Gabriël Groeninckx

Immiscible polymer blends of semicrystalline biocompatible components: thermal properties and phase morphology analysis of PLLA/PCL blends

Abstract Immiscible binary blends of poly( l , l -lactide) (PLLA), and poly(e-caprolactone) (PCL), with 90/10, 80/20 and 70/30xa0wt% compositions, as well as ternary PLLA/PCL blends containing 0.5–5xa0wt% of a triblock PLLA/PCL/PLLA copolymer, were obtained by melt mixing using a twin screw extruder. Optical microscopy investigation of binary blends revealed the immiscibility of the components. The thermal behaviour of the blends was investigated by DSC and DMTA and compared with that of pure PLLA. The PLLA crystallization rate was enhanced in the presence of PCL domains. Morphological analysis of the cryofractured and etched–smoothed surfaces was carried out by SEM on both binary and ternary blends. A dimensional analysis of the PCL domains in binary and ternary blends was also performed in order to evaluate the influence of the presence of the triblock copolymer on the dispersion mode of PCL in the PLLA matrix.

Rheological behaviour of thermoplastic elastomers from polypropylene/acrylonitrile-butadiene rubber blends: effect of blend ratio, reactive compatibilization and dynamic vulcanization

Abstract The rheological behaviour of polypropylene (PP)/acrylonitrile–butadiene rubber (NBR) blends has been investigated with special reference to the effect of blend ratio, compatibilization and dynamic vulcanization. The morphology of the extrudates and the size and distribution of domains were examined. PP/NBR blends show pseudoplastic behaviour, which is evidenced by the decrease in viscosity with increasing shear rate. The melt viscosity of these blends increased with increasing nitrile rubber concentration and shows negative deviation from the theoretically predicted values. Compatibilization of the blends with phenolic-modified polypropylene (Ph-PP) increases the melt viscosity at low concentrations of Ph-PP. The rheological behaviour of PP/BR blends was correlated with the blend morphology. Dynamic vulcanization has a decreasing effect on die swell values. The effect of temperature on the melt viscosity of the blends was examined and attempts have been made to construct a shear rate–temperature superposition master curve. The melt-flow index values for these blends were measured and have been correlated with rheometer data to develop a master curve for different blend compositions. The morphological analysis indicates that compatibilization of the blends prevents the coalescence of dispersed NBR domains during annealing.

Reactive compatibilisation of heterogeneous ethylene propylene rubber (EPM)/nylon 6 blends by the addition of compatibiliser precursor EPM-g-MA

Abstract Blends of ethylene–propylene rubber (EPM) and nylon 6 are immiscible and highly incompatible. These blends are characterised by a two-phase morphology, narrow interface, and poor physical and chemical interactions across the phase boundaries. Therefore a reactive route was employed to compatibilise these blends by the addition of maleic anhydride grafted EPM (EPM-g-MA). In this reactive route, the maleic anhydride group of EPM reacts with the amino end group of nylon forming a graft copolymer of nylon and EPM (nylon-g-EPM) at the blend interface which decreases the interfacial tension and reduces the coalescence. The influence of the concentration of EPM-g-MA, blend composition, molecular weight of nylon 6, mode of addition of EPM-g-MA and mixing time on the phase morphology of the blends was studied quantitatively by scanning electron microscopy and image analysis. It was found that the addition of EPM-g-MA reduces the domain size of the dispersed phase followed by a levelling off at high concentrations; the levelling off is an indication of interfacial saturation. The optimum amount of the compatibiliser required to saturate unit volume of the interfacial zone was estimated from the emulsification curves. This optimum concentration of the compatibiliser can be considered as the so-called critical micelle concentration (CMC) above which micelles of the copolymer are formed in the bulk phase, which is highly undesirable. Emulsification master curves were obtained by plotting the reduced domain size as a function of EPM-g-MA for the different blend compositions. This was explained based on the interfacial area occupied by the compatibiliser molecule at the blend interface. The experimental results were compared with the current compatibilisation theories. The phase morphology development was studied as a function of the mixing time in the presence and absence of compatibiliser. The influence of reactive compatibilisation on phase inversion and the co-continuous nature of the blends was also investigated. Finally the stability of the blend morphology was analysed by high temperature isothermal annealing in the presence and absence of compatibiliser

Miscibility and morphology of binary polymer blends of polycaprolactone with solution-chlorinated polyethylenes

Abstract Binary blends of solution-chlorinated polyethylenes (CPE) with polycaprolactone (PCL) were prepared by the coprecipitation technique. The phase behaviour of the mixtures was determined using optical microscopy, light transmission measurements, dynamic mechanical analysis and differential scanning calorimetry. The superstructure of the semicrystalline CPE/PCL blends was studied by small-angle X-ray diffraction, while the melting behaviour of PCL in the blends was investigated by differential scanning calorimetry. The miscibility was found to be dependent on the chlorine content of CPE and the temperature, while CPE is segregated interfibrillarly or interspherulitically during the crystallization of PCL in the blend. The double melting behaviour is attributed to a secondary crystallization process.

Fractionation and thermal behaviour of linear low density polyethylene

Abstract An ethylene 1- octene copolymer has been fractionated by molecular weight using successive solution fractionation (s.f.f.). The fractions obtained and the original copolymer were analysed with respect to the short chain branching distribution using analytical temperature rising elution fractionation (a.t.r.e.f.). A bimodal, very wide branching distribution is observed, both for the non-fractionated polymer and for the s.s.f. fractions. A decrease of the average degree of branching with increasing average molecular weight of the fractions is observed. The melting behaviour of isothermally crystallized samples was studied using differential scanning calorimetry (d.s.c.). The low-temperature melting endotherm is caused by the melting of small crystals, composed of very strongly branched molecules. The endotherms above the isothermal crystallization temperature are caused by the melting of thicker crystals, composed of weakly branched molecules.

