In this work, normal blends, microfibrillar blends and composites were prepared from low density polyethylene (LDPE) and poly(ethylene terephthalate) (PET) in 85/15 and 75/25 w/w% ratio in the presence and absence of a compatibilizer polyethylene grafted with maleic anhydride (PE-g-MA). The microfibrillar composites (MFCs) were prepared using extrusion – drawing – isotropization technique. The morphology development of the microfibrillar blends and composites was studied using scanning electron microscopy (SEM). The presence of 5 wt% PE-g-MA compatibilizer affected the continuity of the fibrils differently in 75/25 and 85/15 w/w% microfibrillar blends. In the case of normal blends the addition of compatibiliser reduced the size of the dispersed PET phase. The presence of PET microfibrils improved the tensile properties of the microfibrillar composites. The normal blends exhibited a relatively ductile failure during tensile loading in comparison with the microfibrillar composites. The microfibrillar nature of the dispersed phase was found to improve the stiffness of the composite rather than their impact strength. 相似文献
Microfibrillar composites (MFC) were prepared from the blends of polypropylene (PP) and poly (ethylene
terephthalate) (PET) at a fixed weight ratio of 85/15. The blending of the mixture was carried out in a
single screw extruder, followed by continuous drawing at a stretch (draw) ratio 5. The stretched blends
were converted into MFC by injection moulding. Scanning electron microscopy (SEM) studies showed that the
extruded blends were isotropic, but both phases possessed highly oriented fibrils in the stretched blends,
which were generated insitu during drawing. The PET fibrils were found to be randomly distributed in the
PP matrix after injection moulding. The non isothermal crystallization behaviour of the as extruded blend,
stretched blend and MFC was compared. The analysis of the crystallization temperature and time characteristics
revealed that the PET fibrils in the stretched blend had a greater nucleating effect for the crystallization
of PP than the spherical PET particles in the as extruded blend and short PET fibrils in the MFC. 相似文献
In situ microfibrillar reinforced blend (MRB) based on poly(ethylene terephthalate) (PET) and isotactic polypropylene (iPP) was elaborated by a slit die extrusion, hot stretching, and quenching process. The scanning electronic microscopic images show well-developed PET microfibers in the blends. The on-line small angle X-ray scattering (SAXS) test shows that PET microfibers have high nucleation for iPP crystallization. At the same time, after shear, neat iPP and microfibrillar blend both can faster crystallization rate. Three nucleation origins are proposed in microfibrillar reinforced blends under shear flow field: (a) the classical row nuclei model, (b) fiber nuclei and (c) nuclei induced by fiber assistant alignment. The polarized optical microscopic images indicate that, during the non-isothermal crystallization at a cooling rate of 10 °C/min from 200 °C to room temperature, the neat iPP forms common spherulites, while the diluted microfibrillar blend with 1 wt% of PET has a typical transcrystalline structure. 相似文献
Poly(ethylene terephthalate) and polypropylene are considered, to be incompatible by the usual criteria for polymer blends. Sheath/core filaments of these polymers could not be oriented because of poor adhesion of the base polymers. Melt blends of the two polymers with 30 and 50 weight percent polypropylene produced useful, oriented monofilaments. Tensile and dynamic mechanical properties of these filaments indicate that the structures consist of interlocked microfibrillar domains of the polyester and polyolefim. The glass transition region of poly(ethylene terephthalate) is not affected by admixture with polypropylene. A fine mutual dispersion of the two polymers was possible because the melt viscosities of the ingredients were reasonably well matched under the conditions of mixing. The melt viscosity and elasticity of blends were lower than those of either component as expected if the two polymers are immiscible. Monofilament extrusion and melt flow measurements were made with a one-half inch single screw extruder. 相似文献
The influence of a complex filler system on the electrical properties of a microfibrillar conductive polymer composite (MCPC) is discussed. By adding insulating filler, nano-CaCO3, to carbon black (CB)-filled MCPC, the morphology of the poly(ethylene terephthalate) (PET) microfibrillar phase was tailored according to the ratio of CB/nano-CaCO3, and so were the electrical properties of MCPC. It was found that nano-CaCO3 did not influence electrical properties in a monotone way. With an increase in nano-CaCO3 content, on one hand, the surface of the microfibrils became smoother, which jeopardized the conductivity of the MCPC. At the same time, the nano-CaCO3 particles substituted for the CB particles on the surface of the microfibrils and further decreased conductivity. On the other hand, longer and better-defined microfibrils could form, which enhanced the conductive network and increased the conductivity of the MCPC. As a result, the percolation threshold changed little compared to the common CB-filled MCPC. 相似文献
