Jin San Yoon

Miscibility of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(vinyl chloride) blends

Abstract The miscibility behaviour of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-HV) blended with poly(vinyl chloride) (PVC) was investigated by using differential scanning calorimetry, dynamic mechanical thermal analysis, Fourier-transform infra-red spectroscopy and a mechanical testing system. A blend of PHB-HV containing 8% HV (PHB-8HV) with PVC was immiscible, showing two separate Tg values in all compositions: whereas a blend of PHB-HV containing 18% HV (PHB-18HV) with PVC was miscible, showing a melting-point depression and a single Tg in the whole range of compositions. For the PHB-18HV/PVC system, the C-O-C stretching vibration at 1183 cm−1 of PHB-18HV and the CHCl deformation at 1254cm−1 of PVC were shifted, indicating that there exists a specific intermolecular interaction between the two components. In addition, as the PVC component was increased, tensile strength and Youngs modulus were increased, while the inverse behaviour was observed in elongation at break.

Miscibility of poly-d(−)(3-hydroxybutyrate) in poly(ethylene oxide) and poly(methyl methacrylate)

Abstract Miscibility behaviour of poly- d (−)(3-hydroxybutyrate) (PHB)/poly(ethylene oxide) (PEO) and PHB/poly(methyl methacrylate) (PMMA) blends were studied using differential scanning calorimetry and the vapour sorption technique. The PHB/PEO system showed a single glass transition, whereas two glass transitions were observed for the PHB/PMMA system over the entire range of composition tested. The addition of PEO, which has been reported to be miscibile with PHB as well as PMMA, did not enhance the compatibility of PHB and PMMA. Polymer polymer interaction parameters obtained by the chloroform vapour sorption technique were found to be negative for PHB/PEO and positive for PHB/PMMA systems. However, the interaction parameters of both systems change significantly with composition.

Preparation and characterization of electrospun poly( l -lactic acid- co -succinic acid- co -1,4-butane diol) fibrous membranes

Poly(l-lactic acid-co-succinic acid-co-1,4-butane diol) (PLASB) was synthesized by direct condensation copolymerization ofl-lactic acid (LA), succinic acid (SA), and 1,4-butanediol (BD) in the bulk using titanium(IV) butoxide as a catalyst. The weight-average molecular weight of PLASB was 2.1 × 105 when the contents of SA and BD were each 0.5 mol/100 mol of LA. Electrospinning was used to fabricate porous membranes from this newly synthesized bioabsorbable PLASB dissolved in mixed solvents of methylene chloride and dimethylformamide. Scanning electron microscopy (SEM) images indicated that the fiber diameters and nanostructured morphologies of the electrospun membranes depended on the processing parameters, such as the solvent ratio and the polymer concentration. By adjusting both the solvent mixture ratio and the polymer concentration, we could fabricate uniform nanofiber non-woven membranes. Cell proliferation on the electrospun porous PLASB membranes was evaluated using mouse fibroblast cells; we compare these results with those of the cell responses on bulk PLASB films.

Preparation of Biodegradable Nanocomposites by Incorporation of Functionalized Carbon Nanotubes

Polymeric carbon nanotube composites constitute one of the most promising alternatives to conventional filled polymers. The dispersion of nanometer-sized carbon nanotubes in a polymer matrix markedly improves its physical properties. This approach can also be applied to biodegradable synthetic aliphatic polyesters such as poly(L-lactic acid) (PLLA), which has been receiving an increasing amount of attention due to environmental concerns. In this study, the mechanical properties of PLLA were enhanced by the incorporation of a small amount of carbon nanotubes (0.8 wt%) in the solution state, which could make this material a good competitor for commodity materials such as general purpose plastics, while allowing it to retain its biodegradability. In order to obtain a homogeneous dispersion of the carbon nanotubes in the matrix, oxygen-containing groups were introduced on the surface of the MWNTs. The good dispersion of the nanotubes in the PLLA matrix observed by scanning electron microscopy was attributed to the fact that the PLLA was compatible with the functionalized MWNTs during the compounding process. The electrical conductivity of the composites was also investigated.

Alternating copolymers as compatibilizer for blends of poly(ethylene terephthalate) and polystyrene

Compatibilization of blends of poly(ethylene terephthalate) (PET) and polystyrene with alternating copolymers of maleic anhydride and isobutylene (IM) and its partly phenol substituted product (PIM) has been studied. The characterization techniques applied were dynamic mechanical analysis, differential scanning calorimetry, scanning electron microscopy, and tensile testing. In all compositions studied, morphological observations demonstrated that the addition of approximately 5 wt % of copolymers led to the domain size reduction of dispersants. The PIM copolymer was most effective in reducing the domain size, whereas the IM copolymer was less satisfactory. The blends containing PIM also gave the more enhanced ultimate strength than those of other systems. The noncrystalline PIM copolymers lowered the tensile modulus of the blend as much as 60% even in the polystyrene-rich region and varied linearly with values of quenched PET modulus throughout the compositions, indicating the formation of homogeneous amorphous phase. Based on the experimental observation that the reduced domain size with PIM copolymer, a compatibilization mechanism of the blend with PIM alternating copolymer is proposed and discussed in terms of the interactions between ester groups of PET and PIM (transesterification), and the possible formation of intermediate π-complex between the π-electron deficient aromatic ring of PIM and π-electron rich aromatic ring of PS.

