Mrinal Bhattacharya

Properties of injection moulded blends of starch and modified biodegradable polyesters

Abstract The properties of blends of starch and aliphatic biodegradable polyesters are presented in this paper. The aliphatic polyesters used include: polye-caprolactone, polybutylene succinate and a butanediol–adipate–terephthalate copolymer. To improve the compatibility between the starch and the synthetic polyester, a compatibilizer containing an anhydride functional group incorporated on to the polyester backbone was used. The blends were melt compounded using a twin-screw extruder. The concentration of the starch in the blend was varied from 10% to 70% by weight. The amylopectin content of the starches varied from 30% to 99%. The addition of a small amount of compatibilizer increased the strength significantly over the uncompatibilized blend. For the compatibilized blend, the tensile strength was invariant with starch content when compared to the original polyester, while it decreased with increase in starch content for the uncompatibilized blend. Blends displayed a sharp intake of water and those containing butanediol–adipate–terephthalate copolymer had a higher water absorption than those containing the other polyester. Each blend displayed two glass transition; one corresponding to the polyester and the other corresponding to starch. For compatibilized blends, the glass transition temperature of starch in the blend is lower than that observed for the uncompatibilized blend. For all polyester blends, those containing 99% amylopectin starch at 70% level had the lowest crystallinity which otherwise decreased with decreased amylopectin level in the starch. Blend morphology indicates that the starch phase become finer as the amylopectin in the blend increased. Also, a higher starch content led to greater melting of the starch granules and at 70% starch by weight, a cocontinuous phase between the starch and the synthetic polymer exists.

Functionalization of polyesters with maleic anhydride by reactive extrusion

Maleic anhydride (MAn) was grafted onto aliphatic and aromatic/aliphatic copolyesters by reactive extrusion in the presence of a free radical initiator using a twin-screw extruder. The grafting reaction was confirmed by spectroscopic analyses. The presence of succinic anhydride groups was shown by FT-IR spectroscopy, and NMR spectra indicate that the grafts consist of single succinic anhydride units. The 2D 1H-NMR spectra (COSY) indicate that grafting reactions take place at aliphatic dicarboxylic acid units of copolyesters. The graft content was determined by a nonaqueous titration method. The effects of concentration of initiator and monomer and reaction temperature on the graft content and intrinsic viscosity were studied. The low percentage grafting in poly(lactic acid) was observed due to the presence of limited free radical sites in the polymer backbone. Temperature and monomer and initiator concentrations affect the graft content, and the desired graft content with minimal degradation can be obtained by controlling these factors.

DYNAMIC RHEOLOGICAL MEASUREMENTS AND ANALYSIS OF STARCH GELS

Abstract The effect of starch modification and concentration on the dynamic shear properties of starch gels in water was studied. The four types of starches used were native corn starch, medium hydroxypropylated distarch phosphate, highly hydroxypropylated distarch phosphate, and distarch phosphate. Concentrations of 4, 6, 8, and 10% (w/w) in distilled water were used for each starch type. All starches showed viscoelastic solid behavior at higher concentrations (6–10% w/w). Critical gelling concentrations were found to be 4, 4, 6, and 6% for native corn starch, medium hydroxypropylated distarch phosphate, highly hydroxypropylated distarch phosphate, and distarch phosphate, respectively. Dynamic measurements were performed to study the effect of concentration and the extent of modification on starch gel properties. The linear viscoelastic region for each type of starch was determined using dynamic strain sweep. Both the elastic and viscous modulus showed only slight dependence upon frequency. The starch gels were classified as weak gels on the basis of their mechanical spectra. Viscous moduli ( G ″) showed a higher dependence upon frequency compared to elastic moduli ( G ′) for all starch types. Equilibrium shear moduli ( G e ) were determined by extending the spectra to zero frequency. Increasing concentration increased the values of G e . Fractional differential model (FDM) was used to model the frequency dependence of the gels. A higher degree of cross-linking resulted in a more shear-resistant gel.

