Ferenc Cser

Sol–gel derived composites from poly(silicic acid) and 2-hydroxyethylmethacrylate: thermal, physical and morphological properties

Abstract Hybrid materials based on poly(silicic acid) and 2-hydroxyethylmethacrylate were prepared and characterized. The glass transition temperatures of a homologous series of samples were measured by dynamic mechanical thermal analysis and the location of the transition and shape of the spectra shown to be dependent on the morphology of the inorganic phase which was able to be manipulated by variation of synthetic conditions. A number of other techniques including small angle X-ray scattering, electron microscopy, density and free volume measurements were used to help elucidate inorganic–organic miscibility and structure. It was shown that incorporation of organic polymeric phase to crosslinked inorganic silicate led to the formation of the system that is similar to interpenetrating polymeric networks. A high level of miscibility as determined by small angle X-ray scattering and transmission electron microscopy was demonstrated. This was also demonstrated in DMTA traces as seen by the mobility of the organic phase being determined by the degree of crosslinking of the inorganic component. Nonetheless, there appear to be a slight influence of silicate architecture on molecular packing and miscibility. Highly branched, higher molecular weight silicate materials appear to be slightly less miscible.

Morphology-property relationships in ABS/PET blends. I. Compositional effects

Novel blends of PET and ABS were prepared by extrusion and injection molding. DSC and DMTA studies show that PET and ABS are immiscible and that the blends consist of four phases : SAN, grafted polybutadiene, amorphous PET, and minor amounts of crystalline PET. The morphology was investigated by transmission electron microscopy on OsO 4 -stained and unstained sections and by scanning electron microscopy of alkali- and solvent-etched surfaces. These techniques reveal that the two major domains, SAN and amorphous PET, interpenetrate and are cocontinuous over the compositional range of 30-70 wt % PET. The yield stress and flexural modulus increase in an almost linear fashion as the weight fraction of PET in the blend is increased. In contrast, the notched Izod impact energy passes through a maximum and the Dart impact energy shows a step transition at 50 wt % PET. SEM studies of the Izod fracture surfaces exhibit considerable plastic deformation in both domains when the specimens are tough, indicating that both phases participate in the toughening process.

Thermal properties of polypropylene post-consumer waste (PP PCW)

Differential scanning calorimetry has been used to study the heat flow during melting and crystallisation of a range of polypropylene post-consumer waste (PP PCW) grades and blends. The heat flow curves and the heat capacity curves indicated that the PP PCW grades and blends contained contaminants even after manual sorting and a cleaning process. The enthalpies of the PP PCW grades were lower than that for the virgin grades, as a result of degradation. Small amounts of polymeric contaminants (up to 10%) did not affect the enthalpies of PP PCW although other contaminants may have had some effect. The enthalpies of the PCW blends could in general be predicted by a linear additive rule, which is of importance for recycling a variety of PP PCW products.

Morphology–property relationships in ABS/PET blends. II. Influence of processing conditions on structure and properties

The effect of processing temperature on the low-speed tensile and high-speed impact properties of novel ABS/PET blends was investigated. In agreement with the conclusions from related studies of ABS/PC blends, it appears that catalytic impurities in the ABS accentuate the propensity of PET for chain scission. Due to the cocontinuous structure of the blend, the hydrolytic or thermomechanical degradation of the PET results in a dramatic loss in mechanical properties which can be explained by the entanglement theory for fracture and the Orowan brittle–ductile hypothesis.

Reversible Melting of Thermally Fractionated Polyethylene

Different grades of linear low density polyethylenes (LLDPEs) have been quenched cooled step-wise and crystallised isothermally at (a series of increasing) temperatures in a DSC (thermal fractionated samples). These samples have been investigated by temperature modulated DSC (MDSC). The heat flow curves of the thermal fractionated materials were compared with those obtained from samples crystallised at a relatively slow cooling rate of 2 K min-1(standard samples).The melting enthalpy obtained from the total heat flow of the thermal fractionated samples was 0-10 J g-1higher than those of standard samples. The melting enthalpy obtained from the reversing heat flows was 13-31 J g-1lower in the thermal fractionated samples than in the standard samples. The ratio of the reversing melting enthalpy to the total melting enthalpy increased with decreasing density of the PE. The melting temperature of the endotherms formed by the step-wise cooling was 9 K higher than the crystallisation temperature.

