Modification on crystallization of poly(vinylidene fluoride) (PVDF) by solvent extraction of poly(methyl methacrylate) (PMMA) in PVDF/PMMA blends

The crystallization modification of poly(vinylidene fluoride) (PVDF) was investigated for the blend films of PVDF and poly(methyl methacrylate) (PMMA). The mass crystallinity (χ_c) and further, the β-phase content (F_(β)) of PVDF, were studied for the as-prepared blend films with different mass ratios. In addition, the variations of χ_c and F_(β) were systematically probed once the PMMA component was removed from the related blend systems. DSC, FTIR and XRD measurements all indicated that 1) χ_c, F_(β) and even the content of α-phase (F_(α)) decreased with the addition of PMMA; 2) with the extraction of PMMA, both χ_c and F_(β) increased while F_(α) decreased. It is worth noting that the increase of χ_c and F_(β) depended on the relative amount of extracted PMMA (E_PMMA), i.e., the more PMMA was removed, the more χ_c and F_(β) increased. These results reveal the hindrance effect from the PMMA constituent to the crystallization of PVDF, and consequently, this restriction would be released when the PMMA was extracted.     

Influence of free volume on the mechanical properties of Epoxy/poly (methylmethacrylate) blends

Positron lifetime measurements have been performed to investigate the free volume dependence of the mechanical properties of Epoxy/poly methyl methacrylate (PMMA) blends of varying composition of PMMA (2.5, 5, 7.5, 10, 12.5, 15, and 17.5 wt%). The mechanical properties of the blends have been evaluated according to the (ASTM) standard. The positron results indicate that the mechanical properties like tensile strength and surface hardness have a significant dependence on the free volume of the blends. It is also found that the blends of the present study show positive deviation from the familiar linear additivity rule suggesting the immiscible nature of the blends. Further, up to 5-wt% of PMMA in the blend, an increase in relative fractional free volume correlates well with a decrease of tensile strength.     

Miscible blends from rigid poly(vinyl chloride) and epoxidized natural rubber

Miscible blends of rigid poly(vinyl chloride), PVC, and epoxidized natural rubber (ENR) having 50 mol % epoxidation level, are prepared in a Brabender Plasticorder by the melt-mixing technique. Changes in Brabender torque and temperature, density, dynamic mechanical properties and DSC thermograms of the samples are studied as a function of blend composition. The PVC-ENR blends behave as a compatible system as is evident from the singleT _g observed both in dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The moderate level broadening of theT _g zone in blends is due to microinhomogeneity, which may arise from the particle structures of PVC perturbing the molecular level mixing of PVC and ENR. Scanning electron microscopic studies were conducted on nitric acid-etched samples and the results showed continuous structures of blend components as well as the occurrence of solvent-induced cracks in high PVC blends.     

Synthesis and characterization of films based on cross linked blends of poly (vinylalcohol) and poly (vinylpyrrolidone) with glutaraldehyde for tissue engineering application

In these recent years, polymer blending is one of the significant interests by tissue engineering experts, since blending could produce biomaterials with enhanced physical and biological properties compare to the parent materials. In this context, present study aims at formation and characterization of polymeric blend of poly (vinylalcohol) and poly (vinylpyrrolidone) produced for tissue engineering application. Both polymers are blended at different concentrations to obtain films and nanofibers using solvent casting and electrospinning method respectively. The successful blending is confirmed by Fourier transform infrared spectroscopy, Field emission scanning electron microscope analysis and X‐ray diffraction. Later glutaraldehyde was added to chemically cross link the polymers and its effect was investigated on swelling and solubility properties of the blend. Experimental results reveal a relevant enhancement in the properties of poly (vinylalcohol) and poly (vinylpyrrolidone) blend when glutaraldehyde was added.     

Thermal and elastic properties of poly(vinyl chloride) (PVC) + chlorinated polyethylene (CPE) blends

Eight types of PVC + CPE blends with different weight ratios (PVC/CPE = 100/0, 90/10, 80/20, 60/40, 40/60, 20/80, 10/90, and 0/100) are tested. Data on the heat conductivity, thermal diffusivity, and heat capacity of the blends investigated are reported. Primary attention is paid to the structural approach for effective elastic constants: bulk, shear, and Young's modulae. The blends are considered as random mixtures of two isotropic constituents. It is found that the elastic moduli may be well represented by the Kerner and Budiansky equations.     

