Morphology development and phase inversion during dynamic vulcanisation of EPDM/PP blends

Morphology development and phase inversion were investigated during dynamic vulcanisation of ethylene–propylene–diene terpolymer (EPDM)/polypropylene (PP) blends. The effects of viscosity ratio and cross-linking reactions were also addressed. EPDM/PP blends were dynamically vulcanised in a Haake batch mixer using resole and SnCl₂ as cross-linking agents. The morphology development and cross-linking degree with reaction time were followed by morphology analysis (SEM and TEM) and measurement of EPDM gel content, respectively. For the same reaction time, it was found that the EPDM gel content decreased when the low-molecular-weight EPDM was used. As a result, the morphological development was delayed and the phase-inversion point was shifted to higher reaction times, allowing us to monitor morphological development during a thermoplastic vulcanisate (TPV) preparation. Using the low-molecular-weight EPDM and increasing the PP viscosity accelerated the morphological development, shifting phase-inversion to lower reaction times. While blend composition influenced final TPV morphology, it had a minor effect on the mechanism of morphological development. A correlation between cross-linking degree and morphology development was established. The results obtained allowed to propose a mechanism of morphology development during dynamic vulcanisation of the EPDM/PP blends, including phase inversion.     

Morphology,rheological and crystallization behavior in thermoplastic polyurethane toughed poly(l-lactide) with stereocomplex crystallites

Melt-blending poly(l-lactide) (PLLA) with elastomers has been well demonstrated to improve toughness of PLLA. Here, we show a poly(d-lactide) (PDLA) grafted thermoplastic polyurethane (TPU) (TPU-g-PDLA) toughed PLLA with simultaneous formation of few amount stereocomplex crystallites (SCs) which exhibited higher efficient toughening than that of PLLA with TPU. The TPU-g-PDLA was prepared by the in-situ melt-reaction of TPU and PDLA with 4, 4’-diphenylmethane diisocyanate (MDI). A comparative study on morphology, rheological and crystallization behavior was also carried in PLLA/TPU, PLLA/TPU-g-PDLA and PLLA/TPU/PDLA samples. The PLLA/TPU-g-PDLA samples show the highest crystallization rate, complex viscosity, impact strength and tensile strength among PLLA/TPU, PLLA/TPU-g-PDLA and PLLA/TPU/PDLA samples, indicating that the higher interfacial interaction between TPU-g-PDLA and PLLA. Furthermore, TPU chains in TPU-g-PDLA were thought to break the intermolecular interaction of PLLA and rapid its crystallization and increase crystallinity.     

A polymer network based on thermoplastic polyurethane and ethylene-propylene-diene elastomer via melt blending: morphology, mechanical properties, and rheology

Blends of thermoplastic polyurethane (TPU) and ethylene-propylene-diene elastomer (EPDM) were prepared via a melt blending, and morphology, mechanical properties, and rheology were studied. Scanning electron microscopy (SEM) micrographs demonstrated that a network of EPDM domain was formed in TPU matrix, and became finer and more perfect with addition of 8 wt% EPDM into TPU. Dynamic mechanical analysis (DMA) and Fourier transformed infrared spectroscopy (FTIR) investigation indicated that EPDM was thermodynamically miscible with the soft segments of TPU and incompatible with the hard segments. The formation of the network was resulted from the competition of compatible and incompatible segments of TPU with EPDM. The tensile strength and elongation at break achieved a significant improvement with addition of EPDM, and obtained the optimum values of 39.21 MPa and 2659%, respectively, when EPDM content was 8 wt%. PEO-g-MA as a compatibilizer was employed to improve the compatibilization between EPDM and the hard segments of EPDM, and consequently, the network became finer and more perfect. The evaluation of rheological properties revealed that the introduction of EPDM into TPU resulted in a reduction of the viscosity at high shear rate and a decrease of the flow activation energy; thus the processability of the blends was improved.     

Preparation and flammability of EPDM/PP/Mg(OH)2 dynamic vulcanizates

Magnesium hydroxide (MH) flame retardant dynamic vulcanized ethylene‐propylene‐diene terpolymer (EPDM)/polypropylene (PP) thermoplastic vulcanizates (TPVs) were prepared by a twin‐screw extruder. Influences of MH on their morphology, mechanical properties, flammability, and crystallization behavior have been investigated. Static tensile measurements exhibited that TPVs have higher mechanical properties than un‐vulcanized EPDM/PP/MH blends (UVBs). Scanning electron microscopy (SEM) studies showed that the formation of the larger‐size “micro‐encapsulated structure” where the MH aggregates were covered with a cross‐linked rubber phase improved the interaction between MH and polymer matrix. Results of limiting oxygen index (LOI) and microscale combustion calorimetry (MCC) confirmed that TPVs had superior fire‐resistant properties to UVBs. SEM images showed that more uniform and compact charred layers were generated in TPVs. The differential scanning calorimetry (DSC) results indicated that the crystallization behavior of the flame retardant TPVs changed marginally with increase in MH content. Copyright © 2009 John Wiley & Sons, Ltd.     

