Iranian polymer journal
Volume:21 Issue: 2, 2012

Effect of the blend ratios on the morphology and melt rheology of poly(lactic acid) (PLA)/poly(butylene succinate adipate) (PBSA) blends were investigated using scanning electron microscope, strain-controlled rheometer, and capillary rheometer techniques. The morphological analysis shows that the average radius of the dispersed droplets of PBSA particles increases with change in the blend composition, and a co-continuous structure was generated when PBSA content reached 40%. For the linear viscoelasticity, the increase in the storage modulus at low-frequency region was more distinct in PLA/PBSA blends than in their pure components. A second plateau is clearly observed when the PBSA content was 20% or higher. Weight relaxation spectra showed that there was a longer relaxation time for blend system. These relaxation times were considered to be the shape relaxation periods of the droplets, which increase with change in the blend composition. The interfacial tensions of the PLA/PBSA blends at different compositions were between 5.3 and 6.1 mN/m, calculated from the weighted relaxation spectra and slightly higher than those obtained from Palierne model. These values are relatively high, indicating the poor miscibility of the two polymers. Both pure PLA and PBSA follow the Cox–Merz rule, in good manner. Though, the rule does not satisfy with the PLA/PBSA blends. In addition, PLA/PBSA blends show more non-Newtonian tendencies than their pure components.

In order to improve the toughness of glass fiber (GF) reinforced unsaturated polyester resin (UPR), low molecular weight polyisobutylene (LPIB) was selected as the toughening agent. Considering its poor thermal compatibility with UPR matrix, LPIB was first grafted by two small molecular compounds, named maleic anhydride (MAH) and glycidyl methacrylate (GMA) through the novel solvothermal method which was developed in our laboratory. And then, all of these three kinds of low modulus elastomers, including LPIB, MAH grafted polyisobutylene (LPIB-g-MAH) and GMA grafted polyisobutylene (LPIB-g-GMA) were selected to modify GF reinforced UPR (GFRUP) composites. According to the results, incorporation of small amounts of grafted LPIB contributed greatly to the improvement of the toughness of GFRUP composites because of the high flexibility of the molecular chain without obviously influencing other primary properties. Moreover, 4 wt% of elastomer was an optimal amount for promoting the mechanical properties of GFRUP composite. Compared to other liquid rubbers, LPIB-g-GMA had the best toughening effect due to its stronger effect of GMA on UPRGF system. In addition, the impact strength of the modified GFRUP composite was improved up to 2.3 order of that of the unmodified GFRUP composites when 4 wt% LPIB-g-GMA was added. Consequently, LPIB-g-GMA could be employed as an effective toughening agent to GFRUP system. The toughening mechanism, thermal behavior, thermal stability and morphology of GFRUP composite are also discussed. The morphology analysis further proved the increase in toughness through the addition of grafted LPIB.

Alginate and chitosan nanoparticles were prepared using a new reverse micelle system, composed of cetyltrimethylammonium bromide (CTAB) as a surfactant, isooctane as a solvent, and 1-hexananol as a co-solvent. The obtained nanoparticles were characterized by FTIR, DLS and TEM techniques. The main objective of this study was to investigate the effects of polymer concentration, water content, and volumetric ratio of co-solvent to solvent on the physical and morphological properties of the prepared nanoparticles. To evaluate the results, the design of experimental was initially carried out and then the obtained data were statistically analyzed using the Qualitek-4® software. Results revealed that the size of the prepared alginate and chitosan nanoparticles varied in the range 220–490 and 210–1,050 nm, respectively. Furthermore, increasing either alginate or chitosan concentration increased the size of their nanoparticles. The results also showed that the size of nanoparticles was decreased with increasing the volumetric ratio of co-solvent/solvent. Finally, the size of alginate nanoparticles was increased by increasing the water content while it decreased the size of chitosan nanoparticles. Considering the statistical analysis of experiments, the polymer concentration is the major parameter affecting nanoparticles’ size. In contrast, water content has the smallest effect on the size of nanoparticles. However, the difference between the particle sizes of chitosan and alginate nanoparticles cab be attributed to the electrostatic repulsion between chitosan and CTAB.

