Development of packaging film from Napier cellulose nanowhisker reinforced polylactic acid (PLA) bio-nanocomposites

The application of biodegradable biopolymer as packaging material have been great attention but is limited because of poor desired properties. The incorporation of cellulose nanowhisker (NWC) into the polylactic acid (PLA) matrix was developed to overcome the limitation of PLA matrix properties. The NWCs used were synthesized from Pennisetum purpureum fibres or Napier fibres then subjected to several mechanical and chemical treatments to remove the non-cellulosic materials. The fibres were divided into three groups according to acid hydrolysis reaction time; 30 min, 45 min and 60 min, denoted as NWC1, NWC2 and NWC3, respectively. TEM analysis revealed that the smallest diameter and length were obtained from NWC3—all three samples presented in a needle-like shape observed under TEM and AFM. However, uneven length and irregular shape of NWCs were obtained from FESEM analysis. The broad size distribution of NWCs samples was obtained from PSA analysis were compared to TEM, FESEM and AFM. All three samples exhibited a good crystallinity index (CI) from 72.0 to 74.6 %, of which the highest CI % corresponded to the NWC3 (60 min). Based on TGA analysis, the thermal stability was acquired between 310.72 °C to 336.28 °C. Therefore, there is a high potential of cellulose nanowhisker from Napier fibres to be utilised in the bio-nanocomposites application, especially NWC3. The reinforcement of PLA matrix by NWC3 was developed to investigate the efficiency for packaging application. PLA/NWC bio-nanocomposite film was prepared using solvent casting method with varying concentrations of NWC (0, 0.5, 1.0, 1.5, 2.0 and 3.0 wt%). FESEM showed the excellent dispersion of NWC in the PLA matrix occurred with NWC concentrations of 0.5 – 1.5 wt%. This was related to the great interfacial interaction between PLA and NWC. All the bio-nanocomposite film samples exhibited prominent thermal stability at approximately 343 – 359 °C. The highest water absorption was 1.94 %, correlated with a large amount of NWCs. The transparency is as lowest as 16.16 % at λ800 for the PLA/3.0% NWC bio-nanocomposite film. But 1.0 wt% of NWC of the bio-nanocomposite film exhibited the lowest transmittance of UVA and UVB at only 7.44 % and 3.65 %, respectively, making it suitable for packaging materials that can protect the product from defected though the transparency was at only 20.28 % at λ800. The PLA/1.0 % NWC film exhibited the highest crystallinity of 50.09 % and high tensile strength and tensile modulus of 21.22 MPa and 11.35 MPa, respectively. In conclusion, for this initial study, 1.0 wt% of NWC in PLA/NWC bio-nanocomposite film is the most capable film sample to give the favourable characteristics that meet the packaging potential in many properties improvements.