Physical properties of polyethylene/silicate nanocomposite blown films

Maleated polyethylene/silicate nanocomposite and maleated polyethylene/SiO₂ blown films were prepared by melt extrusion. The silicate and SiO₂ significantly affected the physical properties of the films. The former films showed higher tensile strength than the latter films. This high reinforcement effect seemed to be attributable to the strong interaction between the matrix and silicate as well as the uniform dispersion of silicate layers in the polymer matrix. The addition of silicate beyond a certain content gave a worse Elmendorf tear strength than SiO₂. The silicate did not increase the falling dart impact strength at all. The worst Elmendorf strength apparently originated from the orientation of anisotropic silicate rather than the orientation of lamellae of the polymer matrix, and the silicate made the films more brittle. The well‐dispersed silicate layers in the polymer matrix gave almost the same optical properties as the pure polymer despite the increase in the silicate content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2131–2136, 2003     

Structure and properties of composites of polyethylene or maleated polyethylene and cellulose or cellulose esters

Composites of linear low‐density poly(ethylene‐co‐butene) (PE) or maleated linear low‐density poly (ethylene‐co‐butene) (M‐PE) and cellulose (CEL), cellulose acetate (CA), cellulose acetate propionate (CAP), or cellulose acetate butyrate (CAB) were prepared in an internal laboratory mixer with 20 wt % polysaccharide. The structure and properties of the composites were studied with tensile testing, dynamic mechanical thermal analysis, differential scanning calorimetry, extraction with a selective solvent, Raman spectroscopy, and X‐ray diffraction. Composites prepared with M‐PE presented yield stress and elongation values higher than those of composites prepared with PE, showing the compatibilizer effect of maleic anhydride. Dynamic mechanical thermal analysis performed for M‐PE–CEL, M‐PE–CA, M‐PE–CAP, and M‐PE–CAB composites showed one glass‐transition temperature (T_g) close to that observed for pure M‐PE, and for M‐PE–CAP, another T_g lower than that measured for the polysaccharide was observed, indicating partial mutual solubility. These findings were confirmed by the extraction of one phase with a selective solvent, gravimetry, and Raman spectroscopy. X‐ray diffraction showed that the addition of CEL, CA, CAP, or CAB had no influence on the lattice constants of PE or M‐PE, but the introduction of the reinforcing material increased the amorphous region. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:402–411, 2007     

Structure and Morphology Development in Films of mLLDPE/LDPE Blends During Blowing

Summary: In this work the analysis of the structure orientation, morphology, relaxation time and optical properties of blown films of mLLDPE, LDPE and their blends were performed by using WAXD, SALS, AFM, DSC and rheological and haze tests. For mLLDPE film, the crystals do not present “a”‐axis orientation along the machine direction; a distinct spherulite like superstructure is seen. The film surface is very rough. The values of bulk and surface haze are higher than LDPE and blends, whereas the relaxation time is lower. For LDPE film the (110) planes are parallel and at same time twisted with respect to the layer of the film with the “a”‐axis well oriented along the machine direction. No spherulite superstructure is observed and the surface of the film is more regular. High values of relaxation time are observed. The surface haze is the predominant contribution to the total haze. For the blend films no clear and distinct spherulite structures are observed. The orientation degree increases with composition never approaching that of LDPE. The surface is very more regular and smooth than that of the pure polymers. The haze values are below the values of pure materials. It was underlined that bulk and surface morphology and orientation degree of the crystalline planes along the machine direction dictate the optical properties of the films. Moreover both orientation and morphology are defined by the PE molecular and melt rheology characteristics, processing conditions and blend composition.

Total, bulk and surface haze of mLLDPE/LDPE blend films as a function of composition.     

Mechanical and antibacterial properties of modified nano‐ZnO/high‐density polyethylene composite films with a low doped content of nano‐ZnO

Nano‐ZnO/high‐density polyethylene (HDPE) composite films were prepared via melt blending and a hot compression‐molding process. The properties, including ultraviolet absorption, mechanical and antibacterial properties of the films, and plasticizing behavior of the composites, were investigated. The results show that the absorbance in the ultraviolet region of the HDPE films was enhanced after the addition of modified nano‐ZnO to the HDPE matrix. Also, we found that improvement in the HDPE films of the tensile strength and elongation at break was achieved by the incorporation of modified ZnO nanoparticles up to 0.5 wt % in contrast with the original nano‐ZnO/HDPE composite films. Antibacterial testing was carried out via plate counting, and the results indicate that the HDPE films doped with modified ZnO nanoparticles showed favorable antibacterial activity, especially for Staphylococcus aureus. However, the low doped content of modified nano‐ZnO in the HDPE matrix made the balance torque of the composites increase slightly. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Uptake of aromatic solvents by polyethylene films

