| As a kind of natural polymer materials, palm fiber is attracting more and more people and applied into hydraulic, environmental, paper-making, elastic and composite engineering, due to its huge production, excellent anti-corrosion, pretty good moisture regain and elasticity. Deep research of properties is very essential to make the most use of fiber materials and enhance fabrics values. Structural and mechanical characteristics are thought to be the most fundamental but most important aspects for the application of fiber materials.In the paper, palm fiber and single fiber were observed using optical microscope, SEM and TEM with the aim of revealing the surface, cross-sectional, longitudinal features. Additionally, an accessible degumming process was introduced on the basis of common degumming methods of natural fibers. Palm fiber was subjected to monotonic tensile load at four different gauge lengths (10,20,30, and40mm) under the speed of0.5mm/min according to ASTM D3379-75. To learn tensile property of palm fiber deeply, two and three traditional Weibull distribution models together with modified Weibull were introduced to study the tensile property of palm fiber, and comparison was taken out between palm and sisal fiber. The results show that:(1) Palm fiber has larger size in diameter than other common natural fibers with majority ranging between300μm to450μm. A plenty of Si particles are listed along fibers on the surface. Palm fiber is about round with a great range of hollow and parallel single fibers linked with each other tightly, and that makes a palm fiber as an unidirectional composite. TEM shows the three main parts of fiber cell:lumen, primary wall and secondary wall. KClO3combined with HNO3can separate palm single fibers efficiently, and the fiber cells have convolutions along their length with tapered ends but are broader and ribbon like at the center. There are tiny stripes on the surface of fiber cell, which are thought to be of great importance to fast fiber cells with each other. The diameter and length scatter with uneven values.(2) The typical stress-strain curve shows a yield and contains three main parts. The tensile properties have a characteristic of scatter:both fiber strength and breaking strain decrease, whereas Young’s modulus increases with the increase of gauge length. During loading, the orientation change of fibrils inside let fiber behave distinctively in tensile process. SEM shows the unsmooth fracture surface and the four main states:the delamination between fiber cells, fracture of fiber cells, delamination inside fiber cells and tearing of fiber cells. Because of thicker cell wall, lower cellulosic content and lower crystallinity, palm fiber shows to be more sensitive to gauge length.(3) The parameters can be estimated through MLE. The fitting degree test can be implemented through Anderson-Darling (AD) method which perfectly corresponds to. Palm fibers exhibit a linear distribution in tensile strength, and the datum is mostly located between the two confidence interval curves of traditional Weibull models. Weibull modulus m decreases with the increase in gauge length, which means that strength variation increases as the gauge length increases. Weibull plots tell the similar linear strength distribution of jute and palm fibers; also the good degree of linearity of linear regression data and experimental data confirms the applicability of Weibull models. The smaller scatter and lower strength of palm fiber can be explained as the lower cellulosic content and lower crystalinity effect. Modified Weibull introduces a diameter parameter into analysis, and the parameter can be calculated from the linear relationship between gauge length and diameter. The modified Weibull plots also show that the Weibull modulus increases with the decrease of gauge length. Compared to sisal and jute fibers, palm fiber is more sensitive to gauge length due to the differences of structure features and pretreatment processes. |
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