Biodegradable Polyesters Reinforced Using Starch Granules And Functionalized Using Pomegranate Rind

Background:Food packaging is one of the largest growing sectors within the domain of plastic packaging market.The use of suitable packaging material helps in keeping the product freshness and quality over an extended duration of time.However,the polymers that are currently used as plastic packaging materials are non-degradable and represents a major global environmental problem.On the other hand,degradable polymers lack commercial success due to their high cost and inferior mechanical properties than that of non-degradable polymers.In this regard,the development of low-cost environment-friendly plastic packaging material,with optimized mechanical properties,will be highly beneficial for commercial applications.Objectives and methodology:Blending or compositing is an important approach to address the performance issues of biodegradable polymers.Furthermore,reinforcement of biodegradable polymers with naturally occurring polymers,like starch granules,holds great potential in reducing the cost of biodegradable polymers.The objective of this work was to develop low-cost,environment friendly,food-grade plastic packaging material.Two kinds of biodegradable composites were developed and characterized:(1)Poly(lactic acid)(PLA)/starch composites;and(2)Polycaprolactone(PCL)/starch/pomegranate rind(PR)hybrids.Extrusion technique was utilized to develop all the samples to ensure that the materials developed in this work are also viable for production on commercial scale.Target-1:To study how the starches from different botanical sources effect the performance of PLA/starch composites through investigating the microstructure(i.e.,amylose to amylopectin ratio)and morphology(i.e.,particle shape and particle size)of starch granules.The most popular ten different starches were used as model materials to investigate the relationship between starch microstructure and the performance of PLA/starch composites.Two-stage compounding extruder was utilized to develop PLA/starch composites.Furthermore,small concentration of biomax(i.e.,5%w/w on the basis of PLA)was also incorporated in all the samples in order to enhance the toughness characteristics of the composites.It was found that:(i)composites filled with either well-sized(small-sized and non-agglomerated)starch granules or those containing high amylose content(G-50 and G-80)improves the reinforcing ability of PLA,with least reduction in deformation;(ii)aggregation tendency of small-sized starch granules can be controlled using surface modification approach that not only reduces the phase-separation between starch and PLA but also improves the dispersion;and(iii)no discernible relationship exists between the starches,from different botanical sources,and the thermal performance of PLA/starch composites.Innovation and future recommendations:Several articles and patents have been published in this area.However,the starches used to develop such composites belong to different botanical sources that exhibit different microstructure and morphology.This results in confused relationship and no comparison of data for applications.In our study,we utilized starches from ten different botanical sources having different microstructure and morphology to avoid this confusion.Concentration of surface modifying agent(i.e.,stearic acid)needs to be optimized,keeping in view the differences in botanical origin of starches,as a recommendation for future work.Target-2:To study and develop the PCL/starch/PR hybrids for antimicrobial packaging applications.PR was used as an active compound and was incorporated directly(for the first time)in polycaprolactone(PCL)matrix,without the extraction of any active compound from the fruit rind.PCL/PR films demonstrated reasonably good antimicrobial activity only at higher concentration of PR particles.Addition of starch not only lowered the cost but also improved the rigidity of PCL matrix.Adding to this,starch enhanced the antimicrobial activity of PR and provided a releasing channel for the delivery of antimicrobial compounds by attenuating the interactions between PCL and PR.The results of FTIR analysis and tensile fracture interface study agreed with polyphenols release study whereby the concentration of polyphenols released from samples containing both starch granules and PR particles was found to be higher than those samples containing only PR particles as filler.Innovation and future recommendations:Two of the key-issues in designing active packaging materials filled with naturally occurring active compounds are the low decomposition temperature and high cost of such active compounds.In our study,we incorporated pomegranate rind directly in PCL matrix,for the first time,without extracting polyphenols to avoid high cost incurred by the deep treatment of fruit rind.Furthermore,PCL matrix was used as base material as it can be processed at temperature(melting point of PCL is~65~oC)that is much lower than the decomposition temperature of naturally occurring active compounds(<120~oC).Combination of 2 or more sources of phenolic rich waste materials can be utilized in future to enhance the effectiveness of such active packaging materials against the variety of micro-organisms.Final Remarks:The results provide an economical approach to functionalize biodegradable polyesters for commercial applications.The findings of the first project provide practical guidelines to develop PLA/starch composites and can also be utilized in designing other materials filled with starch granules.The findings of the second project are beneficial in designing active packaging materials filled with naturally occurring active compounds and might increase the use of phenolic rich waste materials in film production.Since,all the materials used in this work are food grade and biodegradable,it is expected that the materials developed in this work can be employed as food grade biodegradable packaging material.