Melt-based compression-molded scaffolds from chitosan-polyester blends and composites: Morphology and mechanical properties

Blends of chitosan and synthetic aliphatic polyesters (polybutylene succinate, polybutylene succinate adipate, polycaprolactone, and polybutylene terepthalate adipate) were compounded with and without hydroxyapatite, a bioactive mineral filler known to enhance osteoconduction. The blends and composites were compression molded with two different granulometric salt sizes (63-125 microm and 250-500 microm) having different levels of salt content (60, 70, and 80%) by weight. By leaching the salt particles, it was possible to produce porous scaffolds with distinct morphologies. The relationship between scaffold morphology and mechanical properties was evaluated using scanning electron microscopy, microcomputed tomography, compression testing, differential scanning calorimetry, small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering. The produced scaffolds are characterized by having different morphologies depending on the average particle size and the amount of NaCl used. Specimens with higher porosity level have a less organized pore structure but increased interconnectivity of the pores. The stress-strain curve under compression displayed a linear elasticity followed by a plateau whose characteristics depend on the scaffold polymer composition. A decrease in the salt particle size used to create the porosity caused in general a decrease in the mechanical properties of the foams. Composites with hydroxyapatite had a sharp reduction in yield stress, modulus, and strain at break. The melting temperature decreased with increased chitosan content. SAXS results indicate no preferential crystalline orientation in the scaffolds. Cytotoxicity evaluation were carried out using standard tests (accordingly to ISO/EN 10993 part 5 guidelines), namely MTS test with a 24-h extraction period, revealing that L929 cells had comparable metabolic activities to that obtained for the negative control.

Osteogenic Differentiation of Human Bone Marrow Mesenchymal Stem Cells Seeded on Melt Based Chitosan Scaffolds for Bone Tissue Engineering Applications

The purpose of this study was to evaluate the growth patterns and osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs) when seeded onto new biodegradable chitosan/polyester scaffolds. Scaffolds were obtained by melt blending chitosan with poly(butylene succinate) in a proportion of 50% (wt) each and further used to produce a fiber mesh scaffold. hBMSCs were seeded on those structures and cultured for 3 weeks under osteogenic conditions. Cells were able to reduce MTS and demonstrated increasing metabolic rates over time. SEM observations showed cell colonization at the surface as well as within the scaffolds. The presence of mineralized extracellular matrix (ECM) was successfully demonstrated by peaks corresponding to calcium and phosphorus elements detected in the EDS analysis. A further confirmation was obtained when carbonate and phosphate group peaks were identified in Fourier Transformed Infrared (FTIR) spectra. Moreover, by reverse transcriptase (RT)-PCR analysis, it was observed the expression of osteogenic gene markers, namely, Runt related transcription factor 2 (Runx2), type 1 collagen, bone sialoprotein (BSP), and osteocalcin. Chitosan-PBS (Ch-PBS) biodegradable scaffolds support the proliferation and osteogenic differentiation of hBMSCs cultured at their surface in vitro, enabling future in vivo testing for the development of bone tissue engineering therapies.

Properties of reactively blended soy protein and modified polyesters

The compatibilizing effect of anhydride groups attached to a polyester was examined while blending soy protein and a biodegradable polyester. Three different polyesters grafted with anhydride functional groups were used as compatibilizers for blending with soy protein concentrate, soy flour, and soy isolate. The processing conditions for these blends in a twin screw extruder and injection-molding machine were evaluated and the physical and mechanical properties of these blends were determined. The concentrations of soy protein and compatibilizer were varied to achieve optimum mechanical properties, exploring the various limits of operating conditions. The dynamic mechanical properties were determined using a rheometric mechanical spectrometer (RMS-800). The enthalpy of fusion was determined using a differential scanning calorimeter. Blends containing compatibilizer gave enhanced tensile strength when compared to blends without compatibilizer. The morphology of these blends was investigated with the help of an optical microscope and X-ray diffraction was used for crystallinity studies. Water and oil absorption by these blends were determined for a period of 25 days. © 1999 Society of Chemical Industry

