Sunil K. Varshney

Polylactides—Chemistry, Properties and Green Packaging Technology: A Review

Polylactide (PLA), a biodegradable aliphatic polyester, has been studied extensively for its wide applications in various fields from food packaging to interior materials for automobiles. One of PLAs advantages is that the raw material, lactic acid can be derived from renewable resources, which makes PLA very attractive for the packaging and considered as green packaging. Although, the cost of PLA is relatively higher compared to petroleum based packaging materials and it is predicted that the price will go down after commercial success of the process. This paper presents a review on polylactide with focus on its chemistry, synthesis, properties, and applications. Plasticization effect on PLA, sorption isotherm and mechanical properties of PLA based packaging materials have been discussed. PLA/layered organo nanocomposites exhibit significant improvement in mechanical, thermal, optical, and physicochemical properties over pure PLA. This review includes brief overview of PLA based nanocomposite, their mechanical properties, potential as packaging materials for industrial usage and their environmental implications.

Thermal and rheological properties of L-polylactide/polyethylene glycol/silicate nanocomposites films.

The melt rheology and thermal properties of polylactide (PLA)-based nanocomposite films that were prepared by solvent casting method with L-PLA, polyethylene glycol (PEG), and montmorillonite clay were studied. The neat PLA showed predominantly solid-like behavior (G > G″) and the complex viscosity (η*) decreased systematically as the temperature increased from 184 to 196 °C. The elastic modulus (G) of PLA/clay blend showed a significant improvement in the magnitude in the melt, while clay concentration was at 6% wt or higher. At similar condition, PEG dramatically reduced dynamic modulii and complex viscosity of PLA/PEG blend as function of concentration. A nanocomposite blend of PLA/PEG/clay (74/20/6) when compared to the neat polymer and PLA/PEG blend exhibited intermediate values of elastic modulus (G) and complex viscosity (η*) with excellent flexibility. Thermal analysis of different clay loading blends indicated that the melting temperature (T(m)) and glass transition temperature (T(g)) remained unaffected irrespective of clay concentration due to immobilization of polymer chain in the clay nanocomposite. PEG incorporation reduced the T(g) and the T(m) of the blends (PLA/PEG and PLA/PEG/clay) significantly, however, crystallinity increased in the similar condition. The transmission electron microscopy (TEM) image of nanocomposite films indicated good compatibility between PLA and PEG, whereas clay was not thoroughly distributed in the PLA matrix and remained as clusters. The percent crystallinity obtained by X-ray was significantly higher than that of differential scanning calorimeter (DSC) data for PLA.

Rheological and thermal properties of stereocomplexed polylactide films

Poly(l-lactide) (PLLA) and Poly(d-lactide) (PDLA) blended films (PLLA/PDLA) were prepared (5/95; 25/75; 50/50, and 75/25) by solvent casting method. Blend of PLLA and PDLA of medium molecular mass led to the formation of stereocomplex which was evidenced by differential scanning calorimetry, rheological measurement and Fourier transform infrared spectroscopy. The stereocomplex had a higher melting temperature (Tm) (more than 50xa0°C) and crystallized at higher temperature (Tc) (more than 25xa0°C) from the melt compared to neat PLLA and PDLA. The Tm and Tc gradually decreased with increasing the number of thermal scans. The enthalpy of fusion (∆Hm) for stereocomplex crystallites in 50/50 blend films was the highest than that of homo-crystallites. Rheological measurement at a temperature of 180–195xa0°C revealed that the neat PLA was predominantly liquid-like behavior (G″xa0>xa0G′) which transformed to extreme solid-like behavior by incorporation of PDLA into PLLA. Among blends, 50/50 PDLA/PLLA showed the maximum mechanical strength (G′) followed by 25/75, 75/25, and 5/95 blends. The significant increase in mechanical strength is believed to be attributed by stereocomplex formation by blends. Thermal and rheological data supported higher mechanical strength and an increase in melting and crystallization temperature adequately.

Synthesis and thermal properties of poly(vinylcyclohexane)-b-poly(4-vinylpyridine) diblock copolymers prepared via RAFT polymerization

Abstract A series of novel poly(vinylcyclohexane)-b-poly(4-vinylpyridine) (PVCH-b-P4VP) diblock copolymers have been synthesized through a combination of anionic and RAFT polymerization techniques. Using this approach, end functionalized ω-hydroxy-polystyrene was used to yield ω-hydroxy-PVCH by hydrogenation followed by end-functionalization via an esterification reaction with 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid to yield PVCH-RAFT agent. The crossover propagation from PVCH-RAFT to 4VP displays living character and allowed generating diblock copolymers with well-defined molecular compositions. The characterization of the resulted polymers was performed using 1H nuclear magnetic resonance (NMR) and Fourier-transform infra-red (FT-IR) spectroscopies, size-exclusion chromatography with light-scattering detector (SEC-LS), and the thermal properties were studied using differential scanning calorimetry (DSC).

Synthesis and thermal properties of triblock copolymers of methyl methacrylate using combination of anionic and controlled radical polymerization: Poly(methyl methacrylate) center block bearing different microstructures

Abstract ABA and/or ABC type triblock copolymers were synthesized by living anionic and controlled radical polymerization in which poly(methyl methacrylate) was used as central block. The structural composition of these block copolymers were determined by 1H NMR. The block length/molecular weight and microstructure of these polymers were measured by SEC. The microstructure of resultant central alkyl methacrylate block can be tailored from highly syndiotactic to highly isotactic structure by varying the solvent and/or initiator. The thermal and rheological properties of center poly(methyl methacrylate) block and poly(styreneb- methyl methacrylate-b- styrene) tri block copolymers were studied in detail.

Synthesis of poly(styrene-block-ethylene oxide) copolymers by anionic polymerization and acid cleavage into its constituent homopolymers for the formation of ordered nanoporous thin films

Abstract Well-defined cleavable poly(styrene-block-ethylene oxide) polymers were prepared by living anioinc polymerization, using cumyl potassium as the initiator. These polymers contained an acid cleavable moiety, such as diphenyl methyl or anthracenyl methyl ether linkage, between polystyrene and poly ethylene oxide block. Atomic force microscopy (AFM) studies on the thin films illustrate the formation of nanoporous architecture due to acid cleavage of the polyethylene oxide fraction.