Thermal, Mechanical and Antibacterial Properties of Ldpe/Starch Bio-Based Polymer Blends for Food Packing Applications

Abstract

Abstract:In this study, low density polyethylene (LDPE) was melt-blended with starch using twin screw extruder to form biodegradable polymer blends. The LDPE/starch blend films used in food packing were obtained by hot pressing of the granules produced by extrusion process. The starch content was varied from 0 to 40 wt% of LDPE. To provide fine starch dispersion, glycerol and zinc stearate were used as plasticizer and compatibilizer, respectively. The effect of starch content on the properties of LDPE film was investigated. A good dispersion was achieved for low starch contents (10 and 20 wt%), but agglomeration of the starch particles occurred in the presence of high amounts of starch (>20 wt%). The addition of starch to LDPE reduced the tensile strength, elongation at break, crystallinity, and water resistance of LDPE. This decline in the LDPE properties was dramatic when the starch content was increased to 30 wt% in the blend. In addition, silver nanoparticles as antibacterial agent were incorporated to the biodegradable LDPE blends where LDPE/starch weight ratio of 60/40. The effects of these nanoparticles on morphological, mechanical, thermal and water resistance properties of the LDPE/starch biodegradable blends were investigated. It was observed that the incorporation of nanoparticles to the LDPE/starch blend was completely changed the morphology of the film, and accordingly, the mechanical, thermal, and water resistance properties were varied depending on the silver nanoparticle content in LDPE/starch blend film. Moreover, antibacterial activities of the nanocomposite films against gram-negative bacteria (E. coli) and grampositive bacteria (S. aureus) were determined by measuring the inhibition zone around each film. However, the nanocomposite films did not show any antibacterial activities in the presence of silver nanoparticles as an antibacterial agent.

Mechanical properties and crystallinity of linear low density polyethylene based biocomposite film

“…The reason for brittleness of starch has been explained elsewhere. Similar results were reported by Yamak (2016) and Sanyang et al (2015). Thermal aging of the starch/LLDPE film at 70 ± 2°C for 168 ± 2 h changes the TS and EB trends as described in the previous paragraph.…”

Investigation of physical and rheological properties of LDPE/HDPE/thermoplastic starch biodegradable blend films

“…Starch acts as a rigid dispersed phase and reduces chain flexibility of PEs and inhibits close packing of the PEs chains during the cooling process which in turn decreases the X c value. Therefore, as TS content increases, the crystallinity of the samples decreases 18,33,34 . Another reason for the decrease in the X c value with the increase of starch is the decrease of the PE in the blend 22 …”

“…The smooth and uniform continuous surface in the images can be due to the relatively good surface adhesion between the matrix and the starch which can be attributed to the presence of HDPE and glycerol. The HDPE forms well‐organized spherulites with a high degree of crystallinity and rigid amorphous layers between the lamellae, when HDPE is blended with LDPE creates rigid amorphous layers between the lamellae in the matrix, 30 and since starch particles are predominantly in the amorphous phase surrounded by the crystalline region, 18,33 it is expected that by adding HDPE, TS (plasticized starch) will be well embedded into the matrix. The role of glycerol as a plasticizer reduces the interfacial energy between the starch and matrix phases and makes them more compatible in these weight ratios 6 .…”

“…Therefore, as TS content increases, the crystallinity of the samples decreases. 18,33,34 Another reason for the decrease in the X c value with the increase of starch is the decrease of the PE in the blend. 22…”

“…This morphology is usually for incompatible mixtures which results in poor mechanical properties. 33,35,36…”