Polymer Nanocomposites—A Comparison between Carbon Nanotubes, Graphene, and Clay as Nanofillers

Nanofilled polymeric matrices have demonstrated remarkable mechanical, electrical, and thermal properties. In this article we review the processing of carbon nanotube, graphene, and clay montmorillonite platelet as potential nanofillers to form nanocomposites. The various functionalization techniques of modifying the nanofillers to enable interaction with polymers are summarized. The importance of filler dispersion in the polymeric matrix is highlighted. Finally, the challenges and future outlook for nanofilled polymeric composites are presented.

Transient temperature and velocity profiles in a canned non-Newtonian liquid food during sterilization in a still-cook retort

Abstract Natural convection heating of a canned liquid food during sterilization is simulated by solving the governing equations for continuity, momentum and energy conservation for an axisymmetric case, using a finite element code. The model liquid has constant properties except viscosity (temperature dependent and shear thinning) and density (Boussinesq approximation). The velocity field establishes itself much more rapidly than the temperature field. The maximum axial velocity is of the order of 10 −4 m s −1 because of low Grashof number. The coldest point is not fixed but migrates in a region that is 10–12% of the can height from the bottom of the can and at a radial distance approximately one-half of the radius. On the basis of the computed particle path it appears that the liquid initially located just below the top center is exposed to the minimum heat treatment and should be of most concern in the thermal process calculations.

Synthesis and characterization of anhydride-functional polycaprolactone

Polycaprolactone-graft-maleic anhydride (PCL-g-MA) copolymer was prepared by grafting maleic anhydride onto PCL in a batch mixer and in an extruder using dicumyl peroxide as the initiator. The graft content was determined with the volumetric method by converting the anhydride functions to acid groups and then titrating with ethanolic potassium hydroxide. The grafted polymer was extracted with xylene to remove any unreacted monomer before the estimation step. The effect of temperature and the various concentrations of the initiator and monomer used for the grafting reaction were investigated. The presence of residual initiator in the reaction product was checked using thin-layer chromatography. Molecular weight determination was carried out for the pure and grafted polymer using gel permeation chromatography to determine if chain scission was present. Results indicate that maleic anhydride is grafted onto PCL using free radical initiators. The grafting reaction was confirmed by FTIR and NMR techniques. FTIR spectra showed absorption bands around 1785 and 1858 cm−1. NMR spectra gave signals for methine proton at 3.47 ppm. For a given peroxide level, a higher temperature or residence (reaction) time gave higher percentage of grafted MA. There was an optimum temperature and initiator concentration after which the percentage of MA grafted on PCL decreased. The number-average molecular weight, tensile strength, and the percent elongation of PCL-g-MA were comparable to those of PCL before grafting.

Effect of processing conditions on the dynamic mechanical properties of starch and anhydride functional polymer blends

Abstract Reactive blending of starch with ethylene-propylene-g-maleic anhydride (EPMA) and styrene maleic anhydride (SMA) copolymers was carried out in a batch mixer. The effect of processing conditions, such as mixer speed and mixing time, on the dynamic mechanical properties and morphology, was studied. Starch/EPMA blends showed two distinct glass transitions in the G′ and G″ plots, one corresponding to the starch and the other corresponding to EPMA. Starch/SMA blends exhibited one broad transition, since the glass transition temperatures of starch and SMA were in close proximity to one another. The starch in the blend was sensitive to the processing conditions used in this study. Increasing the mixing time from 10 to 20 min and increasing mixing speed from 50 to 100 rev min−1 resulted in increased melting of starch granules. Increasing the mixing speed and mixing time also resulted in increased degradation of starch, as evident from the gel permeation chromatography.