Reactive processing-microstructure-mechanical performance correlations in biodegradable poly(lactic acid)/expanded graphite nanocomposites.

Reactive extrusion is a promising method to prepare biodegradable nanocomposites with enhanced modulus, strength and toughness. In this study, biodegradable extended nanocomposites based on poly(lactic acid) (PLA)/expanded graphite (EG) were prepared by melt-compounding using a co-rotating twin-screw extruder. Effects of EG loading, aspect ratio, delamination and dispersion state on the mechanical and thermo-mechanical properties of PLA/EG nanocomposites were investigated. Adding the largest EG (EGL) nanoplatelets, having the average particle size of 48.2 µm and aspect ratio of 19.5, to the PLA matrix enhanced the Young modulus, tensile strength, ultimate strain and tensile toughness of the extended PLA sample with benzoyl peroxide (BP) between 40-100%. The observed enhancements originated from restricted PLA molecular motions, assisted PLA crystallization and intensified BP activity in extending the PLA chains. In contrast, EG nanofiller (EGS), with the lowest aspect ratio and size, lowered the PLA relaxation time and accelerated the PLA crystallization. This type of EG showed the weakest reinforcing effect on PLA. For the EG type (EGM) with an intermediate size and aspect ratio, it was observed that the presence of the nanoparticles had a negligible effect on the PLA molecular dynamic and reduced the PLA crystallization rate. The highest impact strength was observed for the PLA/EGM nanocomposite at 1 phr loading.

An insight into different phenomena involved in continuous extrusion foaming of biodegradable poly(lactic acid)/expanded graphite nanocomposites.

The continuous extrusion foaming of poly(lactic acid) (PLA) has several critical drawbacks that crucially limit the substitution of the renewable foams for the extruded foams based on synthetic plastics. In this work, the foamability of PLA melt through a twin-screw extrusion process was improved by using expanded graphite (EG) nanoplatelets having different aspect ratios and loadings along with an organic peroxide. Morphological observations demonstrated the beneficial influences of adding nanofiller, which resulted in the formation of microcellular foams with larger void content and cell densities. Different phenomena, which are involved in the extrusion foaming of PLA melt, are considerably affected by the presence of EG including rheological behavior, PLA crystallization, thermal chain scission of the matrix, chain extension function of the peroxide and thermal decomposition of foaming agent. To correlate the phenomena affected by EG nanofiller with foam morphology, the linear viscoelastic responses, molecular weight, crystallization kinetics and structural properties of PLA and PLA/EG nanocomposites were evaluated.

Intelligent superabsorbents based on a xanthan gum/poly (acrylic acid) semi-interpenetrating polymer network for application in drug delivery systems.

In the present study, semi-interpenetrating polymer networks (semi-IPNs) were synthesized based on crosslinked acrylic acid (AA)/xanthan gum (XG) biopolymer in the presence of N, N'-hexane-1, 6-dilbisprop-2-enamide (MS) or 1,4-butandioldimethacrylate (BDOD) as the cross-linking agent. MS is a novel acrylic-urethane diene monomer prepared through the condensation reaction between AA and hexamethylene diisocyanate (HDI). Scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), proton nuclear magnetic resonance spectroscopy (1H NMR), X-ray diffraction (XRD) and thermogravimetric (TGA) analyses were used to study the morphology, structure and thermal stability of MS and semi-IPNs. The effect of crosslinking agent type on different behaviors such as morphology, stability, swelling, and water-retention capabilities of the synthesized hydrogels were investigated. XG-PAA semi-IPNs exhibited a very high adsorption potential and stability. Hydrogel biocompatibility was confirmed by the outcomes of MTT assay and cell staining. We recommend XG-PAA semi-IPNs as an environmentally benign and readily non-toxic material with an excellent adsorption capacity for application in drug delivery systems, wound healing and dye removal.