Miscibility Studies on cross-linked EVA/LLDPE Blends by TMDSC

Cross-linked polymers have particular rheological responses during reprocessing, e. g. if the material is recycled, special processing conditions are required. Other virgin polymers can be used as a blending component to enhance rheological properties.Bi-layer film of EVA/LLDPE was produced on a blown film line and cross-linked by high-energy radiation. This film was ‘agglomerated’ then reprocessed in a twin-screw extruder with virgin LLDPE and blown into film. The miscibility of the blend components was then studied using a TA Instruments temperature modulated differential scanning calorimeter (TMDSC).It was found that the cross-linked EVA/LLDPE scrap and the LLDPE have a slight miscibility in the liquid state. A bigger portion of LLDPE was miscible (dissolved) in EVA in low LLDPE blends. A positive deviation in the heat capacity of the LLDPE component compared to the additivity rule indicated melting to be more reversible in the first heating cycle. This initial miscibility was attributed to being induced by high shear during processing. A smaller positive deviation also occurred in the second heating cycle. This was attributed to intrinsic miscibility.

Crystallinity of polypropylene-silica ash composites affected by the mixing conditions - DSC studies

For particulate polymeric composites, mixing is a crucial step to be optimised; and in the process-control stage, identification of the factors that influence mixing is important for a deeper understanding of the composite mechanical performance. A mixing study of a hydrophobic polymer matrix (polypropylene) filled with a hydrophilic particulate-filler (silica from rice husk ash) was carried out using a batch mixer at a constant filler fraction of 20% (w/w). The study involved varying the mixing-time, screw speed and mixing-chamber temperature used to prepare the composites. Mechanical analysis of the samples showed that the tensile strength and modulus values were dependent on the mixing conditions. Furthermore, DSC studies of the samples revealed that the degree of crystallinity was also affected by the mixing conditions. The observed increase in the tensile strength was attributed to the increased filler-matrix interactions; however, there was difficulty in analysing how the mixing conditions influenced the tensile strength because of a lack of extensive data on filler dispersion. The increase in crystallinity, as affected by mixing conditions, was thought to improve the filler-matrix interaction leading to an increased tensile modulus. Interestingly, samples showed permanent morphological changes after their previous thermal histories were erased, suggesting that there was significant interaction between the silica ash particles and the polymer matrix, even though they are quite incompatible. A statistical analysis based on the tensile data was carried out to optimise the state of mixing. The results indicate that (i) the optimised state of mixing correlated with higher crystallinity and (ii) changes in the parameters of physical mixing might significantly affect the homogeneity and crystallinity, both of which are related to the mechanical performance of the composites. Furthermore, reducing the particle size of the silica ash was also found to increase the crystallinity, which was in turn related to the improved tensile properties of the composites. The investigation attempts to highlight that for apparent incompatible system, homogeneity is very important but it alone cannot explain the moderate filler-matrix interactions and filler bonding characteristics that are known to contribute to improved tensile properties. Somehow, composites mechanical properties are improved by optimising the physical mix-state, and by modifying the particle size but it seems like that the net effect is due to increased interactions. In any case, it is clear that optimisation of interactions can be achieved by obtaining a homogeneous phase.

Reversed Annealing of Thermal Fractionated Polyethylenes by TMDSC

Polyethylene samples prepared by thermal fractionation (TF) were annealed in several consecutive cycles in a temperature modulated DSC (TMDSC) at a temperatures one °C below the peak temperatures, increased from cycle to cycle relative to these peaks. The transition enthalpy of each cooling cycle was greater or equal to that of the preceding heating cycle. The total heat-flows of each heating cycle corresponded to those of the samples in the reference state up until the vicinity of the annealing temperature. During the annealing, the heat capacities decreased to a lower value over a one minute period. The thermal memory effect caused by the thermal fractionation was eliminated by a small overheating of the material for a short time. The fast disappearance of the thermal memory by a relatively very small degree of heating above their melting temperature denies a long range physical separation of macromolecules by TF.

Annealing of Polypropylene/Polyethylene Blends Near to the Melting Points in TMDSC

Annealing experiments have been carried out just below the melting temperature of both polyethylene (LLDPE) and polypropylene (PP) and their blends. The total melting enthalpy measured after the annealing cycle was greater by 10-15% with respect to the value having been measured before it. During the annealing period the heat capacity decreases to a lower value within the first 2-3 min. Heat capacities of PP (either in pure form or in the blends) measured during the heating cycle following the annealing cycle have the same value as during the cooling section. The heat capacities of the LLDPE in the heating cycle following the annealing were those of the preceding heating cycle. The total heat flows in the cooling section following the annealing cycle were greater than those in another cooling cycle at the same temperatures indicating that the crystallisation takes place during the cooling rather than during the annealing periods.The presence of LLDPE decreases the crystallisation temperature of PP. The presence of SEBS in the blend results in a greater crystallisation temperature than that of pure PP. The crystallisation temperature of LLDPE increases with increasing levels of PP.