The poly(ethylene terephthalate) (PET)/isotactic polypropylene (iPP) in situ microfibrillar blends have been prepared through a “slit die extrusion-hot stretch-quenching” process, in which PET assumes microfibrils with 0.5-15 μm in diameter depending on the hot stretching ratios (HSR, the area of the transverse section of the die to the area of the transverse section of the extrudate). The injection molded specimens of virgin iPP and the PET/iPP blends were prepared by conventional injection molding (CIM) and by shear controlled orientation injection molding (SCORIM), respectively. The effect of shear stress and PET phase with different shape on superstructures and their distribution of injection molded microfibrillar samples were investigated by means of small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS). The shear (or elongational) flow during CIM and SCORIM can induce oriented lamellae (i.e. kebabs induced by shish). The shish-kebab structure appears not only in the skin and intermediated layers of CIM samples, but also in the whole region of SCORIM samples. For the neat iPP samples, a more “stretched” shish-kebab structure with higher orientation degree can be obtained in the interior region (intermediate and core layers) by the SCORIM method; moreover, the SCORIM can result in the growth of β-form crystal both in intermediate layer and in core layer, which only appears in intermediate layer of the neat iPP samples obtained by CIM. For the PET/iPP blends, interestingly, the addition of microfibrils as well as their aspect ratios can affect the orientation degree of kebabs only in the intermediate layers, and the addition of microfibrils with a low aspect ratio can bring out a considerable increase in the orientation degree of kebabs along the flow direction. However, for the SCORIM, the addition of microfibrils seems to be a minor effect on the orientation degree of kebabs, and it tends to hamper the formation of a more “stretched” shish-kebab structure and suppresses the growth of β-form crystal distinctly. Furthermore, It appears from experiment that γ-form crystals can grow successfully in this oriented iPP melt with the synergistic effect of shear and pressure only when the growth of β crystals can be restrained by some factors, such as the PET dispersed phase and thermal conditions (cooling rate). 相似文献
Sheet composites of polypropylene and poly(ethylene terephthalate) were produced by melt consolidation of alternating layers of polymer films and random glass fiber mats. The composites had a nominal glass content of 50 wt% (~30 vol%). The sheets were stamped into a complex part from which test specimens were machined, and mechanical properties determined. Flexural strengths as high as 159 MPa were recorded for polypropylene composites and 313 MPa for poly(ethylene terephthalate) composites. The flexural modulus of the polypropylene composites reached 9.1 MPa, whereas the modulus of the stiffest poly(ethylene terephthalate) composite was 15 GPa. The impact properties of the composites were equally high. Polypropylene composites absorbed up to 257 J/cm during an instrumented falling dart impact test. Poly(ethylene terephthalate) composites absorbed as much as 116 J/cm in the same test. 相似文献
The present article reports the nonisothermal crystallization process and morphological evolution of oriented iPP melt with and without in situ poly(ethylene terephthalate) (PET) microfibrils. The bars of neat iPP and PET/iPP microfibrillar blend were fabricated by shear controlled orientation injection molding (SCORIM), which exhibit the oriented crystalline structure (shish-kebab), especially in the skin layer. The skin layer was annealed at just above its melting temperature (175 °C) for a relatively short duration (5 min) to preserve a certain level of oriented iPP molecules. It was found that the existence of ordered clusters (i.e. oriented iPP molecular aggregates) leads to the primary nucleation at higher onset crystallization temperature, and formation of the fibril-like crystalline morphology. However, the overall crystallization rate decreases as a result that the relatively high crystallization temperature restrains the secondary nucleation. With the existence of PET microfibrils, the heterogeneous nucleation distinctly occurs in the unoriented iPP melt and results in the increase of crystallization peak temperature and overall crystallization rate, for the first time, we observed that the onset crystallization temperature has been enhanced further with addition of PET microfibrils in the oriented iPP melt, indicating the synergistic effect of row nucleation and heterogeneous nucleation under quiescent condition. 相似文献
Repetitive processing was employed to assess the recyclability of in situ microfibrillar poly(ethylene terephthalate) (PET)/high‐density polyethylene (HDPE) blends which were fabricated through a “rectangular slit die extrusion–hot stretching–quenching” process. For comparison, the conventional PET/HDPE blends were also obtained using the same processing operation but without hot stretching. The morphological observation indicated that slit die extrusion and hot stretching successfully made the dispersed PET phase deform in situ into well‐defined microfibrils. The average diameter of the microfibrils increased with the processing cycles. The rheological properties obtained from the parallel‐plate dynamic rheometer suggested that the microfibrillar blends have higher viscosity and viscoelastic moduli (storage and loss moduli) as well as better flow stability than the conventional PET/HDPE blend. More importantly, with the increase in the processing cycles, an increase in yield strength and unchanged tensile modulus were observed for in situ microfibrillar blends, while a decrease in these properties for conventional blend, indicating that the in situ microfibrillar PET/HDPE blends have promising recycling potential.