A novel model is presented for predicting the phase selective filler localization in an equilibrium state for ternary rubber blends of SBR, NBR, and NR. It is based on surface tension data of the rubber components and the filler. Phase‐selective filler localization in ternary rubber blends is determined experimentally by means of FTIR spectroscopy on the basis of the wetting concept. It is found that by preparation of ternary blends with certain silica loadings, pre‐mixed in each blend phase using the masterbatch technology, silica transfer processes between blend phases take place until the equilibrium filler distribution is reached. The sequence of the silica transfer processes can be explained by taking into consideration the formation of a phase‐in‐phase morphology of the ternary blend.
Recycling of thermoplastic wastes consisting of PE/PP/PS/HIPS blends was investigated by using SEBS/EPR and SBR/EPR as compatibilizers. The effect of the binary compatibilizer systems and processing conditions on the mechanical properties and morphology of the blends are discussed. The SEBS/EPR system allowed blends with better mechanical properties to be obtained than the SBR/EPR system; this was attributed to the chemical structure similarity between compatibilizers and recycled materials. The optimal conditions for processing of the recycled thermoplastics (blends) were found to be 190 °C, 14 min of processing time and 3.5 wt.‐% of compatibilizer. The morphology and mechanical properties of the blends were discussed using theoretical phase diagrams and models proposed in the literature, and good agreements between these properties were found.
Liquid‐crystalline epoxy thermosets were prepared by adding M1 into DGEBA/DDM blends. M2 was added to DGEBA/DDM to produce thermosets for comparison. The influences of the concentration and chemical structure on the mechanical and thermal properties were investigated systematically. The M1 /DGEBA blends possessed increased rubbery plateau modulus, higher glass transition temperatures, and lower tan δ. The use of small amounts of M1 may improve the mechanical properties greatly. Izod notched impact strength could be enhanced by 55% by addition of 2% M1 compared to unmodified DGEBA blends. Extremely rough and highly deformed fracture surface could be obtained in the M1 /DGEBA blends. M1 /DGEBA blends also exhibited excellent thermal properties.
The preparation of nanofibrillar composite (NFC) materials using single‐polymer nanofibrils as starting materials is described. Such a possibility is offered by (i) the concept of polymer/polymer NFCs, which have recently been manufactured and represent a further development in the field of microfibril‐reinforced composites, and (ii) the opportunity to isolate neat nanofibrils through selective dissolving of the second blend component. The resulting nanofibrillar single‐polymer composites are characterized by superior mechanical properties (the tensile modulus and strength are improved up to 350%), competing with glass‐fiber‐reinforced PET.
In this study, the sol‐gel transition temperature of a thermosensitive chitosan system was measured using SAOS, in‐real time FTR and multi‐frequency SAOS excitation. From FT analysis, we found that the intensity of the harmonics stayed constant while the chitosan system remained in the solution state, while it increased passed the gelation point. Multi‐frequency SAOS excitation was also carried out using a summation function of sine waves that allowed performing the measurements in the LVR. This last technique could determine the unique (frequency independent) critical sol‐gel transition temperature, and was found to be less tedious than the application of the traditional Chambon and Winter's method.
We report a ternary system of poly(styrene‐co‐acrylonitrile) (SAN), poly(vinyl chloride) (PVC), and multi‐walled carbon nanotube (MWCNT) composites prepared by both a solution blending method and the SOAM. The MWCNT content in the composites was optimized by both TGA and mechanical characterization of binary mixtures of SAN/MWCNT and PVC/MWCNT composites. The dispersion of MWCNTs in the miscible SAN/PVC blends was characterized by FT‐Raman spectroscopy, FE‐SEM, and FE‐TEM. The distribution of MWCNTs in the SAN/PVC blends was examined in terms of their wetting coefficients and minimization of the interfacial energy. Composites prepared using the SOAM method showed superior physical properties to the SAN/PVC blends and SAN/PVC/MWCNT composites prepared using the solution blending method.
Polyhydroxyalkanoate (PHA) and poly(propylene carbonate) (PPC) are blended in order to investigate their mutual contributions in terms of functional properties. A wide range of blend composition is processed through extrusion from dry blends. Droplet‐matrix morphology is observed for all samples. Thermal investigations reveal the PPC effect on the PHA crystallization process with a decrease and broadening of the crystallization temperature window and on the depression of its glass transition temperature. This investigation also confirms the as yet un‐reported non‐miscibility of this kind of blend. However, a slight phase interaction is expected since thermal behavior of PHA is impacted. The fragile behavior of PHA is balanced by the high ductility of PPC. The weak strain at break of PHA can thus be increased by up to 200% although a significant amount of PPC is needed to start modifying this property. Stress at break and modulus are linearly decreased from pure PHA to pure PPC values. PPC also acts as an impact modifier for PHA. In terms of barrier properties, PHA brings a large contribution even at low content to the initially high oxygen and water vapor permeability of PPC.
