Interface/morphology relationships in polymer blends with thermoplastic starch

In this paper, the interface/morphology relationship in polyethylene/TPS blends prepared by a one-step extrusion process is examined in detail. Emulsification curves tracking the change in phase size with added quantity of PE-g-MA copolymer are used to identify the critical concentration required for saturation of the interface as well as to estimate the areal density of grafted copolymer chains at the interface. The level of glycerol content in the TPS is shown to lead to different emulsification behaviors. Dynamic mechanical analysis clearly shows a partial miscibility between glycerol and starch in the TPS with glycerol-rich and starch-rich peaks being clearly identified. This phase separation is more evident in the case of high glycerol levels in the TPS (>24% glycerol). Furthermore, the glycerol-rich peak decreases in intensity with added PE-g-MA graft copolymer. At high glycerol contents (>24% glycerol) in the TPS, a 20% thermoplastic starch-based binary blend with polyethylene can reach an elongation at break value as high as 200%. When also modified at the appropriate level with a PE-g-MA copolymer, this elongation at break further increases to 600%. However, at lower glycerol contents, the elongation at break is comparatively low at 20-50% even after the addition of PE-g-MA copolymer. We explain these results through a proposed double mechanism of interfacial modification between the HDPE matrix and the TPS dispersed phase. Under dynamic melt-mixing conditions, it is suggested that a small portion of the low molecular weight glycerol-rich phase tends to migrate to the HDPE-TPS interface as predicted by Harkins spreading theory. Once at the interface, this glycerol-rich outer layer is readily deformed by an applied stress and this stress is then transferred to the starch-rich phase due to their mutual partial miscibility. Added PE-g-MA copolymer initially reacts with the glycerol-rich outer layer but if the level of copolymer is high enough, it then reacts with the starch-rich phase via a classic interfacial modification protocol. Also, both the elongation at break and impact properties dramatically increase at a copolymer level associated with interfacial saturation. The above mechanism effectively explains all the emulsification and mechanical property observations.     

Polyethylene-octene elastomer/starch blends: miscibility,morphology and mechanical properties

In this paper, polyethylene-octene elastomer (POE) and starch blends were studied. The compatibility beyween POE and starch was improved by adding polyethylene-octene/maleic anhydride graft copolymer (POE-MA) as compatibilizer. The compatibilization reaction was followed by FTIR spectra. The morphology of the blends was investigated using scanning electron microscopy (SEM). It was found that the size of the starch phase increased with an increasing content of starch for the blends. The addition of POE-MA can lower the size of the starch phase in the POE matrix, and this was due to the formation of an ester carbonyl function group by the chemical reaction between the anhydride groups and hydroxyl groups on starch. This was reflected in the mechanical properties of the blends, the addition of POE-MA compatibilizer can improve the mechanical properties of POE/starch blends. The thermogravimetric analysis of POE/starch blends was also conducted.     

Linear viscoelastic properties of olefinic thermoplastic elastomer blends: melt state properties

The linear viscoelastic properties of two types of olefinic thermoplastic elastomer blends were studied using dynamic rheology. The first type consists of a blend of PP, SEBS and oil and has a co-continuous morphology. The second type consists of vulcanised EPDM particles dispersed in a PP matrix. The dynamic rheological behaviour of the blends is a weighted contribution of the properties of the two individual phases. In both blend types, the storage modulus at low frequencies can be correlated to the properties and morphology of the elastomer phase. With increasing PP or oil content in the blend the value of the modulus at low frequencies are reduced. The mechanical models of Coran and Veenstra are able to describe the dynamic moduli. An additional parameter was included to determine the oil concentration in the two phases. The model parameters are correlated to the composition and the morphology.     

