Zane Zelča

Influence of Hemp Fibers Pre-processing on Low Density Polyethylene Matrix Composites Properties

In present research with short hemp fibres reinforced LLDPE matrix composites with fibres content in a range from 30 to 50 wt% subjected to four different pre-processing technologies were produced and such their properties as tensile strength and elongation at break, tensile modulus, melt flow index, micro hardness and water absorption dynamics were investigated. Capillary viscosimetry was used for fluidity evaluation and melt flow index (MFI) evaluated for all variants. MFI of fibres of two pre-processing variants were high enough to increase hemp fibres content from 30 to 50 wt% with moderate increase of water sorption capability.

Hemp Fibers Waste and Linear Low Density Polyethylene Composite Properties

Influence of the composite preparing technology and filler type (hemp waste and hemp fibres) on the performance characteristics (melt flow index and water resistance) of the composites based on a linear low density polyethylene (LLDPE) was investigated. The best melt flow index (MFI) results were achieved when as composites preparing method extrusion and two rolls mill with lubricant additive combination were used. It is established that usage of extrusion mixing method of the hemp fibers containing LLDPE composites significantly affects materials melts fluidity evaluated by values of MFI and quality of extruded profile. The lowest fluidity was observed for composite with hemp waste prepared by two rolls mill processing method. The best water resistance was observed for composites with lubricant and for their preparing two rolls mill and extrusion processing methods combination was used.

Properties of Composites Based on Linear Low Density Polyethylene (LLDPE) and by Sol-gel Method Modified Fibres

The influence of sol-gel modified fibres content on the melt flow index (MFI) and water absorption of a linear low density polyethylene was investigated. The fibres were modified with silica xerogel prepared by the sol-gel polymerization of tetraethylorthosilicate (TEOS) under hydrolytic conditions using acid catalysis. Alkali pre-treatment was used for some variants and some composite samples were prepared by adding maleic anhydride grafted polyethylene (MA-g-PE). It was found out that melt flow index increases using sol-gel method for hemp fibres modification with fibres content in composite 40 and 50 wt%. Composite with fibres modified by sol-gel method content 40 wt% water absorption were evaluated in a range from 8.5 to 16.32%, but for composites with 50 wt% - 12.12%.

The Effect of Modification Methods on the Performance Characteristics of Composites Based on a Linear Low-Density Polyethylene and Natural Hemp Fibers

Influence of the content of hemp fibers (harvested in 2012) and their modification methods (treatment with boiling water, sodium hydroxide, and acetic anhydride) and addition of an interfacial modifier, maleated polyethylene (MAPE), on the performance characteristics (tensile strength, modulus, elongation at break, microhardness, and water resistance) of composites based on a linear low-density polyethylene (LLDPE) was investigated. The results obtained are compared with data found earlier for the same type of hemp fibers, but harvested in 2011. It is shown that optimum content of untreated hemp fibers in the LLDPE matrix is 30 wt.% and optimum length of the fibers is less than 1 mm. An increase in the content of hemp fibers (to 30 wt.%) raised the tensile strength and modulus of the composites, but reduced their elasticity and deformation ability. Simultaneously, the microhardness of the composite materials grew. Pretreating the fibers with sodium hydroxide improved the mechanical properties of the composites only slightly, but treating with acetic anhydride allowed us to elevate the content of the fibers up to 40 and 50 wt.%. The best results were achieved by addition of 50 wt.% MAPE, when the tensile modulus increased by about 47% and the tensile strength by 27% as compared with those of composites with fibers pretreated by other methods. To estimate the processing possibilities of the composites, the melt flow index (MFI) was determined. It is established that the pretreatment of the fibers significantly affects the numerical values of MFI. For example, upon treatment with acetic anhydride, a sufficiently high fluidity of the composites was retained even at a 50 wt.% content of fibers. The lowest fluidity was observed for composites with alkali-pretreated hemp fibers. The surface microhardness decreased upon their chemical pretreatment. The highest microhardness showed composites with 30 wt.% untreated fibers. The chemical pretreatment considerably raised the water resistance of the composites. Especially low water absorption was observed for composites containing MAPE and hemp fibers pretreated with acetic anhydride.