Structure and oxygen‐barrier properties of (linear low‐density polyethylene/ethylene–vinyl alcohol copolymer)/linear low‐density polyethylene composite films prepared by microlayer coextrusion

Ethylene–vinyl alcohol copolymer (EVOH) and linear low‐density polyethylene (LLDPE) blends with 5% LLDPE grafted with 1% maleic anhydride (MAH; EVOH/LLDPE/LLDPE‐g‐MAH), created to increase the interfacial compatibility, were coextruded with pure LLDPE through the microlayer coextrusion technology. The phase morphology and gas‐barrier properties of the alternating‐layered (EVOH/LLDPE/LLDPE‐g‐MAH)/LLDPE composites were studied by scanning electron microscopy observation and oxygen permeation coefficient measurement. The experimental results show that the EVOH/LLDPE/LLDPE‐g‐MAH and LLDPE layers were parallel to each other, and the continuity of each layer was clearly evident. This structure greatly decreased the oxygen permeability coefficient compared to the pure LLDPE and the barrier percolation threshold because of the existence of the LLDPE/EVOH/LLDPE‐g‐MAH blend layers, and the LLDPE layers diluted the concentration of EVOH in the whole composites. In addition, the effects of the layer thickness ratio of the EVOH/LLDPE/LLDPE‐g‐MAH and LLDPE layers and the layer number on the barrier properties of the layered composites were investigated. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42211.     

Effect of blending high‐pressure low‐density polyethylene on the crystallization kinetics of linear low‐density polyethylene

It is well known that the addition of a small amount of high‐pressure low‐density polyethylene (HP‐LDPE) to linear low‐density polyethylene (LLDPE) can improve the optical properties of LLDPE, and LLDPE/HP‐LDPE blend is widely applied to various uses in the field of film. The optical haziness of polyethylene blown films, as a result of surface irregularities, is thought to be as a consequence of the different crystallization mechanisms. However, not much effort has been directed toward understanding the effect of HP‐LDPE blending on the overall crystallization kinetics (k) of LLDPE including nucleation rate (n) and crystal lateral growth rate (v). In this study, we investigated the effect of blending 20% HP‐LDPE on the crystallization kinetics of LLDPE polymerized by Ziegler‐Natta catalyst with comonomer of 1‐butene. Furthermore, by combining depolarized light intensity measurement (DLIM) and small‐angle laser light scattering (SALLS), we have established a methodology to estimate the lateral growth rate at lower crystallization temperatures, in which direct measurement of lateral growth by polarized optical microscopy (POM) is impossible due to the formation of extremely small spherulites. This investigation revealed that HP‐LDPE blending leads to enhanced nucleation rate, reduced crystal lateral growth rate, and a slight increase in the overall crystallization kinetics of pure LLDPE. From the estimated crystal lateral growth rate, it was found that the suppression in v from HP‐LDPE blending is larger at lower temperatures than at higher temperatures. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Degradation behaviors of linear low‐density polyethylene and poly(L‐lactic acid) blends

In this study, the degradability of linear low‐density polyethylene (LLDPE) and poly(L ‐lactic acid) (PLLA) blend films under controlled composting conditions was investigated according to modified ASTM D 5338 (2003). Differential scanning calorimetry, X‐ray diffraction, and Fourier transform infrared spectroscopy were used to determine the thermal and morphological properties of the plastic films. LLDPE 80 (80 wt % LLDPE and 20 wt % PLLA) degraded faster than grafted low‐density polyethylene–maleic anhydride (M‐g‐L) 80/4 (80 wt % LLDPE, 20 wt % PLLA, and 4 phr compatibilizer) and pure LLDPE (LLDPE 100). The mechanical properties and weight changes were determined after composting. The tensile strength of LLDPE 100, LLDPE 80, and M‐g‐L 80/4 decreased by 20, 54, and 35%, respectively. The films, as a result of degradation, exhibited a decrease in their mass. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Quantitative analysis of cloisite 93A infused into linear low‐density polyethylene and maleated linear low‐density polyethylene in a supercritical carbon dioxide medium

