Effects of montmorillonite (MMT) on morphological, tensile, physical barrier properties and biodegradability of polylactic acid/starch/MMT nanocomposites

Abstract

Biodegradable polymer nanocomposites have received great attention due to their synergistic properties of good mechanical and barrier properties; yet, they are biodegradable. In this research, prior to compression into thin sheets, polylactic acid (PLA), tapioca starch, glycerol and maleic anhydride (MA) were compounded with different loadings of montmorillonite (MMT) through a twin screw extruder. MMT was added to improve the mechanical and barrier properties of PLA/starch blend. The effects of MMT loadings on tensile property, morphology and biodegradability were studied. X-Ray diffraction analysis showed that samples with MMT loadings below 6 phr exhibited exfoliated structure, while samples that contained MMT above 6 phr (5.66 wt%) exhibited intercalated structure. The exfoliated-type structure was observed using transmission electron microscopy. These effects were manifested in the tensile results, which showed an increase in modulus, tensile strength and elongation at break. However, for the modulus, the MMT content was limited to 4 phr (3.85 wt%). Beyond that, the modulus decreased. It was thought that above 4 phr, the MMT particles agglomerated, thus reducing the modulus of the samples. This argument was supported by field emission scanning electron microscopic images, which showed big lump when MMT loadings were at 6 and 8 phr (7.41 wt%). Meanwhile, the addition of MMT has improved the water barrier property and hastened the rate of biodegradation. The nanosized MMT particles disturb the continuity of PLA/starch chain, which formed pathways for microorganisms to enter and attack the chain, thus increasing the biodegradation rate. The particle is also able to block a tortuous pathway for water to enter the starch chain, thus reducing the water uptake and improving the physical barrier of nanocomposite.

Poly(lactic acid)—Mass production, processing, industrial applications, and end of life

“…The reinforcement phase can be fibers and/or micro and nano particles. The main goal of adding a reinforcement phase to PLA is to tailor its properties, such as elongation at break [81,[132][133][134][135][136][137][138][139][140][141], heat resistance [138,142,143], dimensional stability [137,[144][145][146][147], barrier [132,137,140,148,149], and cost [150], to overcome some of PLA's shortcoming properties compared with fossil commodity polymers, as well as brittleness and low thermal stability [2]. Since the main engineering properties of a composite result from the discontinuous phase, PLA has been reinforced with natural and synthetic fibers, micro and nano fillers [73,151].…”

“…Lately, the addition of nanoparticles has gained attention since adding nanoscale clay particles results in significant improvement of material performance. Some of the specific nanocomposite properties that are enhanced through the exfoliation of these nanoparticles include mechanical [152][153][154][155][156][157][158][159][160], barrier [132,137,140,148,149,160,161], and thermal properties [156,157,160]. The mechanical property of polymers with a nanoclay loading of 3-6% can achieve equivalent mechanical properties (i.e., tensile strength, impact strength, flexural modulus) to a polymer with up to 30 wt% fillers at the microscale (i.e., glass and mineral fibers, etc.)…”

Toughening of Poly(lactic acid) and Thermoplastic Cassava Starch Reactive Blends Using Graphene Nanoplatelets

“…The blending of PLA with other polymers and the incorporation of nanofillers into the PLA matrix have been pursued to overcome some of the polymer’s shortcomings [ 5 , 6 , 7 , 8 , 9 ]. PLA has been blended with polyethylene glycol, ethylene vinyl alcohol, poly(butylene adipate- co -terephthalate), and other polymeric systems to improve crystallinity, biodegradability, and thermal and mechanical properties [ 10 , 11 , 12 ].…”

Crystallization and thermal properties of polylactide/palygorskite composites

“…Hence the leaching or plasticization by the de‐bonded surfactants which can interact with the PLA matrix could be a reason for this observation. Jalavandi et al also observed a reduction in T g from 59 to 54°C for PLA containing 4 wt % MMT in presence of 28% starch and 12 wt % glycerol due to plasticizing effect.…”