Sub-micrometer thermoplastic vulcanizates obtained by reaction-induced phase separation of miscible mixtures of poly(ethylene) and alkyl methacrylates

Sub-micrometer (μm) thermoplastic vulcanizates (TPVs) with cross-linked rubber particles with sizes ranging from 70 to 400 nm were prepared by reaction-induced phase separation (RIPS) of initially miscible blends of poly(ethylene) (PE), lauryl methacrylate (LMA) and divinylbenzene (DVB). Cross-linking under static conditions led to (partial) connectivity of the rubber particles via chemical bridging of grafted PE chains. Dynamic preparation conditions caused the connected structure to break-up, which led to a significant enhancement of the mechanical properties and the melt processability. The addition of 25-80 wt% extender oil resulted in a reduced complex viscosity and yield stress in the melt, without deteriorating the mechanical properties. The relatively good elastic recovery and excellent ultimate properties of these high hardness TPVs may be explained by the sub-μm rubber dispersions.     

Structure and properties of dynamically cured EPDM and ionomer blends

The structure and properties of dynamically cured ethylene-propylene-diene terpolymer (EPDM) and ionomer blends have been studied. The blends were prepared in a laboratory internal mixer, where EPDM was cured under shear in the presence of ionomer with dicumyl peroxide (DCP) under different shear conditions. The effects of EPDM/ionomer compositions, DCP concentration and the intensity of shear mixing were investigated using capillary rheometer, differential scanning calorimeter (DSC) and scanning electron microscopy (SEM) techniques. Two kinds of poly(ethylene-co-methacrylic acid) ionomers containing different metal ions(Na⁺ and Zn⁺⁺) were compared and the effect of the metal ion type for neutralization was considered. The Zn-neutralized ionomer showed better miscibility with EPDM than the Na-neutralized ionomer. It is concluded from the rheological properties, crystallization behavior and morphology that the dynamically cured EPDM and Zn-ion ionomer blends show the behavior of a thermoplastic interpenetrating polymer network (IPN).     

Use of wollastonite in a thermoplastic elastomer composition

Thermoplastic elastomer compositions (TPEs) based on wollastonite-filled SEBS/PP/oil blends were prepared and characterized. The development of new TPEs with improved mechanical strength may broaden their applications, especially for soft goods. Wollastonite is a natural filler that combines high thermal stability with low health hazard in comparison to other fibrous inorganic fillers. Morphological, thermal and mechanical properties of the composite materials were studied by transmission electron microscopy (TEM), thermogravimetry (TGA), tensile tests and dynamic mechanical analysis (DMA). The results indicate that the filler was mainly distributed as nanoparticles in the PS domains, improving the mechanical resistance of the materials even at low concentration (2 phr).     

Morphology and non-isothermal crystallization of dynamically vulcanized PP/EPDM blends in situ compatibilized via magnesium dimethacrylate

Polypropylene/ethylene-propylene-diene rubber (PP/EPDM) blends in situ compatibilized by magnesium dimethacrylate (MDMA) were fabricated via peroxide-induced dynamic vulcanization. Scanning electron microscope observation indicated that the size of cross-linked EPDM particles decreased with incorporation of MDMA. Polarizing Optical Microscope (POM) analysis suggested that the spherulite size of PP phase decreased sharply with incorporation of MDMA during dynamic vulcanization. The Pseudo-Avrami, Ozawa and Mo's models were applied to analyze the non-isothermal crystallization kinetics of the composites. The analyzed data indicated that the crosslinked EPDM particles and homopolymerized MDMA acted as heterogeneous nucleating agents, which enhanced the crystallizability and decreased the spherulite size of the PP phase. In addition, the non-isothermal crystallization activation energy (ΔE) was calculated through the Kissinger and Friedman methods, and the ΔE value was found increase with incorporation of MDMA.     