Linear low‐density polyethylene (LLDPE) is a widely used polymer that can benefit from the enhanced barrier, thermal, and mechanical properties offered by nanoclay fillers. However, optimal property enhancement requires complete exfoliation and uniform dispersion, both of which are difficult to achieve with nanoclay fillers. Supercritical carbon dioxide (scCO₂) processing is an inexpensive and environmentally benign method for exfoliating and dispersing clays into polymers. In a scCO₂ medium under controlled environments, the organically modified clay Cloisite 93A was infused into LLDPE and maleated linear low‐density polyethylene (LLDPE‐g‐MA). Upon microscopic inspection, it was evident that clay infusion was achieved near the surface of the polymer pellet, but no clay found its way into the interior of the pellet. In this article, we describe an analytical method for determining the amount of nanoclay infused into a polymer matrix via Fourier transform infrared analysis. Using this method, we determined the weight percentage of Cloisite 93A infused into LLDPE and LLDPE‐g‐MA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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/LLDPE 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. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1059–1066, 2002; DOI 10.1002/app.10399     

Thermal properties and morphology of noncrosslinking linear low‐density polyethylene‐grafted acrylic acid

Noncrosslinking linear low‐density polyethylene‐grafted acrylic acid (LLDPE‐g‐AA) was prepared by melt‐reactive extrusion in our laboratory. The thermal behavior of LLDPE‐g‐AA was investigated by using differential scanning calorimetry (DSC). Compared with neat linear low‐density polyethylene (LLDPE), melting temperature (T_m) of LLDPE‐g‐AA increased a little, the crystallization temperature (T_c) increased about 4°C, and the melting enthalpy (ΔH_m) decreased with an increase in acrylic acid content. Isothermal crystallization kinetics of LLDPE and LLDPE‐g‐AA samples were carried out by using DSC. The overall crystallization rate of LLDPE was smaller than that of grafted samples. It showed that the grafted acrylic acid monomer onto LLDPE acted as a nucleating agent. Crystal morphologies of LLDPE‐g‐AA and LLDPE were examined by using SEM. Spherulite sizes of LLDPE‐g‐AA samples were lower than that of LLDPE. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2626–2630, 2002     

Essential work of fracture evaluation of fracture behavior of glass bead filled linear low‐density polyethylene

The effect of the glass bead (GB) size and bead content on the fracture behavior of GB‐filled linear low‐density polyethylene (LLDPE) composites was evaluated by means of the essential work of fracture (EWF). The results indicated the specific EWF (w_e) is lower for the composites than that of pure LLDPE and the obtained w_e values do not show significant differences for the filled samples with different GB diameters. The non‐EWF or plastic work (βw_p) also decreased with the addition of GBs, indicating that less energy is absorbed during the fracture process for the composites filled with different diameter GBs. For the composites filled with GBs of different contents, the w_e decreased with increasing GB contents and the βw_p that was higher than that of pure LLDPE at relatively low contents also decreased with the content of GBs. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1781–1787, 2006     

Synthesis,characterization, and properties of flexible magnetic nanocomposites of cobalt ferrite–polybenzoxazine–linear low‐density polyethylene

A simple method for the preparation of magnetic nanocomposites consisting of cobalt ferrite (CF; CoFe₂O₄) nanoparticles, polybenzoxazine (PB), linear low‐density polyethylene (LLDPE), and linear low‐density polyethylene‐g‐maleic anhydride (LgM) is described. The composites were prepared by the formation of benzoxazine (BA)–CF nanopowders followed by melt blending with LLDPE and the thermal curing of BA. The composites were characterized by X‐ray diffraction, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, universal testing machine measurement, and vibrating sample magnetometry. The composites consisting of LLDPE, PB, and LgM (47.5L–47.5PB–5LgM) exhibited a higher tensile strength (23.82 MPa) than pure LLDPE and a greater elongation at break (6.11%) than pure PB. The tensile strength of the composites decreased from 19.92 to 18.55 MPa with increasing CF loading (from 14.25 to 33.25 wt %). The saturation magnetization of the composites containing 33.25 wt % CF was 18.28 emu/g, and it decreased with decreasing amount of CF in the composite. The composite films exhibited mechanical flexibility and magnetic properties. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Mechanical properties and morphology of polylactide,linear low‐density polyethylene,and their blends

