The influence of Ca‐stearate‐coated CaCO3 and talc on the quiescent and flow‐induced crystallization of iPP is studied using different methods. Comparison of rheometry and DSC shows that rheometry is an interesting tool to monitor crystallization kinetics. It is observed that the Ca‐stearate coating degrades at commonly used annealing temperatures, influencing the crystallization behavior of the CaCO3‐containing polymer. WAXD indicates that the CaCO3 does not significantly influence the degree of crystallinity. As shear intensifies, both the pure and particle‐containing polymers crystallize faster; however, their behavior also becomes increasingly similar. There are indications that shear influences the organization of the CaCO3 aggregates.
Plastic foams with nano/micro‐scale cellular structures were prepared from poly(propylene)/thermoplastic polystyrene elastomer (PP/TPS) systems, specifically the copolymer blends PP/hydrogenated polystyrene‐block‐polybutadiene‐block‐polystyrene rubber and PP/hydrogenated polystyrene‐block‐polyisoprene‐block‐polystyrene. These PP/TPS systems have the unique characteristic that the elastomer domain can be highly dispersed and oriented in the machine direction by changing the draw‐down ratio in the extrusion process. A temperature‐quench batch physical foaming method was used to foam these two systems with CO2. The cell size and location were highly controlled in the dispersed elastomer domains by exploiting the differences in CO2 solubility, diffusivity, and viscoelasticity between the elastomer domains and the PP matrix. The average cell diameter of the PP/TPS blend foams was controlled to be 200–400 nm on the finest level by manipulating the PP/rubber ratio, the draw‐down ratio of extrusion and the foaming temperature. Furthermore, the cellular structure could be highly oriented in one direction by using the highly‐oriented elastomer domains in the polymer blend morphology as a template for foaming.
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.
2 vol.‐% TiO2 particles were incorporated into PET/PP blends with and without MA‐grafted PP compatibilizer. During extrusion of the PET/PP/TiO2 composites the TiO2 particles migrated from the PP matrix to the PET‐dispersed phase irrespective of the blending route. For the PET/PP/PP‐g‐MA/TiO2 composites, however, the location of TiO2 depended on the blending sequence. The preferred location of the TiO2 nanoparticles was confirmed by SEM pictures taken from the chemically etched surface of the blends. The observed migration behavior was traced to differences in the interfacial tensions between TiO2 and PET and TiO2 and PP, and to TiO2 encapsulation in one of the blend components during the related blending procedure.
Plastic foam with nano‐/micro‐scale cellular structures was prepared from a poly(propylene) (PP)/propylene‐ethylene copolymer (PER) blend by controlling bubble nucleation sites and bubble growth in disperse PER domains. Batch foaming experiments using a CO2 pressure quench method were conducted at room temperature. The bubble size and location were highly controlled in disperse PER domains by exploiting the differences in CO2 solubility and viscoelasticity between the PER domains and the PP matrix. The average cell diameter of PP/PER blend foams can be controlled within 0.5–2 µm by the PP/PER ratio, depressurization rate, and foaming temperature.
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.
Isotactic PP nanocomposites filled with Fe@FeO nanoparticles are fabricated by a facile ex situ method. The nanofillers are dispersed in a boiling PP/xylene solution. X‐ray diffraction is used to determine the nanofiller effects on the crystallinity of PP. The crystallinity along the (040) plane is found to decrease with the incorporation of nanoparticles. Thermal properties and crystallinity are studied by TGA and DSC, respectively. Enhanced thermal stability and influenced crystallinity are observed in the PP nanocomposites compared with those of pure PP. An increased dielectric property without percolation threshold is observed. In addition, the nanocomposites are found to exhibit ferromagnetic properties.
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.
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.
Flexural, impact resistance, tensile, and sound absorption properties of composites from cornhusk fiber (CHF) and PP have been investigated. The effect of holding temperature, CHF length, CHF concentration, and enzyme treatment of CHF on mechanical properties and the effect of the latter two on sound absorption have been studied. Compared with jute/PP composites, CHF/PP composites have similar impact resistance, 33% higher flexural strength, 71% lower flexural modulus, 43% higher tensile strength, 54% lower tensile modulus, and slightly higher noise reduction coefficient. Enzyme treatment of CHF results in increased mechanical and sound absorption properties.
The effect of nanosilica addition on the morphology and mechanical properties of blends of isotactic PP and an ethylene/octene copolymer (EOC) is studied. TEM reveals that the well‐dispersed nanoparticles are localized exclusively in the PP phase. In the presence of a maleated PP compatibilizer addition of nanosilica leads to more finely dispersed EOC domains and a finer co‐continuous morphology. The nanoparticles reduce the rate of coalescence of the dispersed phase domains. The mechanical properties depend on the EOC and PP‐g‐MA content. Tensile and flexural properties are significantly enhanced in the presence of the silica nanoparticles, whereas impact properties are not affected. These enhancements are attributed to the favorable microstructure of the blends.