The distribution coefficient of oil and curing agent in PP/EPDM TPV

The distribution coefficients of oil and curing agent in PP/EPDM TPV were calculated by measuring the melting point of the PP phase using differential scanning calorimetry (DSC). The PP/EPDM TPV was prepared by using a twin screw extruder and a peroxide curing agent was used. The peroxide induces the degradation of PP, resulting in the decrease of T_m. The oil in PP phase also decreases the Tm. Based on the T_m difference among pure PP and PP/EPDM TPV before and after extraction by cylcohexane, the calculated oil distribution coefficient is 0.537. The addition sequence of PP, oil, and curing agent has a significant effect on the T_m and the calculated curing agent distribution coefficient is 0.52. Both of the coefficients are less than 1. Based on the calculation of the two coefficients, a rationale design of thermoplastic vulcanizate (TPV) can be made by proper control of raw materials, addition sequence, and processing parameters. Copyright © 2007 John Wiley & Sons, Ltd.     

Preparation of polypropylene (PP)/ethylene octene copolymer (EOC) thermoplastic vulcanizates (TPVs) by high energy electron reactive processing

Thermoplastic vulcanizates (TPVs) based on 50/50 composition of PP/EOC blend were prepared by electron induced reactive processing. To facilitate dynamic crosslinking in the PP/EOC blend, a 1.5 MeV electron accelerator was directly coupled to an internal mixer to induce chemical reactions via high energy electrons under dynamic conditions of melt mixing process. This kind of setup has been conceptualized for the first time in our laboratory and termed as electron induced reactive processing (EIReP) technique. Mechanical, morphological, and rheological properties of PP/EOC TPVs were studied with special reference to the exposure time (16–64 s) keeping absorbed dose (100 kGy) and electron energy (1.5 MeV) invariable. Chain scission dominates over chain crosslinking in both EOC as well as PP phases with the increase in exposure time. The primary factor is found to be the predominance of oxidative degradation during electron induced reactive processing in air atmosphere. The above observation was supported by Fourier Transform Infrared analyses and gel content values. Furthermore, it was found that mechanical properties depend not only on the extent of degradation in the blend system but also on the state and the mode of dispersion of the blend components.     

Mechanical properties of thermoplastic polyester elastomer controlled by blending with poly(butylene terephthalate)

Thermoplastic polyester elastomer (TPEE) blends with poly(butylene terephthalate) (PBT) were prepared by melt compounding for the phase morphology and mechanical property studies. Although PBT is immiscible with the continuous soft poly(tetramethylene glycol) (PTMEG) phase of TPEE, it is miscible with the discrete hard PBT one of TPEE. Therefore, PBT and TPEE are compatible and their blends reveal very low level of interfacial tension and very small size of discrete domains, as well as good interfacial adhesion between two phases, which provide high possibility to prepare TPEE alloys with controllable properties. Mechanical test results reveal that both the modulus and yield and tensile strengths increase with increasing weight ratios of PBT. The increased system rigidity and decreased system plasticity are further confirmed by the cyclic tensile tests. The main objective of this work is to provide useful information on the structure and property control of TPEE by simple mixing with aromatic polyesters.     

Mechanical properties and enzymic degradation of thermoplastic and granular sago starch filled poly(ε-caprolactone)

The mechanical, morphological and biodegradation properties of two types of poly(ε-caprolactone)/sago starch (PCL/sago) composites were investigated i.e. dried granulated sago starch and undried thermoplastic sago starch (TPSS). Thermoplastic starch was extruded with a twin screw extruder model Haake Rheomix (TW100 attached to a Haake Rheometer (Haake Rheodrive 5000). The composites were compounded with a Haake internal mixer (Haake Rheomix 3000) attached to the Haake Rheometer. Tensile properties were determined with the Monsanto Tensometer T10. A Shimadzu UV-160A visible UV spectrophotometer was used to monitor the liberation of carbohydrate as a consequence of starch hydrolysis by α-glucoamylase. Determining the weight loss of composites as well as the acid liberated from PCL also monitored biodegradation. The results indicate that dried granulated sago starch function better as fillers in terms of mechanical properties and the ease of biodegradation. However, TPSS imparted better yield strength to the composites. Poor wetting of starch accounts for the decreased mechanical properties at higher starch concentration as agglomeration occurs. While the rigid granular starch retained their shape in the composites, thermoplastic starch that is surrounded by microvoids is easily deformed due to plasticization.     