Morphology and finite strain rheologyof NBR/TPU blends

Due to orientational and dispersional interactions between molecules in polar polymer blends, such as NBR/TPU, secondary molecular networks are formed, which, despite their weakness, essentially affect rheological properties of the blends. Being highly susceptible to strain and temperature changes, the secondary networks under such conditions undergo breakdown, causing changes in blends' rheological characteristics. Particularly suitable method for tracking such network breakdown is by measuring the blends' dynamic mechanical functions at different strains and temperatures. For elucidation of these measurements a model is chosen, analysing a secondary network breakdown by statistical mechanics, whose final result is strain, temperature and compositional dependence of the blends' dynamic mechanical functions. Along with the measurements', the chosen model, originally devised to study rheological properties of carbon black filled rubbers, also provides means for quantitative characterization of secondary networks in polar polymeric systems.     

High performance modified thermoplastic starch/linear low‐density polyethylene blends in one‐step extrusion

In this study, the morphology and the mechanical properties of thermoplastic starch (TPS)/linear low‐density polyethylene (LLDPE) blends prepared by one‐step and two‐step extrusion processing conditions were contrasted. In the presence of citric acid (CA), the compatibility of TPS/PE blends were proved to transfer to a high continuous dispersion in one‐step extrusion process by scanning electron microscopy analysis. By increasing the interaction between two phases, the mechanical properties of the blends were markedly improved, even reached the levels of the conventional plastics. The rheological study proved that the viscosity (η) of TPS and TPS/PE blends were both decreasing with increase in the content of CA at the same temperature, which ascribed to the acidity of CA was propitious to fragmentation and dissolution of cornstarch granules, deteriorated the chain entanglement in starch, and weakened the interaction of starch molecules. Both FTIR spectroscopy and thermal properties analysis of TPSs and TPS/PE blends showed that the interactions between starch and plasticizer became stronger in the presence of CA. POLYM. COMPOS. 28:89–97, 2007. © 2007 Society of Plastics Engineers     

Interfacially compatibilized LDPE/POE blends reinforced with nanoclay: investigation of morphology,rheology and dynamic mechanical properties

Morphological, melt rheological and dynamic mechanical properties of low-density polyethylene (LDPE)/ethylene–octene copolymer (POE)/organo-montmorillonite (OMMT) nanocomposites, prepared via melt compounding were studied. The XRD traces indicated different levels of intercalated structures for the nanocomposites. Addition of a compatibilizer (PE-g-MA) improved the intercalation process. TEM results revealed existence of clay layers in both phases but they were mainly localized in the elastomeric POE phase. Addition of 5 wt% OMMT to the LDPE/POE blend led to reduction in the size of the elastomer particles confirmed by AFM. The complex viscosity and storage modulus showed little effect of the presence of the clay when no compatibilizer was added. As the extent of exfoliation increased with addition of compatibilizer, the linear viscoelastic behavior of the composites gradually changed specially at low-frequency regions. The interfacially compatibilized nanocomposites with 5 wt% OMMT had the highest melt viscosity and modulus among all the studied nanocomposites and blends. Also, this particular composition showed the best improvement in dynamic storage modulus. The results indicated that clay dispersion and interfacial adhesion, and consequently different properties of LDPE/POE/clay nanocomposites, are greatly affected by addition of compatibilizer.     

Compatible thermoplastic starch/polyethylene blends by one‐step reactive extrusion

In the presence of dicumyl peroxide (DCP), the thermal plasticization of starch and its compatibilizing modification with polyethylene was accomplished by one‐step reactive extrusion in a single‐screw extruder at the same time. Because of the formation of polyethylene‐graft‐maleic anhydride (PE‐g‐MAH) during the extrusion, it was used as the compatibilizer between the thermoplastic starch and polyethylene. The blending samples were characterized by means of thermogravimetric analysis (TGA), scanning electron microscopy (SEM), dynamic thermal mechanical analysis (DTMA) and Fourier‐transform infrared (FTIR) analysis. The experimental results showed that in the presence of DCP the addition of MAH improved the mutual dispersion of molecules in thermoplastic starch and polyethylene. From TGA, we concluded that the thermal stability of the blends with MAH was improved compared with the blends without MAH. The DTMA and FTIR results indicated that, with the addition of MAH, the compatibility of molecules between thermoplastic starch and polyethylene in the blends was improved. Copyright © 2004 Society of Chemical Industry     