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.
pCBT/MWCNT nanocomposites were prepared by in situ polymerization of CBT after solid‐phase HEBM of the polymerization catalyst containing CBT with MWCNT. The crystallinity and crystallization behavior of the pCBT nanocomposites were studied by WAXS and DSC. The MWCNTs did not affect the crystallinity of the isothermally produced pCBT significantly, but acted as nucleation agents during the crystallization of pCBT from its melt. pCBT/MWCNT nanocomposites were subjected to DMTA, static flexure, and dynamic Charpy impact tests. The flexural modulus, strength, and impact strength from these tests all went through a maximum as a function of the MWCNT content. Optimum properties were found in the MWCNT range of 0.25–0.5 wt.‐%.
Shape‐memory properties such as shape fixity and recovery ratio of amorphous starch‐based materials extruded under normal conditions were evaluated for the case of single and cyclic recovery processing. This study focused on the effect of moisture as a stimulus for the activation of recovery. A high recovery ratio (Rr > 90%) was obtained at high relative humidity, at deformation ratios up to 200%. In the case of plasticized starch with a glycerol content of 10%, the recovery ratio was close to 50% because crystallization limited the shape recovery. Results were compared to those obtained with synthetic or bio‐based shape‐memory polymers such as semi‐crystalline PU or PLAGC. Efficient shape memory properties for a non‐modified biopolymer are highlighted in this study.
PCL‐based nanoclay (layered silicate) nanocomposites are prepared using a small scale intermeshing co‐rotating twin‐screw extruder. Improving the level of nanoclay dispersion in PCL nanocomposites is obtained by changing the extrusion parameters. Increasing the screw speed and decreasing the throughput leads to an improved dispersion quality, as observed from the improved mechanical properties of the nanocomposites as well as from their clearly affected rheological and crystallization behavior. Furthermore, a commercially available software that simulates the twin‐screw extrusion process (LUDOVIC) is used to asses the processing parameters applied for making the nanocomposites.
Natural rubber (NR) composites containing graphene (GE) are prepared by ultrasound‐assisted latex mixing and in situ reduction. The fatigue crack propagation of the composite is examined. It is observed that GE has an opposite effect on crack growth resistance of NR, i.e., at lower fatigue strains, the inclusion of GE accelerates the crack growth, whereas at higher strains, the crack growth is retarded. It is suggested that the reason for this behavior is a competition between strain‐induced crystallization and cavitation at crack tip. Through microfocus hard‐X‐ray diffraction beamline with high spatial resolution, fatigue crack resistance is correlated to strain‐induced crystallization and new insights into the mechanism of fatigue crack growth are obtained.
Electroactive macroporous poly[(vinylidene fluoride)‐co‐trifluoroethylene] membranes have been produced by solvent evaporation at room temperature, starting with a diluted solution of the copolymer in dimethylformamide. The pore architecture consists of interconnected spherical pores. This architecture is independent of the membrane thickness. The thickness of the membranes ranges from a few to several hundred µm, using spin coating and evaporation in static conditions, respectively. The pore structure is explained by a spinodal decomposition of the liquid/liquid phase separation and crystallization in the copolymer‐rich phase.
TREF fractionation was combined with SEC‐FTIR analysis to measure the compositional heterogeneity within a commercial impact PP copolymer. The chemical composition of all fractions was determined as function of their molecular weight distribution. This approach proved to be highly successful at identifying different constituents within fractions exhibiting bimodal molecular weight distributions. Furthermore, the determination of ethylene and propylene crystallinity distribution across the molecular weight distribution confirmed the morphological nature of each of the components of the bimodal distribution. It is demonstrated that the combination of TREF and SEC‐FTIR provides a simple alternative to more time‐consuming conventional ways of characterising impact PP copolymers of complex heterogeneity.
Chemical modification of EVOH in the molten state at 185 °C by a grafting from process of poly(ε‐caprolactone) in batch was studied. 1H NMR was used to characterize the structure evolutions of PCL grafts. In addition to grafting reactions, dynamic covalent transesterification reactions between EVOH residual alcohols and the polyester grafts led to a redistribution of the PCL grafts length. up to 27 and SR up to 80% were obtained. Experiments made in a corotating mini twin‐screw extruder also confirmed these results. The effect of the alcohol to caprolactone ratio and catalyst concentration (SnOct2) on kinetic evolution showed that few minutes were necessary to complete the polymerization. A kinetic model was proposed and adequate conditions for the synthesis by reactive extrusion were defined.
This work reports a facile route to synthesize homochiral and stereocomplexed polylactide by reactive extrusion. The effect of the polymerization catalyst (combination of tin(II)octanoate and triphenylphosphine) before and after its deactivation is discussed. Poly‐L ‐lactide (PLLA) exhibits homochiral crystallinity and diblock poly‐L ,D ‐lactide (PDLLA) exhibits stereocomplex crystallinity. The presence of residual monomer leads to a plasticizing effect, reducing glass transition temperature (Tg). Changes of the tacticity (L ,D ‐tacticity) of the stereocomplex are due to the transesterification reactions between L and D units. Deactivation of the catalyst reduces transesterification reactions and preserves the polylactide stereocomplex upon heating.