In this study, we have prepared a series of novel biodegradable polymer [polylactide (PLA)]-based nanocomposites using graphite nanosheets (GNs) and multi-walled carbon nanotubes (MWCNTs) by solution-blending technique and investigated their morphologies, structures, thermal stabilities, mechanical and dielectric properties, and electrical and thermal conductivities. Before preparation of the PLA/GNs/MWCNTs nanocomposites, the raw GNs used were endured a rapid expansion by thermal treatment. Temperature of this treatment had some obvious impacts on morphological changes of graphite nanosheets which were verified by means of scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. Resultant nanocomposites were characterized and evaluated by means of SEM, XRD, thermal conductivity measurements, tensile and impact tests, thermogravimetric analysis and dielectric measurements. Results obtained in this study indicated that thermal-expanded GNs in the presence of MWCNTs facilitate the formation of an appropriate conductive network in PLA matrix which resulted in a relatively low percolation threshold for thermal and electrical conductions of PLA/GNs/MWCNTs nanocomposites. Significant improvements in thermal and electrical conductivities, thermal stability and mechanical properties of PLA/GNs/MWCNTs nanocomposites obtained through the presence of both nanoparticles in PLA matrix were associated with their good co-dispersion and co-reinforcement effects. The macroscopic properties of nanocomposites were found to be strongly dependent on their components, concentrations, dispersion, and the resulted morphological structures.

Three types of surfactants were used to enhance the dispersion of multi-wall carbon nanotubes (MWCNTs) in the epoxy matrix. MWCNTs were separately treated with non-ionic (polyoxyethylene octyl phenyl ether, Triton X-100), cationic (hexadecyl-trimethyl-ammonium bromide, CTAB) and anionic (sodium dodecyl sulfate, SDS) surfactants and their effects were evaluated on the dispersion state and surface chemistry, as well as on the tensile properties and tensile fracture surface morphology of MWCNTs/epoxy nanocomposites. The active surfaces of the carbon nanotubes were characterized by FTIR. The non-ionic surfactant, Triton X-100, had the best effect on dispersion of the MWCNT in the epoxy matrix, thus, positively affecting the tensile parameters of the corresponding nanocomposites which were attributed to the “bridging” effects between the MWCNT and epoxy, introduced by the hydrophobic and hydrophilic heads of the corresponding surfactant. Presence of MWCNTs as reinforcing agent increased the elastic modulus of nanocomposites, indicating the improved interfacial adhesion between CNTs and polymer matrix. The regions of nucleation and propagation of cracks were clearly seen in the SEM micrographs of the tensile fracture surface of the nanocomposites. The cracks deviated on reaching the carbon nanotubes. The dispersing aiding capabilities of the three surfactants used in the present study were as follows: cationic < anionic < non-ionic.

In chemical oxidative homopolymerization of aniline-N-propanesulfonic acid, ammonium persulfate has been used as an oxidant to obtain water-soluble and self-acid-doped polyanilines. Copolymerization of aniline-N-propanesulfonic acid with aniline, using three feed molar ratios of comonomers has been studied, as well. The polymers and copolymers had moderate molecular weights and were soluble in water and polar solvents. They have been obtained in self-acid-doped form, as has been evidenced by UV–Vis spectroscopy, as green-colored materials, and can be de-doped with alkaline solutions. The propanesulfonic groups had not cleaved during the oxidative polymerization and the atomic ratio between nitrogen and sulfur atoms (N/S) was determined by X-ray photoelectron spectroscopy which was consistent with the chemical structure. The chemical structures and morphologies of the homo- and copolymers have been studied by FTIR, 1HNMR, UV–Vis, thermogravimetric analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction methods. The X-ray diffraction patterns of the homo- and copolymers have showed a high degree of crystallinity which can be explained by the ionic interaction between propanesulfonate anions and the amine nitrogen atoms of the main chain, resulting in the layering structure of the polyaniline chains. Electrical conductivity of the homopolymer determined at room temperature on pressed pellet was 0.0038 S/cm, while the copolymers show higher conductivities compared with homopolymer.