Rheological behavior of thermoset/thermoplastic blends during isothermal curing: Experiments and modeling

The evolution of the viscoelastic properties of a molten thermoplastic/thermoset system during the course of the isothermal polymerization of the thermoset precursors has been investigated and modeled. Such systems are initially homogenous and phase separate upon polymerization of the monomers. In the present study, atactic polystyrene (85 and 60 wt%) is blended to a stoichiometric mixture diglycidyl ether of bisphenol A with 4,4′-methylenebis(2,6-diethylaniline). During the polymerization, polystyrene becomes the thermoplastic-rich matrix and an epoxy-rich dispersed phase appears. Both phases experience changes in their composition and viscoelastic properties. A rheokinetic model is proposed to take into account four contributions to the viscoelastic behavior: progressive deplastification of the polystyrene matrix involving a modification of the glass transition and thus of free volume, dilution of the network of entanglements of the matrix by the non yet converted low molar weight molecules, emulsion behavior after the separation of the epoxy-rich phase and finally interparticular interactions being assimilated to a mechanical percolation. Provided that the glass transition temperature of the matrix and the dynamic moduli of the neat components are known, the changes in the viscoelastic behavior of the system with time can be predicted with no ad hoc parameter and model calculations are in good agreement with the experimental data.     

A comparative study on the effect of different reactive compatibilizers on injection-molded pieces of bio-based high-density polyethylene/polylactide blends

The present study reports on the development of binary blends consisting of bio-based high-density polyethylene (bio-HDPE) with polylactide (PLA), in the 5–20 wt % range, prepared by melt compounding and then shaped into pieces by injection molding. In order to enhance the miscibility between the green polyolefin and the biopolyester, different reactive compatibilizers were added during the melt-blending process, namely polyethylene-grafted maleic anhydride (PE-g-MA), poly(ethylene-co-glycidyl methacrylate) (PE-co-GMA), maleinized linseed oil (MLO), and a combination of MLO with dicumyl peroxide (DCP). Among the tested compatibilizers, the dual addition of MLO and DCP provided the binary blend pieces with the most balanced mechanical performance in terms of rigidity and impact strength as well as the highest thermal stability. The fracture surface of the binary blend piece processed with MLO and DCP revealed the formation of a continuous structure in which the dispersed PLA phase was nearly no discerned in the bio-HDPE matrix. The resultant miscibility improvement was ascribed to both the high solubility and plasticizing effect of MLO on the PLA phase as well as the crosslinking effect of DCP on both biopolymers. The latter effect was particularly related to the formation of macroradicals of each biopolymer that, thereafter, led to the in situ formation of bio-HDPE-co-PLA copolymers and also to the development of a partially crosslinked network in the binary blend. As a result, cost-effective and fully bio-based polymer pieces with improved mechanical strength, high toughness, and enhanced thermal resistance were obtained. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47396.     

Elaboration of PEG/PA66 blends in a twin-screw batch-type mini-extruder: Process study and modelling

This paper deals with the development of the morphology in polyethylene glycol (PEG) and polyamide 66 (PA66) immiscible blends exhibiting an extremely low viscosity ratio (η_PEG/η_PA66=3-4×10^-5). These materials were obtained by melt mixing, under different operating conditions, using a twin-screw batch-type DSM mini-extruder.Scanning electron microscopy, followed by quantitative image analysis was used to determine PEG particles size distribution (PSD) as a function of blends composition and screw rotation speed. Experiments carried out with two mixing time (5 and 10 min) showed no significant difference of PSD. So, to avoid thermal degradation of the products, the mixing time was set up at 5 min for all experiments. The influence of PEG concentration and screw rotation speed on PSD appeared to be similar to that obtained in a previous study for the same blends elaborated in a Haake internal mixer. The results clearly showed that the average particle diameters decreased as screw rotation speed increased and as PEG concentration decreased. However, this decrease is less important using the twin-screw batch-type mini-extruder with which the particle sizes are smaller. The particles sizes were then correlated to blend composition, shear rate and viscosity ratio owing to an extension of Serpe's model. The unknown parameters of the corresponding model were estimated on the basis of experimental data. This enabled then to predict with a good precision the influence of the process operating conditions on the morphology of the dispersed phase.     