The effect of OMLS incorporation on the thermal properties of PET/LCP blends is studied. Pure and OMLS‐modified PET/LCP blends were prepared by melt‐extrusion using twin‐screw extruder. The morphological analyses of PET/LCP blends show that OMLS addition enhances the phase‐separated structure of the pure blend. A detailed study on the thermal properties of the pure and OMLS‐modified PET/LCP blends were carried out by means of DSC in both conventional and modulation modes. Results show a complex melting behaviour comprises of successive melting and re‐crystallisation. Finally, non‐isothermal crystal‐growth kinetics of pure and OMLS‐modified blends were investigated.
Spherical silica nanoparticles were infused into nylon‐6 and drawn into filaments through a melt‐extrusion process. The idea was to improve the strength and stiffness of the resulting filaments by utilizing the interactions between the nanoparticles and the polymer. The focus was to increase the fracture strain of the filaments, as this had not been possible earlier with the infusion of carbon nanotubes. It has been observed that with the infusion of silica nanoparticles, the strength and Young's modulus of the nylon filament can be enhanced in the 28 to 36% range without any loss of fracture strain. The source of this improvement has been traced to the formation of stronger amide and carbonyl bonds, nucleated by the presence of SiO2 nanoparticles during polymerization. Moreover, calculations based on basic theories of inclusions show that the Young's modulus of the nanophased filament is within 5% of the upper bound predicted by the micromechanical theory.
The effect of CO2‐induced crystallization on the mechanical properties, in particular the yield and the ultimate stresses, of polyolefins is studied. PP and SEBS copolymer blends are used as examples and foamed after sorption of CO2 at temperatures below Tm. CO2 sorption thickens the crystalline lamellae and consequently increases Tm from 160 to 178 °C for both pure PP and PP/SEBS blend systems. Foams with an average cell size smaller than 250 nm retain the ultimate stress at the level of the polymer before foaming, even without the effect of CO2‐induced crystallization. Including CO2‐induced crystallization, the yield and the ultimate stresses of the foam can be improved by 30 and 50% over solid PP and by 22 and 40%, for solid PP/SEBS blends, respectively.
Microcellular biodegradable polymer foam with an open porous structure was prepared from amorphous poly‐L,D ‐lactic acid (PL ,D LA) blended with polystyrene (PS), or polymethyl methacrylate (PMMA). The blends were prepared by polymerizing either styrene or methyl methacrylate (MMA) in a PL ,D LA matrix. The styrene and MMA monomers are good cell‐opening agents and constituents for an IPN. Pressure‐quench batch foaming was conducted using carbon dioxide as a foaming agent at 80 °C under 10 MPa. The effects of monomers and a cross‐linking agent on the foamability and OCC were investigated. Manipulation of the monomer and the cross‐linking agent concentrations was able to change the viscoelasticity and partial miscibility of the blend and control the cell size at the micron scale as well as open pore content in the range of 20–90%.
Summary: Novel poly(cyclotriphosphazene‐co‐sulfonyldiphenol) microtubes were successfully prepared via one‐pot synthesis using special templates generated in situ during the polymerization. The templates could be easily removed by dissolution in water. This approach overcame the multi‐step nature of general template methods. The as‐synthesized microtubes were 1–3 µm in width, about 100 µm in length and contained hexagon‐shaped channels. IR and NMR spectroscopies confirmed the covalently crosslinked chemical structure of the polymer tubes, and the tubes are thus mechanically and thermally stable. The polymer microtubes are of interest for use as chemical or biological sensors, controlled release and delivery of drugs, tissue engineering materials, absorbants and many other microscale investigations.
SEM images of triethylamine hydrochloride crystals produced in situ during formation of the tubes (left) and the polymer microtubes (right). 相似文献
An improvement to a previously published suspension polymerization process for the production of spherical core/shell PVAc/PVA particles is described. To increase the settling time of the beads in the suspension, an expansion stage was introduced. The core/shell structure was obtained through the partial hydrolysis of the PVAc. The particle density was manipulated through addition of a solvent during the suspension polymerization stage and posterior expansion of the polymer beads obtained at the end of the process. This technique allows for effective reduction of the density of the final polymer beads. The expansion stage exerts also a beneficial effect on particle drying, avoiding particle aggregation during post‐polymerization processing of the polymer beads.
