Morphology, structure, and properties of in situ compatibilized linear low-density polyethylene/polystyrene and linear low-density polyethylene/high-impact polystyrene blends

Blends of linear low-density polyethylene (LLDPE) with polystyrene (PS) and blends of LLDPE with high-impact polystyrene (HIPS) were prepared through a reactive extrusion method. For increased compatibility of the two blending components, a Lewis acid catalyst, aluminum chloride (AlCl3), was adopted to initiate the Friedel-Crafts alkylation reaction between the blending components. Spectra data from Raman spectra of the LLDPE/PS/AlCl3 blends extracted with tetrahydrofuran verified that LLDPE segments were grafted to the para position of the benzene rings of PS, and this confirmed the graft structure of the Friedel-Crafts reaction between the polyolefin and PS. Because the in situ generated LLDPE-g-PS and LLDPE-g-HIPS copolymers acted as compatibilizers in the relative blending systems, the mechanical properties of the LLDPE/PS and LLDPE/HIPS blending systems were greatly improved. For example, after compatibilization, the Izod impact strength of an LLDPE/PS blend (80/20 w/w) was increased from 88.5 to 401.6 J/m, and its elongation at break increased from 370 to 790%. For an LLDPE/HIPS (60/40 w/w) blend, its Charpy impact strength was increased from 284.2 to 495.8 kJ/m(2). Scanning electron microscopy micrographs showed that the size of the domains decreased from 4-5 to less than 1 mum, depending on the content of added AlCl3.

Characterization and properties of the neutral and doped blends of poly(3-dodecylthiophene) with low-density polyethylene

In this paper, the structures and properties of the neutral and doped blends of poly(3-dodecylthiophene) (P3DDT) with low-density polyethylene (LDPE) were investigated. Wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), Fourier transform infrared spectra (FTIR), and scanning electron microscopy (SEM) were used to characterize the structures and morphologies of the blends, and conductivity was also measured. It was found that separate crystallizations occur between P3DDT and LDPE. When the amount of P3DDT is small in the blend, it has the effect of a nucleation reagent and has some influence on the crystal structure. After doping, the interaction force between the molecular chains increases, and leads to a more compact packing and a more uniform dispersion in morphology. Through blending, the thermal stability of pure component could be greatly improved, especially when the P3DDT content is 5 wt %. The conductivity measurements indicate that the conductivity increases with the increase of the P3DDT composition and doping time.

Effect of the compatibilization of linear low-density polyethylene-g-acrylic acid on the morphology and mechanical properties of poly(butylene terephthalate)/linear low-density polyethylene blends

A poly(butylene terephthalate) (PBT)/linear low-density polyethylene (LLDPE) alloy was prepared with a reactive extrusion method, For improved compatibility of the blending system, LLDPE grafted with acrylic acid (LLDPE-g-AA) by radiation was adopted in place of plain LLDPE. The toughness and extensibility of the PBT/LLDPE-g-AA blends, as characterized by the impact strengths and elongations at break, were much improved in comparison with the toughness and extensibility of the PBT/LLDPE blends at the same compositions. However, there was not much difference in their tensile (or flexural) strengths and moduli. Scanning electron microscopy photographs showed that the domains of PBT/LLDPE-g-AA were much smaller and their dispersions were more homogeneous than the domains and dispersions of the PBT/ T,T PE blends. Compared with the related values of the PBT/LLDPE blends, the contents and melting temperatures of the usual spherulites of PBT in PBT/LLDPE-g-AA decreased.

Blends of linear low-density polyethylene and a diblock copolymer of hydrogenated polybutadiene and methyl methacrylate

Blends of linear low-density polyethylene (LLDPE) and a diblock copolymer of hydrogenated polybutadiene and methyl methacrylate [P(HB-b-MMA)] were studied by transimission electron microscope (TEM), differential scanning calorimetry (DSC), and wide angle X-ray diffraction (WAXD). At 10 wt% block copolymer content, block copolymer chains exist as spherical micelles and cylindrical micelles in LLDPE matrix. At 50 wt% block copolymer content, block copolymer chains mainly form cylindrical micelles. The core and corona of micelles consist of PMMA and PHB blocks, respectively. DSC results show that the total enthalpy of crystallization of the blends varies linearly with LLDPE weight percent, indicating no interactions in the crystalline phase. In the blends, no distortion of the unit cell is observed in WAXD tests.

