Harintharavimal Balakrishnan

Toughening of Polylactic Acid Nanocomposites: A Short Review

Polylactic acid (PLA) is a thermoplastic derived from renewable resources, which degrades to nontoxic compounds in landfills. With current advances in the field of nanotechnology, development of layered silicate-based PLA nanocomposites successfully created a sustainable material with enhanced physical, thermal and chemical properties, holding the future as an alternative to petroleum-based materials. However, the toughness of PLA in its pristine state and nanocomposites is often insufficient. As such, there has been tremendous effort in developing ways to improve this with incorporation of plasticizers and impact modifiers. In this review, we summarize approaches in toughening of PLA and its nanocomposites.

Mechanical, Thermal, and Morphological Properties of Polylactic Acid/Linear Low Density Polyethylene Blends

Melt blending of polylactic acid (PLA) and linear low density polyethylene (LLDPE) was performed to investigate the effects of LLDPE loadings on the morphology, mechanical and thermal properties of PLA/LLDPE blends. LLDPE was blended with PLA from 5—15 wt% and prepared by counterrotating twin-screw extruder followed by injection molding into test samples. The mechanical properties of the blends were assessed through tensile, flexural and impact testings while thermal properties were analyzed using differential scanning calorimetry (DSC) and thermogravimetric analysis. Scanning electron microscope was used to study the dispersion and particle size of LLDPE in PLA matrix. The impact strength of PLA improved by 53% with addition of 10 wt% LLDPE. However, the tensile modulus and strength, and elongation at break of PLA/LLDPE blends decreased with increasing weight ratio of LLDPE. Similarly, flexural modulus and strength also dropped with addition of LLDPE. DSC results showed that glass transition temperature (Tg) and crystallinity (X c) of PLA increased with blending of LLDPE. The LLDPE particles size was seen to increase with increasing loadings of LLDPE which explains the unexpected decrease of impact strength after 10 wt%.

Epoxidized natural rubber toughened polylactic acid/talc composites: Mechanical, thermal, and morphological properties

The aim of present study is to develop a toughened polylactic acid/talc composite. Talc and epoxidized natural rubber (ENR-50) were compounded with polylactic acid using counter-rotating twin-screw extruder followed by preparation of samples through injection molding. The effect of silane-treated talc and epoxidized natural rubber on mechanical, thermal, and morphological properties of polylactic acid was investigated. The Young′s and flexural modulus of polylactic acid improved while the impact strength values dropped with increasing talc content (20–30 wt%) indicating that talc increased the stiffness of polylactic acid with a sacrifice in toughness. Subsequently, the blending of epoxidized natural rubber (20 wt%) to polylactic acid/talc (30 wt%) revealed that the impact strength of polylactic acid/talc composites improved 448% with considerable drop in Young’s and flexural modulus. Polylactic acid/talc/epoxidized natural rubber composite contains 60% polylactic acid, 30 wt% talc, and 10 wt% ENR display optimum stiffness and impact strength. Scanning electron micrographs demonstrates that talc agglomerates at higher loadings. Thermogravimetric anlaysis indicated that thermal stability of polylactic acid/talc composite was reduced by the addition of epoxidized natural rubber due to increasing talc agglomeration.

Epoxidized natural rubber toughened polyamide 6/organically modified montmorillonite nanocomposites

The organically modified montmorillonite (OMMT)-filled polyamide 6 (PA6) nanocomposites were toughened with epoxidized natural rubber (ENR). The PA6, ENR (15–30 wt%) and OMMT (4 parts per hundered (phr)) were melt compounded using counterrotating twin-screw extruder followed by the injection molding. X-ray diffraction (XRD) results indicated that the OMMT platelets in PA6/ENR/OMMT nanocomposites were well dispersed. The Fourier transform infrared (FT-IR) spectra showed graft esterification reaction between PA6 and ENR during processing. It was found that the addition of ENR (up to 20% wt) increased the impact strength and elongation at break of the nanocomposites. Scanning electron microscopy (SEM) images revealed well-dispersed ENR particles. Differential scanning calorimetry (DSC) results showed that the presence of ENR and OMMT had negligible effect on the glass transition of PA6 with a slight decrease in crystallization temperature and crystallinity in PA6/ENR/OMMT nanocomposites.

Epoxidized natural rubber–toughened polypropylene/organically modified montmorillonite nanocomposites

The objective of this study is to toughen organically modified montmorillonite (OMMT)-filled polypropylene (PP) nanocomposites with epoxidized natural rubber (ENR). PP, ENR (10–20 wt%), OMMT (6 wt%) and maleated PP (PP-g-MA; 10 wt%) were melt blended using counterrotating twin extruder, followed by injection molding to prepare test samples. X-ray diffraction results revealed that the OMMT platelets in PP/OMMT nanocomposites were intercalated and the incorporation of ENR into the nanocomposites further increased the d-spacing of OMMT layers. The Fourier transform infrared spectra showed that the maleic anhydride group in PP-g-MA reacted in situ with the epoxy groups of ENR, which demonstrates the occurrence of grafting reaction. With slight decrease in stiffness and strength, the addition of 20 wt% ENR increased the impact strength of PP/ENR/OMMT nanocomposites by 521% compared to PP/OMMT nanocomposites. Scanning electron microscopy images revealed that the ENR particle size increased with increasing ENR contents in PP/ENR/OMMT nanocomposites. Differential scanning calorimetry results revealed that the presence of ENR and OMMT had slightly increased the crystallization temperature as well as the degree of crystallinity of PP. Thermogravimetric analysis showed that the blending of ENR decreased the thermal stability of PP/OMMT nanocomposites.