Morphology changes of polyvinylidene fluoride membrane under different phase separation mechanisms

In this study, the strong morphology changes of polyvinylidene fluoride (PVDF) membrane were demonstrated by changing phase separation process from a diffusion induced phase separation (DIPS) to its combination with a thermally induced phase separation (TIPS) which can be attained via changing the diluent – dibutyl phthalate (DBP) content in solvent – N,N-dimethylacetamide (DMAc). The solvent became poor when it mixed with DBP, so TIPS could occur in the quenching process which resulted in a rapid crystallization process. In this process, the porous skin and interlocked small crystallite particle (or bi-continuous) morphologies were formed, while the porous skin and leaf-like network morphology came from the rapidly crystallizing in TIPS, the large spherulite and dense skin could be attributed to the relaxed crystallization in DIPS, the finger-like macro-void and dense skin resulted from the liquid–liquid phase separation in DIPS. Simply speaking, the different membrane morphologies can be obtained by changing the DBP content in DMAc and the coagulation bath temperature.     

Aging of ethylene-propylene-diene monomer (EPDM) in artificial weathering environment

Ethylene-propylene-diene monomer (EPDM) containing ENB as diene was exposed to artificial weathering environment for different periods of time. The changes of appearance, morphology, mechanical properties and chemical structures were monitored by spectrophotometer, glossmeter, microscope, computer-controlled tensile testing, hardness measurements and Fourier Transform Infrared (FTIR) spectroscopy. Crosslink density of EPDM specimens was measured by the solvent swell method. The results showed that the surface of EPDM became redder, yellower and lighter in the first stage of aging and then remained almost unchanged. The specular gloss reached a maximum when the sample was exposed for 18 days and then decreased. The aging process proceeded predominantly via crosslinking. The tensile strength increased with increase in crosslink density up to an optimum value and thereafter decreased with further increase in crosslink density. FTIR spectra confirmed the formation of carbonyl groups in an artificial weathering environment.     

Influence of the fibre/matrix interface on ageing mechanisms of glass fibre reinforced thermoplastic composites (PA-6,6, PET, PBT) in a hygrothermal environment

A study of the properties of short glass fibre reinforced thermoplastic composites based on poly(ethylene terephthalate), poly(butylene terephthalate) and polyamide-6,6 in an aggressive environment is reported. The influence of the fibre/matrix interface on the composite behaviour in a moist environment is especially studied. Competitive phenomena may explain differences observed according to the nature of the fibre surface treatment. Among them these characteristics may be an intrinsic fragility of some chemical interfacial bonds, the hydrophilicity of some chemical groups, the presence of long macromolecular chains neighbouring the interface or of a transcrystalline interfacial area.     

Morphology development and crystallization behavior of poly(ethylene terephthalate)/poly(trimethylene terephthalate) blends

The spherulite morphology and crystallization behavior of poly(ethylene terephthalate) (PET)/poly(trimethylene terephthalate) (PTT) blends were investigated with optical microscopy (OM), small-angle light scattering (SALS), and small-angle X-ray scattering (SAXS). The thermal analysis showed that PET and PTT were miscible in the melt over the entire composition range. The rejected distance of non-crystallizable species, which was represented in terms of the parameter δ, played an important role in determining the morphological patterns of the blends at a specific crystallization temperature regime. The parameter δ could be controlled by variation of the composition, the crystallization temperature, and the level of transesterification. In the case of two-step crystallization, the crystallization of PTT commenced in the interspherulitic region between the grown PET crystals and proceeded until the interspherulitic space was filled with PTT crystals. The spherulitic surface of the PET crystals acted as nucleation sites where PTT preferentially crystallized, leading to the formation of non-spherulitic crystalline texture. The SALS results suggested that the growth pattern of the PET crystals was significantly changed by the presence of the PTT molecules. The lamellar morphology parameters were evaluated by a one-dimensional correlation function analysis. The blends that crystallized above the melting point of PTT showed a larger amorphous layer thickness than the pure PET, indicating that the non-crystallizable PTT component might be incorporated into the interlamellar region of the PET crystals. With an increased level of transesterification, the exclusion of non-crystallizable species from the lamellar stacks was favorable due to the lower crystal growth rates. As a result, the amorphous layer thickness of the PET crystals decreased as the annealing time in the melt state was increased.     