Morphology and tensile properties of high-density polyethylene/natural rubber/thermoplastic tapioca starch blends: The effect of citric acid-modified tapioca starch

The effect of citric acid on the tensile properties of high density polyethylene (HDPE)/natural rubber (NR)/thermoplastic tapioca starch (TPS) blends was investigated. The ratio between HDPE/NR was fixed at 70/30 and used as the matrix system. TPS loadings, after modification with citric acid (TPSCA) and without modification (TPS), were varied from 0 to 30 wt %. The morphologies and tensile properties of HDPE/NR blends were evaluated as a function of TPS loadings. The tensile strength, Young's modulus, and elongation at break were found to decrease with increasing TPS loading. However, a slight improvement in the tensile strength of HDPE/NR/TPSCA blends at 5 and 10 wt % TPS loadings were observed. TPS can be partly depolymerised to produce a low viscosity product when processed with citric acid. TPS with low viscosity can easily disperse in the thermoplastic natural rubber (TPNR) system and reduce the surface tension at the interphase of TPS-HDPE/NR as shown by scanning electron microscopy (SEM). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Morphology development by reactive compatibilisation and dynamic vulcanisation of nylon6/EPDM blends with a high rubber fraction

Binary nylon6/rubber blends with 50 or 60 weight percent of an EPDM rubber exhibit co-continuous morphologies and thereby relatively poor mechanical properties. This paper describes methods to develop nylon6/EPDM blends with a high amount of finely dispersed rubber particles embedded in a nylon matrix. Using a suitable compatibiliser and by slightly crosslinking the rubber phase during melt-mixing, it was possible to disperse up to 60 wt% rubber in the nylon matrix and to improve the mechanical properties markedly. These materials are called thermoplastic vulcanisates and exhibit good elastic properties with a thermoplastic processability. The influence of the compatibiliser, the crosslinking agent and the viscosity ratio rubber/thermoplastic on the blend phase morphology is investigated using transmission electron microscopy. It was found that the viscosity ratio rubber/nylon plays a crucial role in order to achieve a nylon6/rubber TPV with a fine rubber dispersion. The viscosity of the nylon phase should be low enough to shift the phase inversion towards higher rubber content. On the other hand, if the viscosity of the nylon is too low, a coarse blend morphology was achieved resulting in poor mechanical properties.     

Morphology and rheological properties of compatibilized low‐density polyethylene/linear low‐density polyethylene/thermoplastic starch blends

Morphology and rheological properties of low‐density polyethylene/linear low‐density polyethylene/thermoplastic starch (LDPE/LLDPE/TPS) blends are experimentally investigated and theoretically analyzed using rheological models. Blending of LDPE/LLDPE (70/30 wt/wt) with 5–20 wt % of TPS and 3 wt % of PE‐grafted maleic anhydride (PE‐g‐MA) as a compatibilizer is performed in a twin‐screw extruder. Scanning electron micrographs show a fairly good dispersion of TPS in PE matrices in the presence of PE‐g‐MA. However, as the TPS content increases, the starch particle size increases. X‐ray diffraction patterns exhibit that with increase in TPS content, the intensity of the crystallization peaks slightly decreases and consequently crystal sizes of the blends decrease. The rheological analyses indicate that TPS can increase the elasticity and viscosity of the blends. With increasing the amount of TPS, starch particles interactions intensify and as a result the blend interface become weaker which are confirmed by relaxation time spectra and the prediction results of emulsion Palierne and Gramespacher‐Meissner models. It is demonstrated that there is a better agreement between experimental rheological data and Coran model than the emulsion models. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44719.     

