber-reinforced composites has never been as prevalent as it currently is. Natural fibers offer renewability, biodegradability, abundance, cost savings, and low specific gravity when compared to synthetic fibers such as glass and carbon. Though the strength of natural fibers is not as great as glass or carbon, the specific properties are comparable. Currently natural fiber composites have two main issues that need to be addressed: resin compatibility and water absorption. Thus, natural fiber composites are the main subject in this special issue. The authors have focused on the following topics.In the paper entitled "Injection moulded biocomposites from oat hull and polypropylene/polylactide blend: fabrication and performance evaluation" by J. P. Reddy et al., oat hull fibre reinforced polypropylene (PP)/polylactide (PLA) based biocomposites were fabricated; their process engineering and performances were evaluated. The effect of ethylene propylene-g-maleic anhydride (EP-g-Ma) compatibilizer on mechanical properties of 30 wt% oat hull reinforced PP/PLA (90/10) blend composites was investigated. Thermal degradation parameters of the oat hull fibre were determined using thermogravimetric analysis. The effect of fibre reinforcement on crystallinity of oat hull fibre reinforced PP/PLA composites was studied by differential scanning calorimetry (DSC). Thermomechanical properties of the composites were analyzed by dynamic mechanical analyzer (DMA). The interfacial bonding between the fibre and the matrix was examined using scanning electron microscope (SEM). Significant improvement in tensile strength (40%) and flexural strength (46%) was observed with the addition of EP-g-Ma compatibilizer. DSC analysis of oat hull fibre reinforced composites showed an increase in the crystallization temperature (Tc) due to the nucleation effect of oat hull fibre. DMA results revealed that the storage modulus of PP/PLA/oat hull fibre composites was higher compared to PP/PLA blend throughout the investigated range of temperature.In the paper entitled "Studies of moisture absorption and release behaviour of akund fiber" by X. Yang et al., an effort has been made to study the moisture absorption and release behaviour of akund fiber and its mechanical performance at relative air humidity ranging from 0% to 100%. The gain and loss in moisture content in akund fiber due to water absorption and release were measured as a function of exposure time under the environment, in which temperature is 20 ∘ C and humidity is 65%. The regression equations of the absorption and release process were established. From the study, it was found that the water absorption curve of akund is similar with those of cotton and kapok, and its water absorption ability is better than those of cotton an...

Jute fiber mat reinforced unsaturated polyester matrix composites having different fiber weight contents (11, 22, 32 wt%) were fabricated by modifying the hand lay-up technique with resin pre-impregnation into the jute mats in the vacuum. Tension and three-point bending tests were carried out to evaluate the effect of fiber contents on these mechanical properties of above-mentioned composites. The results showed that as the fiber weight content increases, tensile strength and modulus increase and the improvement had occurred at 22 wt% of fiber weight content with respect to that of neat resin. As the fiber weight content increases, flexural strength and modulus increase and the improvement had occurred at 11 and 32 wt% fiber contents for the flexural modulus and strength respectively compared to those of neat resin. Fiber pull out mechanism is the failure mode revealed at the fracture surfaces under tensile loading as well as at tension side of composites under bending loading.