Melt blending of linear low density polyethylene (LLDPE) and polylactide (PLA) was performed in an extrusion mixer with post extrusion blown film attachment with and without compatibilizer‐grafted low density polyethylene maleic anhydride. The blend compositions were optimized for tensile properties as per ASTM D 882‐91. On the basis of this, LLDPE 80 [80 wt % LLDPE and 20 wt % poly(L ‐lactic acid) (PLLA)] and MA‐g‐low‐density polyethylene 80/4 (80 wt % LLDPE, 20 wt % PLLA, and 4 phr compatibilizer) were found to be an optimum composition. The blends were characterized according to their mechanical, thermal, and morphological behavior. Fourier transform infrared spectroscopy revealed that the presence of compatibilizer enhanced the blend compatibility to some extent. The morphological characteristics of the blends with and without compatibilizer were examined by scanning electron microscopy. The dispersion of PLLA in the LLDPE matrix increased with the addition of compatibilizer. This blend may be used for packaging applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Rheological properties and morphology of compatibilized poly(butylene terephthalate)/linear low‐density polyethylene alloy

The rheological behavior of PBT/LLDPE and PBT/LLDPE‐g‐AA blends [where PBT is poly(butylene terephthalate), LLDPE is linear low‐density polyethylene, and AA is acrylic acid] under a capillary flow was investigated with a capillary rheometer. The Utracki equation was used to describe the viscosity–composition dependence of PBT/LLDPE and PBT/LLDPE‐g‐AA blends at low shear stresses. However, at high shear stresses, this equation was not suitable for these blending systems. There existed a maximum on the curves of the entrance pressure drop versus the blending compositions, and the interlayer slip factor β in the Utracki equation was related not only to the shear stress but also to the elasticity difference of the two blending components. Morphological observations indicated that at high shear rates, there existed two different morphologies at different positions of the extrudates, and this was the reason that the Utracki equation failed. Near the wall of the capillary, low‐viscosity PBT stratified, and this resulted in an additional decrease in the viscosities of the blending systems. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 206–213, 2003     

Synthesis and characterization of linear low‐density polyethylene/sepiolite nanocomposites

Linear low‐density polyethylene (LLDPE)/sepiolite nanocomposites were prepared by melt blending using unmodified and silane‐modified sepiolite. Two methods were used to modify sepiolite: modification before heat mixing (ex situ) and modification during heat mixing (in situ). The X‐ray diffraction results showed that the position of the main peak of sepiolite remained unchanged during modification step. Infrared spectra showed new peaks confirming the development of new bonds in modified sepiolite and nanocomposites. SEM micrographs revealed the presence of sepiolite fibers embedded in polymer matrix. Thermogravimetric analysis showed that nanocomposites exhibited higher onset degradation temperature than LLDPE. In addition, in situ modified sepiolite nanocomposites exhibited higher thermal stability than ex situ modified sepiolite nanocomposites. The ultimate tensile strength and modulus of the nanocomposites were improved; whereas elongation at break was reduced. The higher crystallization temperature of some nanocomposite formulations revealed a heterogeneous nucleation effect of sepiolite. This can be exploited for the shortening of cycle time during processing. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal properties and morphology of recycled poly(ethylene terephthalate)/maleic anhydride grafted linear low‐density polyethylene blends

Properties of recycled Poly(ethylene terephthalate) were greatly improved. Recycled PET was blended with LLDPE‐g‐MA by low‐temperature solid‐state extrusion. Mechanical properties of the blends were affected obviously by the added LLDPE‐g‐MA. Elongation at break reaches 352.8% when the blend contains 10 wt % LLDPE‐g‐MA. Crystallization behavior of PET phase was affected by LLDPE‐g‐MA content. Crystallinity of PET decreased with the increase of LLDPE‐g‐MA content. FTIR testified that maleic anhydride group in LLDPE‐g‐MA reacted with the end hydroxyl groups of PET and PET‐co‐LLDPE‐g‐MA copolymers were in situ synthesized. SEM micrographs display that LLDPE‐g‐MA phase and PET phase are incompatible and the compatibility of the blends can be improved by the forming of PET‐co‐LLDPE‐g‐MA copolymer. LLDPE‐g‐MA content was less, the LLDPE‐g‐MA phase dispersed in PET matrix fine. With the increase of LLDPE‐g‐MA content, the morphology of dispersed LLDPE‐g‐MA phase changed from spherule to cigar bar, then to irregular spherule. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Physicomechanical,optical, barrier,and WAXS studies of filled linear low‐density polyethylene films