From microstructure to mechanical properties of compatibilized polylactide/thermoplastic starch blends

Bio‐degradable polymer blends of polylactic acid/thermoplastic starch (PLA/TPS) were prepared via direct melt blending varying order of mixing of ingredients fed into the extruder. The effect of interface interactions between PLA and TPS in the presence of maleic anhydride (MA) compatibilizer on the microstructure and mechanical properties was then investigated. The prepared PLA/TPS blends were characterized by scanning electron microscopy, differential scanning calorimetry (DSC), tensile, and rheological measurements. Morphology of PLA/TPS shows that the introduction of MA into the polymer matrix increases the presence of TPS at the interface region. DSC results revealed the reduction of glass transition temperature of PLA with contributions from both TPS and MA. The crystallization temperature was decreased by the addition of MA leading to reduction of overall crystallization of PLA/TPS blend. The mechanical measurements show that increasing MA content up to 2 wt % enhances the modulus of PLA/TPS more than 45% compared to the corresponding blends free of MA compatibilizer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44734.     

Novel nanostructured polyamide 6/fluoroelastomer thermoplastic elastomeric blends: Influence of interaction and morphology on physical properties

Novel polyamide 6 (PA6)/fluoroelastomer nanostructured thermoplastic elastomeric blends were developed in the present work. The influence of interaction between the components and morphology on physical properties of the blends was analyzed. Scanning electron microscopy and atomic force microscopy studies, solubility and theoretical analysis of complex modulus clearly indicated that PA6 was the continuous matrix in which fluorocarbon elastomer was present in nanoscale. Low torque ratio (0.34) of rubber/plastic, high mixing speed and long mixing time had an important role in developing the nanostructured morphology of the blend. Tensile strength of the thermoplastic elastomer was about 39.0 MPa which was much higher than that reported earlier and showed significant improvement with increasing PA6 content. Large shifting of the glass transition temperature of the rubber and the plastic phases towards the lower temperature compared to those pristine polymers was also observed. The above properties were explained with the help of interaction between the components and morphology.     

High performance polylactic acid/thermoplastic polyurethane blends with in-situ fibrillated morphology

As an environment-friendly polyester, polylactic acid (PLA) shows great potential market value. While it still faces some obstacles in large-scale practical application due to its brittleness. In this work, a novel strategy to improve the toughness of polylactic acid is developed. By adjusting processing temperature during the melt-blending process, thermoplastic polyurethane/poly (D-lactic) acid/poly (L-lactic) acid (TPU/PDLA/PLLA) ternary blends with different morphology are obtained. The experimental results show that the TPU in ternary blends formed a fibrillated micro-morphology, and the interfacial compatibility between the components is improved when the processing temperature is adjusted to 200°C. Under the synergistic action of in-situ fibrillated TPU and stereocomplex (SC) crystals, the toughness of the ternary blends is improved significantly without sacrificing its own tensile strength. The maximum value of tensile strength, elongation at break, and fracture work of ternary blends are 61.9 MPa, 23.5%, and 1038.9 kJ/m³, respectively. In addition, the melt strength of ternary blends was significantly improved, which is a benefit to their processing application.     

Reactive compatibilizer precursors for LDPE/PA6 blends. III: ethylene-glycidylmethacrylate copolymer

The effectiveness of a commercial ethylene-glycidylmethacrylate copolymer (Lotader GMA AX 8840) as a compatibilizer precursor (CP) for blends of low density polyethylene (LDPE) with polyamide-6 (PA) has been evaluated by an investigation of the thermal properties and the morphology of binary (LDPE/CP and PA/CP) and ternary (LDPE/PA/CP) blends, as well as by solvent fractionation experiments. It has been demonstrated that the epoxy groups of the CP react quite easily, during melt blending, with both the amine and the carboxyl end groups of PA to give CP-g-PA copolymers, which, depending on the relative amounts of PA and CP, may be partially cross-linked. The composition of the graft copolymers has been approximately determined by gravimetric and calorimetric measurements. The compatibilizing efficiency of the CP employed in this work has been found to be comparable to that of the ethylene-acrylic acid copolymers, and lower than that of a maleic anhydride-functionalized polyethylene, which had been used in previous works.     