Morphological characterization during deformation of a poly(ether ester) thermoplastic elastomer by small-angle x-ray scattering

The scattering behavior of pre-drawn and annealed bristles of a highly deformable poly(ether ester) themoplastic elastomer based on poly(butylene terephthalate) as hard segments and poly(ethylene glycol) as soft segments in a ratio of 57/43 wt.-% is studied. Small-angle x-ray seattering measurements with an area detector are carried out on bristles with and without application of stress up to 195% relative deformation. Two-dimensional scattering patterns are used for morphological characterization of the sample.At small deformations one morphology peak is found, corresponding to a periodicity that changes affinely with deformation. The morphology of the smaple represents assemblies of mutually parallel crystalline lamellae, positioned perpendicular to the stretching direction both under and without stress. When macrodeformation increases a second peak appears, and a four-point pattern is observed in the relaxed state. In this intermediate deformation range coexisting morphologies contribute to the scattering. Additional contributions arise from lamellae, which are inclined to the stretching direction, as well as from lamellae, which are again perpendicular to the stretching direction, as a result of microfibril relaxation and loss of interfibrillar contacts. At large deformations the latter morphology dominates and the 2D-scattering pattern again shows a two-point character. A morphological model for this behaviour is discussed, where the break of interfibrillar contacts during deformation and the inhomogeneous stress field in the sample play an important role.Dedicated to the 65th birthday of Prof. E.W. Fischer Prof. Fischer was always a quide and patient teacher to us, he inspired our work with his intense interest and many valuable suggestions. We want to congratulate and thank him sincerely and extend our best wishes for the future.     

Biodegradation study of plasticised corn flour/poly(butylene succinate-co-butylene adipate) blends

Plasticised corn flour/poly(butylene succinate-co-butylene adipate) (PBSA) materials were prepared by extrusion and injection in order to study the impact of PBSA ratio on their physicochemical properties and biodegradability. Scanning electron microscopy observations showed that corn flour and PBSA are incompatible. Three types of morphology have been observed: (i) starch dispersed in a PBSA matrix, (ii) a “co-continuous-like” morphology of starch and PBSA, and (iii) PBSA dispersed in a starch matrix. As expected, the extent of plasticised corn flour starch hydrolysis by amylolytic enzymes decreased when the amount of PBSA increased. Addition of a lipase to hydrolyse PBSA ester bonds enhanced enzymatic hydrolysis of starch by amylolytic enzymes in materials where PBSA formed a continuous phase. This suggests that PBSA formed a barrier restricting the access of amylolytic enzymes to starch. This was consistent with aerobic and anaerobic biodegradation assays, which also showed lower biodegradability of materials containing a majority of PBSA.     

Distribution of nanoclay in a new TPV/nanoclay composite prepared through dynamic vulcanization

In this article distribution of nanoclay between the two phases of a new class of dynamically vulcanized TPV based on POE/EVA(Polyethylene octene elastomer/ethylene vinyl acetate copolymer) elastomers prepared with various amounts of organoclay (0.5, 1 and 3 wt%) using dicumyl peroxide (DCP) as vulcanizing agent by reactive melt blending process has been studied. Different specimens of POE and POE/EVA blend with and without clay were prepared. The effects of organoclay on mechanical properties, swelling kinetics, crystallinity, vulcanization characteristics, dynamic mechanical behaviour, electrical properties and morphology were studied. DMA and morphological analysis revealed the formation of a Thermoplastic vulcanizate. XRD analysis showed decrease in crystallinity on addition of EVA in POE matrix. However, morphological observation of the fractured surface suggested that the smaller EVA domain was quite uniformly distributed into the POE phase and the clay phase was predominantly dispersed in the EVA phase of the TPVs and 0.5% clay mainly improved the mechanical properties and elongation of the blends. Swelling characteristics, electrical properties and storage modulus were also improved with the clay in case of the blend containing higher EVA content which further supports the fact that nanoclay was preferably distributed in the more polar EVA phase.     

Morphology Evolution of Poly（vinylidene fluoride） Membranes during Supercritical CO2 Assisted Phase Inversion

A supercritical carbon dioxide（Sc CO2） assisted phase inversion was developed to produce microporous poly（vinylidene fluoride）（PVDF） membranes whose morphology characteristics arise from both liquid-liquid demixing and solid-liquid demixing（crystallization）. This result was confirmed by Fourier transform infrared spectroscopy（FTIR）, from which both α and β crystals were found. As revealed by contact angle experiment, the PVDF membranes prepared via Sc CO2 assisted phase inversion were more hydrophobic compared with the control membrane produced via conventional immersionprecipitation technique. In particular, the sample with 15 wt% PVDF prepared at 45 °C and 13 MPa exhibited a contact angle of 142°, which was mainly caused by the multilevel micro- and nano- structure. The effects of polyethylene glycol（PEG）, polyvinyl pyrrolidone（PVP） and lithium chloride（Li Cl） on the structures and crystal form were investigated. PVP promoted the formation of β phase crystal form, while PEG boosts the evolution of α phase. Li Cl restrained the crystallization degree of PVDF membrane under Sc CO2.