The influence of boehmite crystallite sizes, varied between 10 and 60 nm, was studied with respect to the morphology development, crystallization behavior and mechanical properties of the boehmite‐based iPP nanocomposites. The nanometer‐scaled boehmites were formed during twin‐screw melt extrusion of iPP at 200 °C. Even in the absence of polymer compatibilizers, the boehmites, obtained from Sasol's process, enabled very effective deagglomeration and in‐situ dispersion of nanoboehmites. With increase in boehmite crystallite size it was possible to improve simultaneously stiffness and impact strength of iPP. As evidenced by means of DSC, POM and WAXS measurements, the deagglomerated nanoboehmites nucleated crystallization of poly(propylene)'s α‐modification.
The effects of nucleobases, especially uracil, on the nonisothermal and isothermal crystallization, melting behavior, spherulite morphology, and crystalline structure of bio‐based and biodegradable PLLA are studied. The melt‐ and cold‐crystallization rates of PLLA increase with increasing uracil loading. The melting behavior of nonisothermally melt‐ and cold‐crystallized PLLAs depends on the uracil content. The isothermal crystallization kinetics is analyzed based on an Avrami model. The incorporation of uracil changes the t1/2/Tc profile of PLLA due to the more distinct heterogeneous nucleation effects at small supercooling. The crystalline structure of PLLA is not affected by uracil presence. The nucleation density increases and the spherulite size decreases by uracil incorporation.
PBS is partially crosslinked by using DCP as an initiator. A low gel fraction (<30 wt%) and low crosslink density of the partially crosslinked PBS are obtained at a DCP content of <0.5 wt%. Consequently, the partially crosslinked PBS retains both its processability and its crystallinity. The overall crystallization rate of the PBS is enhanced by partial crosslinking as evidenced by a considerable increase in crystallization temperature (Tc). Meanwhile, the mechanical properties of PBS are significantly improved by the partial crosslinking. The structure/property relationships of the partially crosslinked PBS are explored.
The present study is aimed to investigate the effect of multiple extrusions of iPP/WF composites with and without EBAGMA used as compatibilizer. The degradation induced by the recycling processes was evaluated through changes in molecular structure, morphology, rheology, thermal and mechanical properties. The results showed that after six cycles, the presence of WF imparts stability to the composite materials. This effect was enhanced for the compatibilized samples. Further, SEM revealed better dispersion of the WF in the matrix. In contrast, it was confirmed that after the first recycling, both the molecular weight and the properties of PP drastically decreased due to chain scission resulting from degradation.
The fractional crystallization kinetics and phase behavior of PEO with different molecular weights (MWs) in its miscible crystalline/crystalline blends with PBS are studied. Both fractional crystallization kinetics and phase segregation of PEO in PBS/PEO blends are dramatically influenced by its MW. PEO with a medium MW (20 kDa) shows a significant fractional crystallization in the blends with PBS crystallized at a high TIC,PBS, which, however, is dramatically depressed in the blends with a very low or high MW of PEO. This indicates that the PEO component with a medium MW is more ready to segregate into the interlamellar region of PBS crystals than those with a very low or high MW. The MW‐dependent fractional crystallization kinetics and phase segregation of PEO component in the PBS/PEO blends are discussed.
The effects of crystallization temperature of PBS (TIC,PBS) on the fractional crystallization, phase segregation, and crystalline morphology of PEO in their miscible crystalline/crystalline blends are investigated. The crystallization kinetics and phase segregation of PEO are considerably influenced by TIC,PBS. A higher TIC,PBS results in the crystallization of PEO at an extremely large degree of supercooling and may facilitate the segregation of PEO within the interlamellar regions of PBS. At a high TIC,PBS (e.g., 95 °C), the long period, thickness of amorphous and crystalline layers of PBS increase upon blending with PEO. The TIC,PBS dependence of phase segregation of the PEO component is discussed from a thermodynamic as well as a kinetic perspective.