In situ compatibilization of polypropylene–polyethylene blends: a thermomechanical and spectroscopic study

Polypropylene (PP) and low density polyethylene (LDPE) were melt blended in proportions of 75/25, 50/50 and 25/75 w/w, respectively. Poly(propylene-g-maleic anhydride) (PP-g-MA) with 0.8 mol% maleic anhydride content and poly(ethylene-co-vinyl alcohol) (EVAL) with 7.5 mol% vinyl alcohol content were added at a 50/50 w/w proportion as in situ reactive compatibilizers. Four series of compatibilized blends were produced containing 2.5, 5, 10 and 20 wt% compatibilizer in the final blend. The compatibilization reaction was followed by a torque increase during mixing and by FTi.r. spectroscopy. A notable improvement in tensile strength, elongation at break and impact strength was observed for all blends after compatibilization and, in particular, for the blends containing 10 wt% compatibilizer. Scanning electron microscopy (SEM), aided by micro-Raman spectroscopy, was used for investigating the morphology of the blends.     

Toughening of polyethylene terephthalate/amorphous copolyester blends with a maleated thermoplastic elastomer

The toughening of polyethylene terephthalate (PET)/amorphous copolyester (PETG) blends using a maleic anhydride grafted mixture (TPEg) of polyethylene‐octene elastomer and a semicrystalline polyolefin plastic (60/40 by weight) was examined. The TPEg was more effective in toughening PETG than PET, although the dispersion qualities of the TPEg particles in PET and PETG matrices were very similar. At the fixed TPEg content of 15 wt %, replacing partial PET by PETG resulted in a sharp brittle‐ductile transition when the PETG content exceeded the PET content. Before the transition, PET/PETG blends were not toughened with the TPEg of 15 wt %, whereas after the transition, the PET/PETG blends with 15 wt % of TPEg, similar to the PETG/TPEg (85/15) binary blend, maintained a super‐tough level. The impact‐fractured surfaces of the PET/PETG/TPEg blends were also evaluated. When PETG content was lower than PET content, the ternary blend showed a brittle feature in its impact‐fractured surface, similar to the PET/TPEg (85/15) binary blend. While PETG content exceeded PET content, however, the impact‐fractured surface of the ternary blend was very similar to that of PETG/TPEg (85/15) binary blend, exhibiting intensive cavitation and massive matrix shear yielding, which were believed to be responsible for the super‐tough level of the blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 797–805, 2003     

Enhancement of pro‐degradant performance in polyethylene/starch blends as a function of distribution

The effect of pro‐degradant distribution in polyethylene (PE)/starch blends on ultraviolet (UV) photo‐oxidative degradation was investigated. Two kinds of pro‐degradants, Fe and Co‐based, were used in this study. The distribution of pro‐degradants in the different phases was varied by a dual step process using a side‐feed on a reactive extruder. The variation in mechanical properties and evaluation of carbonyl groups by FTIR were conducted to investigate the effect of degradation following exposure to UV photo‐oxidative degradation. It was found that the variation in mechanical properties was higher when the pro‐degradants were distributed in the PE phase. The concentration of carbonyl groups increased as a function of UV exposure, and the concentration of carbonyl groups was higher when the pro‐degradants were distributed in the PE phase. Micro‐cracking was observed on the interface between starch and PE after adding the pro‐degradants. When the pro‐degradants were distributed in high‐density polyethylene (HDPE) phase, the micro‐cracks mainly appeared in HDPE matrix, and the density of micro‐crack was higher. In general, the function of the pro‐degradants in PE/starch blends was enhanced when their distribution was varied within HDPE phase. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013