Ultimate mechanical properties of rubber toughened semicrystalline PET at room temperature

Abstract A comparative fundamental study was performed regarding the notched impact toughening performance of various rubber modified semicrystalline polyethylene terephthalate (PET) systems. Various modifiers with and without functional groups were evaluated: ethylene- co -propylene rubber (EPR), maleic anhydride grafted EPR (EPR- g -MA), glycidyl methacrylate grafted EPR (EPR- g -GMA x ) and ethylene–glycidyl methacrylate copolymers (E–GMA x ). Both binary and ternary blends (consisting of a preblend of EPR and a functionalised modifier) were examined. The most effective toughening route for PET is provided by dispersing a preblend of EPR and a low amount of E–GMA x . A minimum dispersed phase concentration of 30xa0wt% is needed to obtain a pronounced improvement of the impact strength and to induce a brittle–ductile transition of the fracture mode. The impact behaviour of the rubber toughened PET is primarily controlled by the morphological characteristics, i.e. the interparticle distance. An equal critical interparticle distance (IDc) of 0.1xa0μm was established experimentally for the different GMA compatibilised systems. This IDc is found to be independent of the amount of GMA functionalities present, the way of incorporation in the chain (grafting or copolymerisation) and the nature of the compatibiliser. The ternary PET/(EPR/E–GMA8) blends provided the best ultimate mechanical properties, displaying highly (15-fold) increased impact strengths and reasonable elongations at break.

Styrene–butadiene rubber/natural rubber blends: Morphology, transport behavior, and dynamic mechanical and mechanical properties

Blends of styrene–butadiene rubber (SBR) and natural rubber (NR) were prepared and their morphology, transport behavior, and dynamic mechanical and mechanical properties were studied. The transport behavior of SBR/NR blends was examined in an atmosphere of n-alkanes in the temperature range of 25–60°C. Transport parameters such as diffusivity, sorptivity, and permeability were estimated. Network characterization was done using phantom and affine models. The effect of the blend ratio on the dynamic mechanical properties of SBR/NR blends was investigated at different temperatures. The storage modulus of the blend decreased with increase of the temperature. Attempts were made to correlate the properties with the morphology of the blend. To understand the stability of the membranes, mechanical testing was carried out for unswollen, swollen, and deswollen samples.

Miscibility, crystallization and melting behaviour, and semicrystalline morphology of binary blends of polycaprolactone with poly(hydroxy ether of bisphenol A)

Abstract Blends of poly(hydroxy ether of bisphenol A) (Phenoxy) with polycaprolactone (PCL) were prepared by the coprecipitation technique. The melt miscibility of the polymers was studied by optical microscopy, light transmission measurements and dynamic mechanical analysis. The crystallization kinetics of PCL in the miscible Phenoxy/PCL blends were studied using optical microscopy and the segregation behaviour of Phenoxy due to the crystallization of PCL was examined by means of optical microscopy and small-angle X-ray diffraction, while the melting behaviour of PCL in the blend was explored by differential scanning calorimetry. The polymers were found to be miscible over the entire composition and temperature range (up to 200°C), while Phenoxy is segregated interlamellarly as well as interfibrillarly and interspherulitically during the crystallization process of PCL.

Reactive compatibilisation of A/(B/C) polymer blends - Part 2. Analysis of the phase inversion region and the co-continuous phase morphology

Abstract The blend polyamide 6 (PA-6)/poly(methyl methacrylate) (PMMA) can be compatibilised by means of the reactive copolymer styrene-maleic anhydride with 20 wt% maleic anhydride (SMA20). The region of phase co-continuity has been analysed for the non-compatibilised and the compatibilised blends with scanning electron microscopy (SEM). The blend composition range of phase co-continuity was shifted to a lower PA-6 content when compatibiliser (SMA20) was added and the co-continuous structures were observed over a much narrower composition range. The effect of the molecular weight of PA-6 on the composition range of phase co-continuity was also analysed; it was found to be shifted to lower PA-6 content with decreasing molecular weight of PA-6. This shift could be interpreted by measuring the melt-viscosity of the different polymers using capillary rheometry. The analysis of the dynamic mechanical properties of the blends confirmed the results obtained with SEM; a clear change in storage modulus (log E′ ) and damping (tan δ) was observed in the phase inversion region. Finally, the crystallisation behaviour of PA-6 in the blends was investigated during cooling from the melt with differential scanning calorimetry. Fractionated crystallisation was observed in the blends where PA-6 forms the dispersed phase.

Morphology and melting behaviour of semi-crystalline poly(ethylene terephthalate): 3. Quantification of crystal perfection and crystallinity

Abstract The semi-crystalline state of bulk-crystallized poly(ethylene terephthalate) and its relation to the melting behaviour of the polymer have been thoroughly investigated as a function of the thermal history by wide-angle X-ray diffraction. The experimental data, analysed according to the method of Ruland, allow estimation of the absolute degree of crystallinity and the diffuse disorder scattering. The results of this study give a better and more complete insight into the complex thermal behaviour of PET; moreover they corroborate the need for a broad experimental approach in studies related to the melting behaviour of polymers.