Linear low‐density polyethylene (LLDPE) with different fillers such as silica, mica, and soy protein isolate were compounded using a single screw extruder and blown into films by a Konark blow‐film machine. The filled LLDPE films were characterized for physicomechanical and optical properties. Barrier properties such as water vapor transmission rate and oxygen transmission rate of the filled LLDPE films were also reported. Microcrystalline parameters such as crystal size (〈N〉) and lattice distortion (g in %) of the filled LLDPE films were estimated from the wide‐angle X‐ray scattering method using Hosemann's paracrystalline model. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2938–2944, 2003     

Kinetics of thermal degradation of nanometer calcium carbonate/linear low‐density polyethylene nanocomposites

To improve the thermal properties of linear low‐density polyethylene (LLDPE), the CaCO₃/LLDPE nanocomposites were prepared from nanometer calcium carbonate (nano‐CaCO₃) and LLDPE by melt‐blending method. A series of testing methods such as thermogravimetry analysis (TGA), differential thermogravimetry analysis, Kim‐Park method, and Flynn‐Wall‐Ozawa method were used to characterize the thermal property of CaCO₃/LLDPE nanocomposites. The results showed that the CaCO₃/LLDPE nanocomposites have only one‐stage thermal degradation process. The initial thermal degradation temperature T₀ increasing with nano‐CaDO₃ content, and stability of LLDPE change better. The thermal degradation activation energy (E_a) is different for different nano‐CaCO₃ content. When the mass fraction of nano‐CaCO₃ in nanocomposites is up to 10 wt %, the nanocomposite has the highest thermal degradation E_a, which is higher (28 kJ/mol) than pure LLDPE. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal and dielectric properties of the aluminum particle reinforced linear low‐density polyethylene composites

The possibility of obtaining relatively high thermal conductivity and dielectric constant but low dielectric loss polymeric composites by incorporating the core‐shell‐structured aluminum (Al) particles in a linear low‐density polyethylene (LLDPE) by melt mixing and hot pressing was demonstrated in this study. The morphology, thermal and dielectric properties of the composites were characterized using X‐ray diffractions, thermal analysis, scanning electron microscope, and dielectric analyzer. The Al particle decreases the degree of crystallinity and has no appreciable influence on the melting temperature of LLDPE. The thermal conductivity, dielectric constant and loss factor of the composites increase with an increase in Al content at all the frequencies (1 ～ 10⁶ Hz). The thermal conductivity and dielectric constant of the 70 wt% flaky Al particles filled LLDPE are 1.63 W/mK and 50, much higher than those of the spherical Al reinforced one. Moreover, the surface treatment of Al particles with γ‐Aminopropyltriethoxysilane silane coupler improves the thermal conductivity. The dielectric loss factors of the composites still remain at relatively low levels in the measured frequency range. Further, the dielectric permittivity frequency independence in the measured frequency range was observed due to the nanoscale‐Al‐oxide insulating shell of Al. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Green and self-lubricating polyoxymethylene composites filled with low-density polyethylene and rice husk flour

Polyoxymethylene (POM) composites filled with low-density polyethylene (LDPE) and rice husk flour (RHF) were prepared by injection molding. The POM/5 wt % LDPE/7.5 wt % RHF composite exhibited the lowest wear rate, whereas the coefficient of friction remained low, and the POM/5 wt % LDPE/5 wt % RHF composite had the best mechanical properties. X-ray diffraction analysis was carried out, and the worn surfaces were examined with scanning electron microscopy. The results showed that the addition of the filler reduced the crystallinity degree of the POM composites. The main wear mechanism for unfilled POM was adhesion, whereas for the POM composites, wear seemed to occur mainly by fatigue and abrasion. It was experimentally confirmed that the POM composite filled with LDPE and RHF, which is well-performing, low-cost, and environmentally friendly, could be a potential material for tribological applications. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Linear low‐density polyethylene/(soya powder) blends containing polyethylene‐g‐(maleic anhydride) as a compatibilizer