The sorption properties of the solvents benzene, toluene, and xylene in polyethylene films at 40, 60, and 80°C were investigated. The diffusion coefficient increased with an increase in the sorption temperature for the solvents and was highest for xylene and least for benzene. The inability of xylene to show a definite order of the diffusion coefficients at the investigated temperatures was attributed to the presence of two methyl side groups in the molecule. The solubilities of the solvents in polyethylene increased with an increase in the sorption temperature, and the following order of the solubilities could be observed: xylene > toluene > benzene. The permeabilities of the solvents in polyethylene depended on the sorption temperature, and the following order of the permeabilities was observed: xylene > toluene > benzene. The calculated activation energies of sorption in polyethylene films were all positive; benzene had the highest energy of sorption, and xylene had the lowest. The calculated enthalpies of sorption (ΔH_S) were also positive for the three solvents and were in the following order: xylene > toluene > benzene. The calculated entropies of sorption (ΔS) were negative for the solvents and showed trends similar to the variation of ΔH_S among the solvents. The change in the Gibbs free energies of sorption (ΔG_S), evaluated with the expression ΔG_S = ΔH_S ? TΔS (where T is the Kelvin temperature), were all positive, and this was an indication of the nonspontaneity of the solubility of polyethylene in the aromatic solvents at 313 K. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3849–3854, 2007     

Melt strength of linear low‐density polyethylene/low‐density polyethylene blends

Linear low‐density polyethylenes and low‐density polyethylenes of various compositions were melt‐blended with a batch mixer. The blends were characterized by their melt strengths and other rheological properties. A simple method for measuring melt strength is presented. The melt strength of a blend may vary according to the additive rule or deviate from the additive rule by showing a synergistic or antagonistic effect. This article reports our investigation of the parameters controlling variations of the melt strength of a blend. The reciprocal of the melt strength of a blend correlates well with the reciprocal of the zero‐shear viscosity and the reciprocal of the relaxation time of the melt. An empirical equation relating the maximum increment (or decrement) of the melt strength to the melt indices of the blend components is proposed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1408–1418, 2002     

Rheological and thermal properties of single‐site polyethylene blends

Branched polyethylenes, low‐density polyethylenes (LDPE1 and LDPE2) or long‐chain‐branched very low density polyethylenes (VLDPE2), were blended with very low density polyethylenes containing short branches (VLDPE1 and VLDPE3). The rheological and thermal measurements of the pure copolymers and their blends (VLDPE1–LDPE1, VLDPE1–LDPE2, VLDPE1–VLDPE2, and VLDPE2–VLDPE3) were taken by controlled stress rheometry and differential scanning calorimetry, respectively. The shear‐thinning effect became stronger with increasing long‐chain‐branched polymer compositions when it was correlated with the flow behavior index, and the extent of shear thinning was different for each blend set. Stronger shear thinning and a linear composition dependence of the zero‐shear viscosity were observed for the VLDPE1–LDPE1 and VLDPE1–LDPE2 blends. These blends followed the log additivity rule, and this indicated that they were miscible in the melt at all compositions. In contrast, a deviation from the log additivity rule was observed for the VLDPE1–VLDPE2 blend compositions with 50% or less VLDPE2 and for the VLDPE3–VLDPE2 blends with 50% or more VLDPE2. The thermal properties of the blends were consistent with the rheological properties. VLDPE1–LDPE1 and VLDPE1–LDPE2 showed that these blends were characteristic of a single‐component system at all compositions, whereas the phase separation (immiscibility) was detected only for VLDPE1–VLDPE2 blends with 50% or less VLDPE2 and for VLDPE3–VLDPE2 blends with 50% or more VLDPE2. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1549–1557, 2005     

A comprehensive investigation of the origins of surface roughness and haze in polyethylene blown films

In an earlier publication we showed that the optical haze properties of blown and cast polyethylene (PE) films were adversely affected (i.e., haze increased) as a result of enhanced surface roughness caused by the formation of distinct optically anisotropic “spherulitic‐like” superstructures. In this report we have found that for a very wide variety of PE blown films, the total haze percent exhibited a complex parabolic relationship with the logarithm of the recoverable shear strain parameter, γ_∞. At low values of γ_∞, superstructures were developed (as discussed in our previous report) that increased surface roughness and hence total haze. As γ_∞ increased, such superstructures were either significantly diminished in size or altogether absent, giving rise instead to an oriented, row‐nucleated, stacked lamella texture that decreased surface roughness and hence total haze. However, at even higher γ_∞ values, representing highly melt elastic behavior, fine‐scale surface roughness due to high melt elastic instabilities was induced, thereby increasing surface roughness and consequently total haze as well. It was demonstrated in this work that two PE resins could exhibit the same level of total haze as a consequence of two completely different mechanisms or origins. Furthermore, we believe that this is the first time that both very low and very high melt elasticity have been shown as primary causative factors in yielding high haze in PE blown films, albeit for fundamentally very different reasons. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2396–2411, 2002     