Electrical conduction measurements in solution-mixed polyblends of poly(vinylidene fluoride) and poly(methylmethacrylate)

The d.c.-electrical conductivity studies have been done in poly(vinylidene fluoride) (PVDF), poly(methylmethacrylate) (PMMA) and their polyblends in the entire composition range as a function of voltage and temperature. Some studies on thickness and electrode dependence of the electrical conductivity were also carried out. The results obtained show that the charge carriers are generated by Richardson-Schottky emission from the electrode as well as from trapped ionic impurities at high fields and are conducted through the bulk of the material by a carrier hopping process. The values of Schottky field lowering constant _RS, the Poole-Frenkel trap lowering constant _PF, the effective metal insulator potential barrier, the ionic jump distance and the activation energy involved in the conduction process are reported. A.c.-conductivity values were calculated from a.c.-dielectric data and the results show the evidence of hopping conduction in the bulk of polyblends.     

Latex derived blends of poly(vinyl acetate) and natural rubber: thermal and mechanical properties

Poly(vinyl acetate) (PVAc) and natural rubber blends (NR) were prepared by low shear blending of the corresponding lattices. Thin films were cast using a doctor blade technique. SEM and DMA confirmed the essential immiscibility of the two polymers. Even when the poly(vinyl acetate) forms the matrix phase, it still contains domains encapsulated by a rubber phase where particles that resemble the original latex are visible. This incomplete droplet coalescence of the poly(vinyl acetate) is attributed to the fact that the rubber latex droplets were an order of magnitude smaller than the poly(vinyl acetate) latex droplets. Tensile testing revealed a nonlinear dependence of tensile strength and elongation on blend composition. Surprisingly good tensile yield strengths were obtained at intermediate to high PVAc contents. Thermogravimetric analysis of degradation in air and nitrogen atmospheres indicated independent degradation of the parent polymers.     

Electronic properties of polyaniline doped with dodecylbenzenesulphonic acid (PANI-DBSA) and poly(methyl methacrylate) (PMMA) blends in the presence of hydroquinone

Films of polyaniline doped with dodecylbenzenesulphonic acid (DBSA) and poly(methyl methacrylate) (PMMA) blends were studied with and without compatibilising agent “hydroquinone”. Hydroquinone was used to maximize solubility and to make it compatible with polymethylmethacrylate (PMMA) to get uniform and homogenous films on indium tin oxide ITO coated glass. Current density measurement as a function of voltage (J–V) and capacitance voltage (C–V) measurements at different temperature were carried out. The observed J–V and C–V characteristics can be satisfactorily fitted using the modified Schottky equations. The junction parameters were strongly influenced by hydroquinone. From C–V characteristics, the built-in voltage and charge carriers concentration were also calculated and discussed.     

Tear and wear of thermoplastic elastomers from blends of poly(propylene) and ethylene vinyl acetate rubber

Tear and wear properties of thermoplastic elastomers from blends of poly(propylene) (PP) and ethylene vinyl acetate rubber have been studied with special reference to the effect of blend ratios and dynamic crosslinking of the rubber phase. Both tear and wear resistance of the composites were found to increase with increasing proportion of the PP phase. Dynamic crosslinking of the blends containing higher proportions of the rubber phase (> 60%) increases the wear and tear properties, but blends containing higher proportions of the plastic phase show a decrease in properties due to the degradation of the PP phase. Attempts have been made to correlate the changes in properties with the morphology of system. In order to understand the mechanism of failure, the tear and wear fracture surfaces have been examined by scanning electron microscopy. The fractographs have been correlated with the strength and type of failure of these blends.     

Analysis and properties of some commercial poly(methylmethacrylate)-based materials

Four commercial crosslinked poly(methacrylate)-based materials have been analysed, and the differences in some of their physical properties from those of the unmodified polymer have been related to the variation in chemical structure. These co-polymers, which are about 95% methylmethacrylate, have different co-monomers which introduce crosslinks and hydrogen bonds into the polymer. The modifications have changed the craze resistance relative to the homopolymer, with in some cases improvements of over 50%. This change in craze resistance is not uniform with change in crazing agent, so showing that the responses of the materials with the change in solubility parameter of the agents are not the same. Likewise the water absorption behaviour shows wide variation, the solubility ranging up to twice that of the homopolymer. Measurements of the fracture properties show that three of the polymers are significantly less ductile than the homopolymer, though this is masked by an increase of the elastic modulus in two.     

