THERMAL BEHAVIOR OF THERMOTROPIC HYDROXYETHYL CELLULOSE ACETATE/POLYETHYLENE BLENDS

The thermal behavior of thermotropic hydroxyethyl cellulose acetate (HECA)/polyethylene (PE) blends has been studied by DSC. It is found that the blends of HECA and PE are immiscible but the crystallization of PE is affected by HECA chains in the blends with more than 50% HECA, which results in the subordinate crystallization of PE and the formation of imperfect structures in the PE crystals. The imperfection of PE crystals in the blends can be eliminated after annealing at 393K.

TIME-DEPENDENT MORPHOLOGY OF POLYETHYLENE-POLYPROPYLENE BLENDS

The effect of time-temperature treatment on morphology of polyethylene-polypropylene (PE-PP) blends wasstudied to establish a relationship between thermal history, morphology and mechanical properties. Polypropylene (PP)homopolymers were used to blend with various polyethylenes (PE), including high density polyethylene (HDPE), lowdensity polyethylene (LDPE), linear low density polyethylene (LLDPE), and very and ultra low density polyethylene(VLDPE and ULDPE). The majority of the blends were prepared at a ratio of PE:PP = 80:20, while blends of PP and LLDPEwere prepared at various compositions. Thermal treatment was carried out at temperatures between the crystallizationtemperatures of PP and PEs to allow PP to crystallize first from the blends. On cooling further, PE crystallized too. A verydiffuse PP spherulite morphology in the PE matrix was formed in some partially miscible blends when PP was less than 20%by mass. Droplet-matrix structures were developed in other blends with either PP or PE as dispersed domains in a continuousmatrix, depending on the composition ratio. The scanning electron microscopy (SEM) images displayed a fibrillar structureof PP spherulite in the LLDPE-PP (80:20) and large droplets of PP in the HDPE-PP (80:20) blend, providing larger surfacearea and better bonding in the LLDPE-PP (80:20) blends. This explains why the blends with diffuse spherulite morphologyshowed greater improvement in tensile properties than droplet-matrix morphology blends after time-temperature treatment.

Effect of Components on the Performance of Asphalt Modified by Waste Packaging Polyethylene

Waste packaging polyethylene（WPE） was used to modify raw asphalt by melt blending the components at 190 ℃ for 1 h in a simple mixer and subsequently machining them at 120 ℃ for 1 h in a highspeed shearing machine.The effect of modification on the degree of the penetration,the softening point and the ductility of the asphalt was studied using fluorescent microscopy,infrared spectrometry,component changes and various other techniques.The experimental results showed that no chemical reactions took place in the components themselves（saturate,aromatic,asphaltene and resin） during the modifications.The softening point and penetration of the asphalt were found to be closely related to the resulting contents of the asphaltene,saturate and resin components.In addition,aromatics were identified as having the greatest impact on the ductility of the asphalt.

Morphology and Mechanical Properties of Immiscible Polyethylene/Polyamide12 Blends Prepared by High Shear Processing

In this work, completely immiscible polyethylene/polyamidel2 （PE/PA12） blends were prepared by high shear extruder. The morphology and mechanical properties of the blends were investigated as a function of rotation speed. It was found that the high shear processing is an effective method to improve the dispersion of the PAl2 phase in PE matrix when PA 12 contents are 5 wt% and 10 wt%, and the dispersed phase particle size is reduced with the increase of rotation speed from 100 r/min to 500 r/min. However, with further increase of PAl2 content to 20 wt%, high shear processing has no effect on the phase morphology of the blends. Accordingly, a largely increased elongation at break and impact strength are observed for PE/PAl2/95/5 and PE/PA12/90/10 blends obtained at high rotation speeds but no effect on the property of PE/PAI2/80/20. Annealing experiment demonstrated that the obtained phase morphology is not stable thus compatibilizer should be introduced in the future work. This work could provide a guideline for the application of high shear processing in the preparation of polymer blends with huge polarity difference.

Uniform to Accelerated Crystal Twisting Transition in Deuterate Polyethylene/Poly(ethylene-alt-propylene) Blend Films

A uniform to accelerated crystal twisting transition is observed in deuterate polyethylene/poly（ethylene-alt- propylene） （d-PE/PEP） blend films. And the band period is a function of initial d-PE concentration, quench depth and annealing time of phase separation. As Keith and Padden suggested, twisting of lamella is due to the unbalanced stress on its both sides, which can supply a satisfying explanation to banded spherulites formed in homogeneous systems. When it comes to d-PE/PEP blend system, in homogeneous 99% d-PE/PEP （weight fraction of d-PE） blend film, the formation of banded spherulite is observed as a result of uniform twisting of ribbon like d-PE lamellae along the radial direction. With the amorphous PEP piling up, it transfers into accelerated edge-on to fiat-on twisting due to crystallization assisted phase separation. The mechanism can be interpreted as following： d-PE molecules must inter-diffuse to the twisting growth front to continue the secondary nucleation and growth process. Meanwhile, the amorphous PEP molecules are rejected and accumulated at the twisting growth front. Once the d-PE lamella begins to twist because of unbalanced stress on both sides, the accumulated rubber phase at the growth front strengthens the unbalance and accelerates the edge-on to flat-on twisting. The concentration wave propagates further away with constant speed, and leads to concentric ring pattern with periodic nonuniform twisting along the radial direction. Since this is a kinetic effect, the band period can be controlled through initial d-PE concentration, quench depth and annealing time of phase separation. Our result shows that crystallization assisted phase separation can modify lamella growth kinetic pathway, thereby assisting concentric ring pattern formation.

Thermomechanical and Shape Memory Properties of SCF/SBS/LLDPE Composites

A thermally triggered shape memory polymer composite was prepared by blending short carbon fiber（SCF） into a blend of poly（styrene-b-butadiene-b-styrene） triblock copolymer（SBS）/linear low density polyethylene（LLDPE） prior to curing. These composites have excellent processability compared with other thermosets. The dynamic mechanical analysis（DMA） and differential scanning calorimetry（DSC） were investigated to assess the thermomechanical properties of the SCF/SBS/LLDPE composite. Scanning electron microscope（SEM） imaging of the samples was performed to show the distribution of the SCF in the composite. The study specifically focused on the effect of SCF on the shape memory behavior of the SCF/SBS/LLDPE composite. The results indicated that the large amount of SCF significantly improved the mechanical property of the polymer composites while not damaging the shape memory performance. The SCF/SBS/LLDPE composites exhibited excellent shape memory behavior when the SCF content was less than 15.0 wt%. Moreover, the shape fixity ratio and shape recovery time of the SCF/SBS/LLDPE composites increased with the SCF content.