Critical crystallization temperature for the occurrence of epitaxy between high-density polyethylene and isotactic polypropylene

The crystallization behavior of high-density polyethylene (HDPE) on highly oriented isotactic polypropylene (iPP) at elevated temperatures (e.g., from 125 to 128 degrees C), was studied using transmission electron microscopy and electron diffraction. The results show that epitaxial crystallization of HDPE on the highly oriented iPP substrates occurs only in a thin layer which is in direct contact with the iPP substrate, when the HDPE is crystallized from the melt on the oriented iPP substrates at 125 degrees C. The critical layer thickness of the epitaxially crystallized HDPE is not more than 30 nm when the HDPE is isothermally crystallized on the oriented iPP substrates at 125 degrees C. When the crystallization temperature is above 125 degrees C, the HDPE crystallizes in the form of crystalline aggregates and a few individual crystalline lamellae. But both the crystalline aggregates and the individual crystalline lamellae have no epitaxial orientation relationship with the iPP substrate. This means that there exists a critical crystallization temperature for the occurrence of epitaxial crystallization of HDPE on the melt-drawn oriented iPP substrates (i.e., 125 degrees C). (C) 1997 John Wiley & Sons, Inc.

Miscibility of linear low density polyethylene (LLDPE)-graft-poly(methyl methacrylate) with poly(vinylidene fluoride) (PVF2) and its application as compatibilizer LLDPE/PVF2 blends

Differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used to study the miscibility of blends of a graft copolymer of poly(methyl methacrylate) on linear low density polyethylene (LLDPE-g-PMMA, G-3) with poly(vinylidene fluoride)(b) (PVF2) and the compatibilization of blends of LLDPE/PVF2. The specific interaction between PMMA side chains and PVF2 in G-3/PVF2 binary blends is weaker than that between the homopolymers PMMA and PVF2. There are two states of PVF2 in the melt of a G-3/PVF2 (60/40, w/w) blend, one as pure PVF2 and the other interacting with PMMA side chains. The miscibility between PMMA side chains and PVF2 affects the crystallization of PVF2. LLDPE-g-PMMA was demonstrated to be a good compatibilizer in LLDPE/PVF2 blends, improving the interfacial adhesion and dispersion in the latter. Diffusion of PMMA side chains into PVF2 in the interfacial region reduces the crystallization rate and lowers the melting point (T-m) and the crystallization temperature (T-c) of PVF2 in the blends.

SYNTHESIS OF A POLYETHYLENE-GRAFT-POLYSTYRENE COPOLYMER AND ITS COMPATIBILIZATION FOR LINEAR LOW-DENSITY POLYETHYLENE/POLY(PHENYLENE OXIDE) BLENDS

Based on unsteady diffusion kinetics, polyethylene(PE)-graft-polystyrene (PS) copolymers were designed and synthesized with a heterogeneous high yield titanium-based catalyst by copolymerization of ethylene with a PS-macromonomer using 1-hexene as a short chain agent to promote the incorporation of the PS-macromonomer. The presence of 1-hexene facilitated the diffusion of the PS-macromonomer, giving rise to the significantly increased incorporation of the PS-macromonomer. Compatibilization of blends of linear low density polyethylene (LLDPE)/poly(phenylene oxide) (PPO) with the PE-g-PS copolymer were investigated using scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA).

EPITAXIAL CRYSTALLIZATION OF HIGH-DENSITY POLYETHYLENE ON POLYPROPYLENE IN SOLUTION-CAST FILMS

Epitaxial crystallization of high-density polyethylene (HDPE) on isotactic polypropylene (iPP) in solution-cast films has been investigated by electron microscopy. The specimen-tilt technique of electron microscopy has been used to study the structural relationship between HDPE and iPP crystals. HDPE exhibits different crystalline morphologies in the two basic types of iPP spherulite textures, cross-hatched and lathlike regions. In the former, the crystallographic c axis of HDPE lamellae is in the film plane, while in the latter, the c axis of HDPE crystallites is at an angle of about 50-degrees with the normal of the film. In both structural regions of iPP, however, the contact planes of epitaxial growth are (0 1 0) for iPP and (1 0 0) for HDPE.