Characterization of Polycarbonate/Multiwalled Carbon Nanotube Composites

Polycarbonate/multiwalled carbon nanotubes (PC/MWNT) nanocomposites with different contents of MWNT were successfully prepared by melt compounding. The mechanical properties of the PC/MWNT nanocomposites were effectively increased due to the incorporation of MWNTs. The composites were characterized using scanning electron microscopy in order to obtain the information on the dispersion of MWNT in the polymeric matrix. In case of 0.3 wt% of MWNT in the matrix, strength and modulus of the composite increased by 30% and 20%, respectively. In addition, the dispersion of MWNTs in the PC matrix resulted in substantial decrease in the electrical resistivity of the composites as the MWNTs loading was increased from 1.0 wt% to 1.5 wt%.

Isothermal foam growth in polymer matrices

Abstract A theoretical model is discussed to analyze the growth kinetics of gas bubbles in isothermal viscous polymer solutions. This model obtained by grafting the Tri Diagonal Matrix Algorithm (Patankar, Ref. [1]) into the cell model (Amon and Denson, Ref. [2]), eliminates many of the assumptions introduced in the previously reported mathematical models. Neglect of the convection term in the transient diffusion equation results in significant error in the prediction of the bubble growth. Assumption that diffusion of volatile solute is confined within a thin layer around the gas-liquid interface is also proved to be unrealistic when diffusion coefficient is relatively high. Physical parameters for expansion of nitrogen bubbles in vinylidene chloride-acrylonitrile copolymer at 100° (Barlow and Langlois, Ref. [3]) are taken to investigate the applicability of the model. Effect of initial bubble size on the growth behavior lasts a long time. Increase of diffusion coefficient and decrease of external pressure and viscosity of polymer solution enhance greatly the rate of bubble growth, whereas surface tension affects it only slightly.

Preparation and Characterization of Multiwalled Carbon Nanotube/Poly(ε-Caprolactone) Composites via In Situ Polymerization

Poly(ε-caprolactone)/multiwalled carbon nanotube (PCL/MWCNT) composites with different MWCNT contents were successfully prepared by in situ bulk polymerization, which could make them good competitors for commodity materials such as general purpose plastics, while allowing them to completely retain their biodegradability. The mechanical properties of the PCL/MWCNT composites were effectively increased due to the incorporation of the MWCNTs. The composites were characterized using scanning electron microscopy, in order to obtain information on the dispersion of the MWCNTs in the polymeric matrix. In the case where 0.5 wt% of MWCNTs were dispersed in the matrix, the strength and modulus of the composite increased by 23% and 71%, respectively. In addition, the dispersion of the MWCNTs in the PCL matrix resulted in a substantial decrease in the electrical resistivity of the composites being observed as the MWCNTs loading was increased from 0 wt% to 0.5 wt%.

Influence of Silicate Surface Modification on Morphology and Mechanical Properties of Nylon6/Clay Nanocomposites

A new method was attempted to improve the interaction between nylon 6 with a commercially available organoclay, Cloisite®25A (C25A) through modification of C25A with 3-aminopropyltriethoxy silane, 3-(trimethoxysilyl)propyl methacrylate, 3-(glycidoxypropyl) trimethoxysilane and 3-isocyanate propyltriethoxy silane. C25A and C25A modified with the silane compounds(TFC) were melt mixed with nylon 6. X-Ray diffraction and transmission electron microscopy images revealed that all the TFC layers were fully exfoliated in nylon 6 matrix irrespectively of the type of the silane compounds used for the modification. Tensile properties of nylon 6 were most significantly improved when 3-(glycidoxypropyl)trimethoxysilane modified C25A was incorporated. The chemical reaction between the epoxy groups and the end groups of nylon 6 raised the interfacial interaction and thus was responsible for the enhanced tensile properties.

Thermal Stability of Poly(ε-caprolactone)/Carbon Nanotube Composites

Poly(ε-caprolactone) (PCL) is expected to have a wide range of applications not only as a biodegradable material but also as a biomedical material, owing to its excellent biocompatibility. The compounding of a small amount of carbon nanotubes (CNTs) frequently produces polymeric composites with markedly improved physical and thermal properties. The dispersion of the nanometer-sized CNTs in the polymer matrix is essential for the enhancement of its properties. In this study, multiwalled carbon nanotubes (MWCNTs) were compounded with the PCL matrix in the solution state using chloroform. The thermal stabilities of the PCL and MWCNT/PCL composites were investigated using the data acquired from the thermogravimetric analysis (TGA). The thermal degradation behavior provides useful information which can be used for the establishment of the optimum processing conditions as well as to identify the potential applications of the materials. The detailed kinetics of the thermal degradation of the composites was investigated by analyzing their thermal behavior at different heating rates in a nitrogen atmosphere. The activation energy of thermal degradation was determined by using the equations proposed by Kissinger and Flynn-Wall-Ozawa. This method was chosen from among the various methods which have been proposed for the evaluation of the non-isothermal kinetic parameters pertaining to the thermal degradation of a polymer. The apparent activation energy of the PCL/MWCNT composite was considerably higher than that of neat PCL.