In vitro adhesion and biocompatability of osteoblast-like cells to poly(methylmethacrylate) and poly(ethylmethacrylate) bone cements

A bone cement, poly(ethylmethacrylate)/n-butylmethacrylate (PEMA/nBMA) has been developed with lower exotherm and monomer leaching compared to the traditional poly(methylmethacrylate)/methylmethacrylate (PMMA/MMA) cement. This study compares the in vitro biological response to the cements using primary human osteoblast-like cells (HOB). Cell attachment was qualified by immunolocalization of vinculin and actin cytoskeleton, showing more organization on PEMA/nBMA compared to PMMA/MMA. Proliferation was assessed using tritiated thymidine incorporation, and phenotype expression determined by measuring alkaline phosphatase (ALP) activity. An increase in proliferation and ALP activity was observed on PEMA/nBMA compared to PMMA/MMA. The results confirm the biocompatability of PEMA/nBMA, and an enhanced cell attachment and expression of differentiated cell phenotype.     

Compatibility studies of natural rubber/poly(methyl methacrylate) blends by viscometry and phase separation techniques

The compatibility of binary blends of natural rubber (NR) and poly(methyl methacrylate) (PMMA) has been analysed from the viscosity behaviour. For this, the equations developed by both Krighbaum and Wall, and their modified forms by Williamson and Wright, were used. The interaction between polymers in solution has been interpreted qualitatively based on the heat of mixing (ΔH) and interaction parameter (X1). Viscometry and spectroscopy studies and calculation of the heat of mixing and the interaction parameter indicated the heterogeneous nature of NR/PMMA blends. The effects of graft copolymer of natural rubber and poly(methyl methacrylate) (NR-g-PMMA) as an emulsifying agent on the interfacial properties of NR/PMMA blends were studied based on the phase separation behaviour. The demixing behaviour is found to be a function of graft copolymer concentration, mode of mixing, nature of solvent and molecular weight of homopolymers and graft copolymers. The demixing behaviour has been studied by noting the phase separation time and volume of the phase separated region. The addition of graft copolymer decreases the demixing behaviour of the blends. This revised version was published online in November 2006 with corrections to the Cover Date.     

Self-aligned and bundled electrospun fibers prepared from blends of polystyrene (PS) and poly(methyl methacrylate) (PMMA) with a hairy-rod polyphenylene copolymer

Bundled and self-aligned fibers were obtained by electrospinning blends of polystyrene (PS) and poly(methyl methacrylate) (PMMA) with a hairy-rod polyphenylene-g-polystyrene/poly(a-caprolactone) (PP-g-PS/PCL) copolymer. The self-alignment and bundling characteristics of these electrospun fibers were ascribed to the unique molecular architecture of the conjugated polymer, PP-g-PS/PCL, and its interactions with the solvent and the polymer matrixes used for the electrospinning. The self-alignment and bundling was found to be much more pronounced for PP-g-PS/PCL-PS blend when compared to PP-g-PS/PCL-PMMA blend. Furthermore we found that the degree of self-alignment of the fiber bundles was enhanced by increasing the amount of PP-g-PS/PCL in the blends but the alignment completely disappeared when the solvent dimethylformamide was changed to chloroform.     

The strain-rate,temperature and pressure dependence of yield of isotropic poly(methylmethacrylate) and poly(ethylene terephthalate)

The yield behaviour of poly(methylmethacrylate) (PMMA) has been investigated in tension and compression over a range of testing temperatures and strain-rates. Both tensile and compressive yield stresses were found to increase monotonically with increasing strainrate and decreasing temperatures. Compressive yield stresses were in general found to be more dependent on strain-rate.The results of this investigation have been correlated with previous published data for the dependence of the torsional yield stress of PMMA on hydrostatic pressure. This was done by a modification of a theory proposed by Robertson which uses the internal viscosity approach to yield in glassy polymers. The modified theory clearly explains the temperature and strain-rate dependence of the yield stress and provides a quantitative explanation of the differences in behaviour between tension and compression in terms of the dependence of yield on the hydrostatic component of the applied stress.The tensile yield behaviour of isotropic amorphous poly(ethylene terephthalate) (PET) sheets has also been investigated over a wide range of temperatures and strain-rates. No torsion or compressive yield stresses are available because of the sheet form of the PET, but the results obtained in tension are shown to be fully consistent with the above theory, and with other published work.Paper presented at Cambridge, April 1970, during conference on Yield, Deformation and Fracture of Polymers.     

