All issues / Volume 2 (2008) / Issue 3 (March)
Propylene homo- and copolymers (both random and block types) with and without beta nucleation were injection moulded and the related plaques joined by linear vibration welding. The melt flow index (MFI) of the polypropylenes was different. During vibration welding the pressure has been varied (0.5, 2 and 8 MPa). The properties of the welded plaques were determined under both static (tensile) and dynamic conditions (Charpy impact). It was found that the mechanical performance of the welds could strongly be improved when beta nucleated PP plaques were combined with each other. In other combinations the ‘weaker’ alpha modification controls the mechanical response. The supermolecular structure of the weld was assessed by polarised light microscopy using thin microtomed sections. Formations of the weld morphology along with its effects on the mechanical performance were discussed.
The viscoelastic properties of an ethylene/propylene/diene rubber (EPDM) containing 30 parts per hundred parts rubber [phr] carbon black (CB) were determined by dynamic mechanical thermal analysis (DMTA) measurements. A 15-term Maxwell-model was created to describe the time-dependent material behavior of this rubber. The frictional behavior under dry rolling conditions was studied on a home-built rolling ball (steel)-on-plate (rubber) (RBOP) test rig. Both normal and tangential forces were detected during the measurements. The rolling test was simulated with the MSC.Marc finite element (FE) software using the evaluated viscoelastic material properties. Results of the experimental tests and of the simulation were compared and a good agreement was found between them.
Stimuli-responsive poly(ampholyte)s containing L-histidine residues: synthesis and protonation thermodynamics of methacrylic polymers in the free and in the cross-linked gel forms
M. Casolaro, Y. Ito, T. Ishii, S. Bottari, F. Samperi, R. Mendichi
Vol. 2., No.3., Pages 165-183, 2008
Vol. 2., No.3., Pages 165-183, 2008
Methacrylate-structured poly(ampholyte)s were synthesized in the homopolymer and copolymer forms starting from the N-methacryloyl-L-histidine (MHist) and the N-isopropylacrylamide (NIPAAm). They were also obtained in the cross-linked (hydrogel) form, showing a close thermodynamic behaviour as that shown by the corresponding soluble free polymer analogues. Viscometric data revealed that the minimum hydrodynamic volume of the polymer at its isoelectric point (pH 5) shifted to lower pHs as the NIPAAm content increased, and beyond a critical low MHist content the reduced viscosity decreased, even at low pHs. The phenomenon was attributed to hydrophobic forces between the isopropyl groups outweighing the repulsive electrostatic interactions of the polymer in the positively charged form. A similar behaviour was shown by the corresponding hydrogel. The latter also revealed a different phase transition phenomenon induced by external stimuli (temperature, pH, ionic strength, electric current) when compared to the acrylate-structured analogues. The polyMHist, as well as the corresponding monomer, was found for two days to be non toxic against the mouse osteoblasts (MC3T3-E1).
Lactic acid and &Summa;-caprolactone based polymers and their derivates are widely used in biomedical applications. Different properties are introduced by modifying the composition. In this study, poly(ε-caprolactone/D,L-lactide)-b-poly(ε-caprolactone) multiblock copolymers were synthesized as poly(ester-urethane)s (PEUs) by polymerizing in two steps involving ring-opening polymerization of precursors and by diisocyanate linking of precursors to produce thermoplastic elastomers (TPEs). The precursors and products were characterized by SEC, 1H-NMR and DSC, and dynamic mechanical study (by dynamic mechanical analysis, DMA) as well as morphological characterization (by transmission electron microscopy, TEM) of the product TPEs was carried out. Tensile and creep recovery properties of them were also studied. According to the characterizations, all the polymerizations were successful, and the prepared TPEs showed clear elastic behavior. In the DMA scans, rubbery plateau in the storage modulus curves between Tg and terminal flow region was clearly detectable indicating elasticity. The TEM images demonstrated phase separation of amorphous and crystalline blocks when the degree of crystallinity of the hard blocks was high enough. The elongations of TPEs varied between 800–1800%, while the modulus was 7–66 MPa. Two different types of recovery tests indicated the creep properties of TPEs to be highly dependent on the degree of crystallinity.