A comparative study of the preparation and properties of composites of PCL with cellulose microfibres (CFs) containing butanoic‐acid‐modified cellulose (CB) or PCL grafted with maleic anhydride/glycidyl methacrylate as compatibilizers, is reported. The composites are obtained by melt mixing and analyzed using SEM, DSC, TGA, XRD, FT‐IR, NMR and tensile tests. An improved interfacial adhesion is observed in all compatibilized composites, as compared to PCL/CF. The crystallization behavior and crystallinity of PCL is largely affected by CF and CB content. Composites with PCL‐g‐MAGMA display higher values of tensile modulus, tensile strength and elongation at break.
The effects of varying concentrations of incorporated PDLA on the acceleration of PLLA homo‐crystallization due to stereocomplex (SC) crystallite formation are investigated in PLLA films doped with PDLA over the wide concentration range of 1–10 wt%. PLLA homo‐crystallization is accelerated for all the PDLA concentrations when the processing temperature Tp is just above the endset melting temperature of the SC crystallites (Tp = 226–238 °C), although the appropriate Tp range becomes narrow at low concentrations of PDLA. The accelerating effects of SC crystallites depend on the SC crystalline thickness and the interaction between the SC crystalline regions and PLLA amorphous regions for Tps below and above the melting peak temperature of the SC crystallites, respectively.
This paper reports the properties of highly oriented nanocomposite tapes based on isotactic PP and needle‐like sepiolite nanoclay, obtained by a solid state drawing process. The intrinsic 1D character of sepiolite allows its exploitation in 1D objects, such as oriented polymer fibres and tapes, where it can be uniaxially oriented upon drawing. A synergistic increase in mechanical properties is presented for highly drawn tapes (λ ≤ 20) and low filler loadings (≤2.5 wt.‐%), which can not be simply explained by micromechanical composite models. Instead, mechanical properties are intimately related to the dispersion state of the nanoclays in PP, the rheological properties of the nanocomposites and the polymer morphology.
CNF‐reinforced PP nanocomposites were fabricated from CNFs dispersed in a boiling PP/xylene solution. Their thermal properties were characterized by TGA and DSC and shown to exhibit improved thermal stability and higher crystallinity. They were further processed into thin films by compression molding. The electrical conductivity and dielectric property of the PP/CNF nanocomposite thin films were studied. Both electric conductivity and real permittivity increased with increasing fiber loading. Electrical conductivity percolation is observed between 3.0 and 5.0 wt.‐% fiber loading. The rheological behavior of the nanocomposite melts were also investigated. It was found that a small fiber concentration affects the modulus and viscosity of PP melt significantly.
The effects of process engineering in the fabrication of PHBV, PLA and their blends prepared by melt blending are studied. The elongation of an optimized blend can be improved by 148 and 250% over the virgin PHBV and PLA polymers, respectively. DSC shows that the two polymers are immiscible in blends of any composition. The crystallinity of PHBV is hindered by the presence of PLA. UV‐Vis demonstrates the opacity of the blend with incorporation of PHBV to the PLA phase. The observed tensile modulus of the optimized sample is compared with theoretical values from the rule of mixtures. Gordon‐Taylor's equation is applied on the glass transition temperatures for theoretical modeling to explain the miscibility of the polymers.
A blend composition of poly(3‐hydroxybutyrate‐co‐valerate) and polylactide is used as a bioplastic matrix and reinforced with soy hull to engineer novel green composites. A comparative study with soy‐hull‐reinforced polypropylene composite system is performed. A compatibilizer is used to engineer the novel class of green composites with a balanced stiffness and toughness performance with the target to substitute PP‐based composites. The flexural and impact strength along with hydrophobicity of compatibilized composites are improved significantly over the noncompatibilized counterpart. The fiber/matrix interaction is investigated by SEM. These green composites have the potential to substitute PP‐based composites in some applications.
Cellulose microfibers were modified with two different bi‐functional monomers. Composites of EVA copolymer with modified and unmodified cellulose were prepared by melt mixing. The samples were analyzed by SEM, XRD, FT‐IR, DSC, TGA, DMTA and tensile mechanical tests. SEM showed that the presence of reactive groups on cellulose surface enhanced the compatibility, improving the fiber/matrix interfacial adhesion. FT‐IR disclosed the occurrence of chemical reactions between the functionalized cellulose and polymer chains. The incorporation of fibers affected the crystallization behaviour and crystallinity of the polymer matrix. Composites with GMA modified cellulose displayed better compatibility, higher thermal and mechanical properties.