Study of optical properties of potassium permanganate ($$\hbox {KMnO}_{4}$$) doped poly(methylmethacrylate) (PMMA) composite films

We have developed films of pure polymethylmethacrylate (PMMA) (0.5, 1, 2 and 5%) and potassium permanganate \((\hbox {KMnO}_{4})\)-doped PMMA composite films of thickness (\(\sim 100\, \upmu \hbox {m}\)) using the solution-cast technique. To identify the possible change that happen to the PMMA films due to doping, the optical properties were investigated for different concentrations of \(\hbox {KMnO}_{4}\) by recording the absorbance (A) and transmittance (\(T\%\)) spectra of these films using UV–Vis spectrophotometer in the wavelength range of 300–1100 nm. From the data obtained from the optical parameters viz. absorption coefficient (\(\alpha \)), extinction coefficient (\(\kappa \)), finesse coefficient (F), refractive index (\(\eta \)), real and imaginary parts of dielectric constant (\(\varepsilon _{\mathrm{r}}\) and \(\varepsilon _{\mathrm{i}})\) and optical conductivity (\(\sigma \)) were calculated for the prepared films. The indirect optical band gap for the pure and the doped-PMMA films were also estimated.     

Tensile properties and impact behaviour of poly(D(−)3-hydroxybutyrate)/rubber blends

A random ethylene-propylene rubber copolymer with functional ester or anhydride groups and an ethylene vinilacetate copolymer modified by a partial transformation of acetate groups in alcoholic groups were used as minor components to obtain binary poly(D(-)3-hydroxy-butyrate) blends by melt-mixing. The influence of the rubbery impact modifier on the morphology and on the tensile and high-speed fracture behaviour of such blends was investigated. Better properties were found when anhydride groups were present on the rubbery component. This was attributed to chemical interactions occurring between the dispersed phase and the matrix during the blending process.     

Mechanical properties of blends of poly(methyl methacrylate) and poly(vinylidene fluoride)

The mechanical properties of blends of the crystallizable polymer poly(vinylidene fluoride) and the amorphous material poly(methyl methacrylate) have been investigated as a function of composition both for glassy amorphous materials and for partially crystalline materials. The data obtained were interpreted in terms of the molecular and super-molecular structure of the blends and in terms of their dynamic properties.The main conclusions were that the mechanical properties are not strongly dependent on details of the distribution of the two components in the material nor on the crystal modifications present. The mechanical properties were found to depend primarily on the location of the glass transition temperature relative to the elongation temperature and on the presence or absence of crystalline regions. The degree of crystallinity was found to play an important role in determining the properties only at lower values of this quantity. The advantage of these blends is that the important parameters, namely, the degree of crystallinity and the location of the glass transition temperature, can be adjusted at will by varying the composition appropriately. This allows well-defined variations of the mechanical properties to be achieved.     

Time and temperature dependence of the scratch properties of poly(methylmethacrylate) surfaces

Most existing models describing the scratch properties of materials take into account forces acting at the interface between the material and a grooving tip, but do not consider the stress and strain properties of the material far beneath or ahead of the tip. In the case of polymer scratches, there are no models at all which take into account the viscoelastic viscoplastic behaviour of the material. In standard indentation tests with a non moving tip, the elastic plastic boundary and the limits of the region subjected to hydrostatic pressure beneath the tip are known. These models were used to analyse the geometry of the grooves left on the surface of a viscoelastic viscoplastic body by a moving cone-shaped diamond tip having a radius of about 40 m. A new apparatus was built to control the velocity of the tip over the range 1 to 10⁴ m/s, at several different temperatures from –10°C to 100°C. The material was a commercial grade of cast poly(methylmethacrylate) (PMMA). The normal and tangential loads and groove size were used to evaluate the dynamic hardness, which behaved like a stress and temperature activated process. Values of the activation energy and volume of the dynamic hardness and of the interfacial shear stress were in good agreement with those usually attributed to the mechanical properties of PMMA.