A new technique for design and preparation of self‐reinforced starch films is introduced. The films were based on a high‐amylose corn starch that was chemically modified in different ways. Hydroxypropylation was used to decrease gelatinization temperature and improve processability. The reinforcing component consisted of cross‐linked starch granules, where the crosslinking increased granule thermal stability and moisture resistance. Distribution of the cross‐linked starch was imaged by CLSM, and the matrix/particle interface was studied by SEM. Modulus and tensile properties of the starch film were increased by about 30 and 20%, respectively, after addition of rigid cross‐linked starch particles. A perfect interface between matrix and reinforce agent was obtained.
The solid and thermally instable azoinitiators V‐65 and VR‐110 were embedded within a polymer particle by using the miniemulsion process and afterwards quickly decomposed by thermal treatment below the glass temperature of the polymer. The resulting nitrogen gas overpressure inside the particles leads to a disruption of the polymer particle and a possible sudden release of encapsulated substances. It is shown, by electron microscopic measurements, that the number of burst particles correlates with the applied temperatures as well as the heating time. The surface deformation could be verified by scanning electron microscope analyses.
A “green” processing method, dual‐melt extrusion, was used to prepare thermoplastic starch/montmorillonite nanocomposites without organic reactions in the solution. XRD demonstrates that sorbitol enlarged the interlayer distance of MMT during the first step. MMT‐sorbitol, formamide and starch were used to obtain TPS/MMT nanocomposites in the second step. XRD and TEM reveal that TPS intercalated the layers of MMT. With increasing MMT content, improvements in thermal stability, tensile strength, Young's modulus and energy break, and a slight decrease of elongation at break, appeared. The effect of water content on the tensile strength and elongation at break was also studied.
Sunflower oil‐based HBTPU/Ag and LTPU/Ag nanocomposites have been prepared by in situ catalytic reduction of a silver salt. The virgin polymer and their nanocomposites are soluble in various polar organic solvents and amenable for both solution‐casting and hot pressing. XRD, TEM, and UV spectroscopic analyses ascertained well‐dispersed, narrow‐sized Ag nanoparticles. Tensile testing, dynamic mechanical, thermogravimetric, and DSC analyses showed desirable mechanical and thermal features with improvement upon incorporation of Ag nanoparticles and the presence of a hyperbranched component in the nanocomposites. RSM has been used to evaluate the catalytic efficacy of the nanocomposites.
Oriented precursors of MFCs consisting of HDPE and PA6 or PA12 are studied during strain‐controlled slow load‐cycling. In the PA6‐containing blends a strongly retarded nanostrain response is detected. Compatibilization induces nanostrain heterogenization. Stress fatigue is lower in the PA12 blends, but hardly decreased by the compatibilizer. Selective migration of the compatibilizer into a disordered semi‐crystalline fraction of the HDPE matrix can explain the findings. The semi‐crystalline HDPE entities in PA6 blends appear more disordered than in PA12‐blends. An analysis of the HDPE nanostructure evolution during cycling reveals epitaxial strain crystallization. Uncompatibilized PA6 blends cycled about high pre‐strain show plastic flow but nanoscopic shrinkage in the semi‐crystalline stacks.
The effect of organically modified clay on the morphology and properties of poly(propylene) (PP) and poly[(butylene succinate)‐co‐adipate] (PBSA) blends is studied. Virgin and organoclay modified blends were prepared by melt‐mixing of PP, PBSA and organoclay in a batch‐mixer at 190 °C. Scanning electron microscopy studies revealed a significant change in morphology of PP/PBSA blend in the presence of organoclay. The state of dispersion of silicate layers in the blend matrix was characterized by X‐ray diffraction and transmission electron microscopic observations. Dynamic mechanical analysis showed substantial improvement in flexural storage modulus of organoclay‐modified blends with respect to the neat polymer matrices or unmodified blends. Tensile properties of virgin blends also improved in the presence of organoclay. Thermal stability of virgin blends in air atmosphere dramatically improved after modification with organoclay. The effect of organoclay on the melt‐state liner viscoelastic properties of virgin blends was also studied. The non‐isothermal crystallization behavior of homopolymers, virgin, and organoclay‐modified blends were studied by differential scanning calorimeter. The effect of incorporation of organoclay on the cold crystallization behavior of PP/PBSA blends is also reported.