The rigid polyurethane foams (RPUFs) have been fabricated from high functional crude 4,4’-di-phenylmethane diisocyanate (CMDI) and polypropylene glycols (PPGs) for a wide range of surfactant concentration with an environmently friendly blowing agent (HFC 365mfc). Cream time, gel time, and tack-free time increased with the addition of surfactant. Foam density decreased rapidly to a minimum at 0.5 pphp (part per hundred polyol) surfactant due to the increased blowing efficiency with surfactant. Surface tension rapidly decreased to an asymptotic value at 2 pphp surfactant. In accordance with this, cell size decreased and closed cell content increased rapidly to constant values at low surfactant concentrations (<1 pphp). The decrease of cell size was accompanied by the decrease of thermal conductivity to give a linear relatiohship between the two implying that the series model of heat transfer is applicable.
In the present study polyacrylamide (PAm)-gelatin-hydroxyapatite (HA) composites have been synthesized by suspension polymerization method. The prepared composites were characterized by Fourier transform spectroscopy (FTIR) which revealed the presence of functional groups in the composite. The X-ray diffraction (XRD) studies indicated that HA powder was present in nano size. Thermogravimetric analysis (TGA) revealed that composite is more thermally stable than the polymer matrix alone. The morphology of composite studied by optical microscopy (OPM) and scanning electron microscopy (SEM) suggested that pore size was between 3–20 µm. The composites showed adequately good mechanical properties as evident from the varying compressive strength and modulus in the range 31.57±8.16 MPa and 745±388 MPa, respectively. The water sorption behavior was found to be dependent on the chemical composition of the matrix and the sorption data were used to calculate network parameters. The porosity of composite varied between 4 to 30.66%.The in vitro blood compatibility indicated that the adsorption of bovine serum albumin (BSA) varied from 0.11 to 0.24 mg•g–1, the percentage haemolysis was between 2.4 to 6.9% and the weight of blood clot formed on the composite surfaces were found in the range 11 to 52 mg.
Asymmetric and semi-symmetric amphiphilic diblock copolymers polystyrene-block-poly (dimethylaminoethyl methacrylate) (PS-b-PDMAEMA) with the same PS block length of 62 repeat units and quite short (3 repeat units) or equivalent (47 repeat units) length of PDMAEMA have been prepared simply by varying the ratio of the bromine-terminated macroinitiator polystyrene (PS-Br) to DMAEMA using atom transfer radical polymerization (ATRP). The chemical structures and compositions of the PS-b-PDMAEMA block copolymers are studied by nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC), and elementary analysis (EA). The self-assembly behaviors of copolymers in N,N-dimethyl formamide (DMF) with different pH and dioxane/water binary solvent mixture by direct dissolution method (DD), are studied by transmission electron microscopy (TEM), electron diffracting analysis (EDA), and energy-dispersive analysis of X-rays (EDAX) techniques. Transmission electron microscopy results suggest that asymmetric block copolymer PS62-b-PDMAEMA3 (the numbers in the form of footnotes represent repeated units of each monomer in the copolymer) can form spherical core-shell micelles, large compound reverse micelles (LCRMs), hexagonal/rhombic phases, reverse hexagonal/rhombic phases, vesicles, reverse vesicles and necklace-like reverse micelles, controlled by common or selective solvent and pH, while most of the aggregates of semi-symmetric PS62-b-PDMAEMA47 are simply spherical, such as spherical core-shell micelles and reverse spherical core-shell micelles, besides hexagonal/rhombic phases. All above structures are controlled by three components of the free energy of aggregation: core-chain stretching, interfacial energy and intercoronal chain interaction.
Novel thermoplastic vulcanizates (TPVs) based on polypropylene (PP) and new generation ethylene-octene copolymer (EOC) have been developed by dynamic vulcanization process, which involves melt-mixing and simultaneously crosslinking a rubber with a thermoplastic. In this paper technologically compatibilized blends of PP and EOC were dynamically vulcanized by coagent assisted peroxide crosslinking system. The effect of structurally different types of peroxides, namely dicumyl peroxide, di-tert butyl peroxy isopropyl benzene and tert-butyl cumyl peroxide with varying concentrations on the properties on TPVs was mainly studied. The physico-mechanical, thermal and morphological properties of these TPVs were characterized by using X-ray diffraction (XRD), differential scanning calorimeter (DSC) and scanning electron microscopy (SEM).