Maleated High Density Polyethylene Compatibilized High Density Polyethylene/Hydroxyapatite Composites for Biomedical Applications: Properties and Characterization

The study investigated the use of maleated high density polyethylene (mHDPE) as a compatibilizer in high density polyethylene/hydroxyapatite (HDPE/HA) composites for biomedical applications. The addition of HA increased the strength and stiffness of HDPE/HA composites while the use of mHDPE in HDPE/HA composites improved its elongation at break values. The SEM images revealed that the addition of mHDPE has induced the formation of HDPE fibrils in mHDPE/HA composites. The size of apatite layer increased with simulated body fluid (SBF) immersion time and the formation of apatite layers on the surface of composites indicates excellent biocompatibility properties.

Polylactic Acid Based Blends, Composites and Nanocomposites

Biopolymers are expected to be an alternative for conventional plastics due to the limited resources and soaring petroleum price which will restrict the use of petroleum based plastics in the near future. PLA has attracted the attention of polymer scientist recently as a potential biopolymer to substitute the conventional petroleum based plastics. The chapter aims to highlight on the recent developments in preparation and characterization of PLA blends (biodegradable and non-biodegradable blends), PLA composites (natural fiber and mineral fillers) and PLA nanocomposites (PLA/montmorillonite, PLA/carbon nanotubes and PLA/cellulose nanowhiskers).

Recent Developments in PA6/PP Nanocomposites

An overview of the recent developments in PA6/PP blend nanocomposites is presented in this paper with an emphasis on their mechanical, thermal and morphological properties. The role of organoclay as a reinforcing agent and polyethylene octene (POE) as an elastomer are discussed in detail. The organoclay increases the strength and stiffness while the POE elastomer increases the impact toughness of the nanocomposites. The effects of various parameters such as PA6/PP blend ratio, organoclay loading and the concentration of elastomer on the nanocomposites properties are also examined. The exfoliated state of organoclay platelets along with the fine particle size and uniform dispersion of POE demonstrate the nanocomposite with improved properties. These materials are attracting considerable interest in polymer research community because they exhibit substantial improvement in properties at low filler contents.

Bionanocomposites of Regenerated Cellulose Reinforced with Halloysite Nanoclay and Graphene Nanoplatelets: Characterizations and Properties

In recent years, the development of environmentally friendly materials obtained from renewable resources has attracted immense interest due to the new sustainable development policies. Cellulose is a readily available, naturally occurring biodegradable, and biocompatible linear polysaccharide. Recently, room temperature ionic liquids have been used as solvents to produce regenerated cellulose (RC) due to their attractive properties such as good chemical and thermal stability, low flammability, low melting point, and ease of recycling. Polymer/nanofiller nanocomposites are believed to have strong potential to widen polymer applications due to enhanced performance. It is also widely accepted that the incorporation of small amount of nanofiller (less than 5 wt%) into bio-based matrixes to produce nano-biocomposite materials with enhanced mechanical, permeability, and thermal properties. The tubular silica-based naturally occurring nanofiller, halloysite nanotubes (HNT), has been investigated due to its high surface area, unique geometry, and its potential to make the hydrogen bonding with polymers to disperse well in the matrix. Graphene nanoplatelets (GNP) have also attracted enormous attention among polymer engineers over the last few years due to its unique electrical, thermal, and mechanical properties. Single layer two-dimensional GNP sheet is considered as the strongest material along with the high surface area and aspect ratio. The chapter aims to highlight the effect of the addition of two different types of nanofillers such as HNT and GNP to produce RC nanocomposites on selected properties.

Preparation and Characterization of Organically Modified Montmorillonite-Filled High Density Polyethylene/Hydroxyapatite Nanocomposites for Biomedical Applications

The study investigated the introduction of organically modified montmorillonite (MMT) in high density polyethylene/hydroxyapatite (HDPE/HA) composites for biomedical applications. The addition of HA and MMT increased the strength and stiffness of HDPE/HA composites with deterioration in impact strength and elongation at break values. XRD and TEM analysis provided evidence of exfoliated MMT layers in HDPE/HA composites and the MMT layers remained exfoliated even with further addition of HA. Simulated body fluid (SBF) analysis revealed that the size of apatite layer increased with increasing immersion time and the formation of apatite layers on the surface of composites indicates excellent biocompatibility properties.