Blends were made from linear low‐density polyethylene (LLDPE) and various amounts of soya powder. The soya powder content was varied from 5 to 20 wt%. Polyethylene‐g‐(maleic anhydride) (PE‐g‐MA) was used as a compatibilizer. Tensile strength and elongation at break (EB) decreased with increasing soya powder content. However, Young's modulus increased with the incorporation of soya powder. The addition of PE‐g‐MA as a compatibilizer increased the tensile strength, EB, and modulus of the blends. The interfacial adhesion between soya powder and LLDPE was improved by the incorporation of PE‐g‐MA, as demonstrated by scanning electron microscopy. Increasing the content of soya powder reduced the crystallinity of the LLDPE phase. The addition of PE‐g‐MA had no significant effect on melting temperature, but the degree of crystallinity of the LLDPE was increased. The thermal stability of the blends was determined by using thermogravimetric analysis. Thermal stability decreased with increasing soya powder loading. However, the addition of PE‐g‐MA slightly increased the thermal stability of LLDPE/(soya powder) blends. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Morphology and rheological properties of compatibilized low‐density polyethylene/linear low‐density polyethylene/thermoplastic starch blends

Morphology and rheological properties of low‐density polyethylene/linear low‐density polyethylene/thermoplastic starch (LDPE/LLDPE/TPS) blends are experimentally investigated and theoretically analyzed using rheological models. Blending of LDPE/LLDPE (70/30 wt/wt) with 5–20 wt % of TPS and 3 wt % of PE‐grafted maleic anhydride (PE‐g‐MA) as a compatibilizer is performed in a twin‐screw extruder. Scanning electron micrographs show a fairly good dispersion of TPS in PE matrices in the presence of PE‐g‐MA. However, as the TPS content increases, the starch particle size increases. X‐ray diffraction patterns exhibit that with increase in TPS content, the intensity of the crystallization peaks slightly decreases and consequently crystal sizes of the blends decrease. The rheological analyses indicate that TPS can increase the elasticity and viscosity of the blends. With increasing the amount of TPS, starch particles interactions intensify and as a result the blend interface become weaker which are confirmed by relaxation time spectra and the prediction results of emulsion Palierne and Gramespacher‐Meissner models. It is demonstrated that there is a better agreement between experimental rheological data and Coran model than the emulsion models. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44719.     

Preparation and characterization of linear low‐density polyethylene/dickite nanocomposites prepared by the direct melt blending of linear low‐density polyethylene with exfoliated dickite

Dickite particles were exfoliated by the thermal decomposition of molecular urea in the interlayer of dickite. The exfoliated dickite (ED) was composed with linear low‐density polyethylene (LLDPE) to prepare a novel LLDPE/dickite nanocomposite (LDN‐5). X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to evaluate the exfoliation effect. FTIR spectra showed that the inner‐surface hydroxyls of dickite decreased because of the sufficient exfoliation of the dickite layers. The 001 diffraction of dickite in the XRD pattern almost disappeared after exfoliation; this indicated the random orientation of dickite platelets. SEM and TEM micrographs confirmed the effective thermal decomposition of the interlamellar molecular urea ED layers, which resulted in smaller particle sizes and better dispersions of dickite in the resulting LLDPE/dickite composite. The microstructure of LDN‐5 showed that most of the dickite platelets were exfoliated and homogeneously dispersed in the LLDPE; this led to increases in the anticorrosion properties and thermal stabilities of LDN‐5. The results of salt‐spray tests illustrated that the corrosion rate of the iron coupon decreased from 23% (LLDPE packing) to 0.4% (LDN‐5 packing). Moreover, the thermal degradation temperature corresponding to a mass loss of 10% increased from 330°C (pure LLDPE) to 379°C (LDN‐5). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Calendered linear low‐density polyethylene consolidated meat and bone meal composites

Bioplastics produced from meat and bone meal (MBM) suffer from rapid and drastic mechanical property deterioration because of their hydrophilic nature. This study investigates mechanical and water stability of composites produced from introduction of a minor component of a synthetic polyethylene as a binder phase to consolidate MBM. The milled and sieved MBM was compounded with 5–60 wt % linear low‐density polyethylene (LLDPE) and formed into composite sheets by calendering, which is an industrially relevant process. Results indicated that a minimum of 15 wt % LLDPE content was required to form a nominally continuous binder phase that allowed for good processability and environment stability of the composites. As expected, the water vapor permeability (WVP) and water absorption characteristics of the composites were intermediate between those of MBM and LLDPE. Sheets containing 15 wt % LLDPE absorbed up to 35 wt % water. Composites tested after being soaked in water showed an initial decrease in TS of about 30% for the first hour but then remained fairly unchanged in the next 72 hours, confirming their moderate environment stability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41145.