The long‐term viscoelastic behavior of reinforced all‐poly(propylene) composites was studied by flexural creep tests. Both unidirectional and cross‐ply laminates were prepared from PURE® coextruded tapes by vacuum bag molding in an autoclave. The specimens were subjected to isothermal creep tests at different temperatures ranging from 20 to 80 °C under an applied load. The time‐temperature superposition principle was verified for the creep data. An Arrhenius type relationship was found to better describe the shift data obtained from the creep tests. The activation energies relating to the different reinforcement architecture and different relaxation process were calculated.
Poly(propylene) (PP) composites were prepared by using eggshell (ES) as filler and their mechanical properties were compared with those using talc (TA) and calcium carbonate (CC) of different grain sizes (X50). A decrease in impact strength and deformation at break with increase in filler content was observed. The PP composite with ES (X50 = 8.4 µm) was stiffer than those with CC (X50 = 0.7 µm). The hybrid composite PP‐ES‐TA showed a similar stiffness as the PP‐TA composites due to the similar morphology of TA (X50 = 0.5 µm) and ES, when TA was replaced up to 75 wt.‐% by ES. SEM study revealed evidence of improved interfacial bonding between PP and ES in theirs composites.
Nowadays, silicon represents the most important material used for microelectronic applications. In this paper, both H–Si (111) surfaces and H–Si powders are used to initiate a multifunctional acrylate photopolymerization. The polymers formed are characterized by IR spectroscopy. This should be the way to create either an acrylate polymer coating on a Si wafer or a polymer film containing covalently linked silicon particles.
An in situ lubrication dispersion method is developed to achieve electrical conductivity in PP containing a small amount of MWCNTs. Good dispersion of the MWCNTs in PP is observed even after a short mixing time because the interactions between the entangled nanotubes are reduced. By in situ lubrication dispersion, the electrical percolation threshold of the PP nanocomposite can be as low as 0.5–0.7 wt% MWCNT. Rheological data also support percolation at 0.5 wt% MWCNT. With 0.5 wt% MWCNT, the slope of G′ at low frequency approaches unity and shows non‐terminal behavior. The proposed dispersion method enhances the wetting of MWCNTs and improves MWCNT dispersion compared to both direct mixing of MWCNT powder with a polymer melt and conventional master batch dilution.
Novel nanocomposites based on conductive Ag nanoparticles and a self‐assembled polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) block copolymer were investigated. Good confinement of the nanoparticles into polystyrene microphase was achieved by the addition of DT as surfactant. The polymeric matrix kept its hexagonal order packed cylindrical structure up to 7 wt.‐% content of Ag nanoparticles. An electrostatic force microscopy (EFM) analysis of well‐dispersed metal‐organic hybrid Ag/SBS films was used to characterize the electric behavior of the conductive nanocomposites.
A systematic study of the effects of , flow rate, voltage, and composition on the morphology of electrospun PLGA nanofibers is reported. It is shown that changes of voltage and flow rate do not appreciably affect the morphology. However, the of PLGA predominantly determines the formation of bead structures. Uniform electrospun PLGA nanofibers with controllable diameters can be formed through optimization. Further, multi‐walled carbon nanotubes can be incorporated into the PLGA nanofibers, significantly enhancing their tensile strength and elasticity without compromising the uniform morphology. The variable size, porosity, and composition of the nanofibers are essential for their applications in regenerative medicine.
Blends of PEI with an amorphous copolyester (PCTG) were obtained by melt‐mixing followed by injection molding. The processability of PEI increased several times upon addition of just 10% PCTG, thus expanding the applications of PEI. All the blends showed a single Tg and most of them were transparent. However, they were biphasic as suggested by the widening of the Tg's and proved by SEM. A fine dispersed particle size and good adhesion level were also observed by SEM. The values of the modulus of elasticity and the yield stress appeared close the additivity rule, and were attributed to the combined effects of the density increase and orientation decrease in the blends. These morphological changes had a slightly negative influence on ductility which was nevertheless high.
