Author(s):
1. Silvester Bolka, VŠTP, Slovenia
2. Janez Slapnik, VŠTP, Slovenia
3. Rajko Bobovnik, VŠTP, Slovenia
4. Maja Mešl, VŠTP, Slovenia

Abstract:
Biocomposites of hemp fiber reinforced bio-based high density polyethylene (green PE-HD) were prepared using a maleic anhydride grafted styrene–ethylene/butylene–styrene (SEBS-g-MA) as a compatibilizer. Several compositions of biocomposites were prepared on a tween screw extruder using the full factorial design (design of experiments, DoE) varying two factors with two levels. The addition of hemp was 2 wt. % and 10 wt. %, the addition of SEBS-g-MA was 0 wt. % and 2 wt. %. In addition to four compositions, the central point experiment was carried out as a control as well as the neat green PE-HD as a reference. Test specimens were prepared by injection molding according to standards ISO 527 (form 1BA), ISO 178, and ISO 179. The mechanical and thermal properties were investigated by tensile and bending tests, DMA, and ultra-fast differential dynamic calorimetry (Flash DSC). Tensile E modulus was higher with the addition of the hemp (at 2 wt. % hemp for 6 % without SEBS-g-MA and for 13 % for 2 % SEBS-g-MA; at 10 wt. % hemp for 25 % without SEBS-g-MA and for 30 % for 2 % SEBS-g-MA) and also tensile strength was in all versions higher (at 2 wt. % hemp for 8 % without SEBS-g-MA and for 11 % for 2 % SEBS-g-MA; at 10 wt. % hemp for 9 % without SEBS-g-MA and for 25 % for 2 % SEBS-g-MA). High E modulus and tensile strength in comparison to neat green PE-HD indicate very good compatibility of the constituents of biocomposites. The results of DMA and bending tests support the results of tensile test. E moduli of the samples without SEBS-g-MA are slightly higher than those of the samples with SEBS-g-MA. The thermal stability of biocomposites is for all samples drastically higher as compared to neat green PE-HD. As shown by DMA, E modulus at 100 °C increases from 80 % to 178 %. The melting point (Tm) and crystallization temperature (Tc) of biocomposites were determined by Flash DSC. Tm at the cooling rate of 10 °C/min is shifted from 120 °C (neat green PE-HD) to 121 °C and up to 130 °C, whereas Tc is shifted from 111 °C (neat green PE-HD) to 116 - 117 °C. At the cooling rate of 1,000 °C/min Tc is shifted from 78 °C (neat green PE-HD) to 91 - 95 °C. The novel biocomposites are suitable for applications requiring higher stiffness and thermal stability as compared to neat green PE-HD, such as technical parts.

Key words:
high density polyethylene (PE-HD), hemp fiber, maleic anhydride grafted styrene–ethylene/butylene–styrene (SEBS-g-MA), characterization

Thematic field:
SYMPOSIUM B - Biomaterials and nanomedicine

Date of abstract submission:
04.07.2016.

Conference:
Contemporary Materials 2016 - Savremeni Materijali