Improvement in processability of metallocene polyethylene by ultrasound and binary processing aid

The effect of ultrasonic vibration and binary processing aid in improving the processability of metallocene linear low‐density polyethylene (mLLDPE) was investigated. During extrusion, ultrasonic vibration clearly reduced the die pressure and apparent viscosity of mLLDPE but had only a slight effect on its melt fracture. The effect of diatomite/PEG binary processing aid (BPA) was excellent in reducing the viscosity and eliminating the sharkskin fracture of mLLDPE. The effect of ultrasonic vibration and binary processing aid in improving the processability of mLLDPE was synergetic. With a combination of ultrasonic vibration and a small amount of processing aid, the flowability of mLLDPE was further improved, and the critical shear rate for the onset of sharkskin fracture was increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1927–1935, 2007     

Effect of diatomite/polyethylene glycol binary processing aids on the rheology of a metallocene linear low‐density polyethylene

Flow performance of metallocene linear low‐density polyethylene (mLLDPE) containing small amounts of polyethylene glycol (PEG) diatomite and diatomite/PEG binary processing aids respectively was investigated. The mLLDPE melt viscosity is increased by the addition of diatomite, but is decreased by addition of PEG or the diatomite/PEG binary processing aids. It was also found that the viscosity reduction of mLLDPE with the addition of diatomite/PEG binary processing aid was significantly greater than that obtained with the addition of only PEG. The flow curves of mLLDPE containing diatomite/PEG binary processing aid show extremely lower value and stronger dependence on shear rate than the others. It is suggested that the rheological improvement of mLLDPE with diatomite/PEG binary processing aids resulted not entirely from the wall slip promoted by PEG; the intrinsic structure may have changed under the application of shear flow. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1546–1552, 2004     

Use of purified and modified bentonites in linear low‐density polyethylene/organoclay/compatibilizer nanocomposites

Polyethylene‐based ternary nanocomposites were prepared with different clay structures, obtained by the modification of purified Resadiye bentonite as the reinforcement, a random terpolymer of ethylene, butyl acrylate, and maleic anhydride with the trade name Lotader3210 as the compatibilizer, and linear low‐density polyethylene (LLDPE) as the polymer matrix in an intensive batch mixer. The quaternary ammonium/phosphonium salts used for the modification of bentonite were dimethyldioctadecyl ammonium (DMDA) chloride (Cl), tetrakisdecyl ammonium (TKA) bromide (Br), and tributylhexadecyl phosphonium (TBHP) Br. The effects of the physical properties and structure of the organoclay on the clay dispersion were studied at different clay contents (2 and 5 wt %) and at a compatibilizer/organoclay ratio of 2.5. The extent of organoclay dispersion was determined by X‐ray diffraction (XRD) and was verified by transmission electron microscopy (TEM), mechanical testing, and rheological analysis. XRD analysis showed that the nanocomposite with the organoclay DMDA contained intercalated silicate layers, as also verified by TEM. The TEM analysis of the nanocomposites with TBHP exhibited intercalated/partially exfoliated clay dispersion. TKA, with a crowded alkyl environment, sheltered and hindered the intercalation of polymer chains through the silicate layers. In comparison to pure LLDPE, nanocomposites with a 33–41% higher Young's modulus, 16–9% higher tensile strength, and 75–144% higher elongation at break were produced with DMDA and TBHP, respectively (at 5 wt % organoclay). The storage modulus increased by 807–1393%, and the dynamic viscosity increased by 196–339% with respect to pure LLDPE at low frequencies for the samples with DMDA and TBHP (at 5 wt % organoclay). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

High‐density polyethylene foams. I. Polymer and foam characterization

The density and morphology of closed‐cell high‐density foams were investigated with four different molecular weights of high‐density polyethylene (HDPE). The characterization of polyethylene via rheological methods was used to determine its influence on foam density and morphology. We found that foaming grade decreased with increasing molecular weight and increased with blowing agent content. The average cell size was also a strong function of molecular weight and blowing agent content. Increasing both the molecular weight and amount of blowing agent decreased the cell size. Cell size also increased for our lowest molecular weight HDPE but decreased for the others. Cell density also increased with increasing HDPE molecular weight. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2111–2119, 2003     

The effects of clay dispersion on the mechanical,physical, and flame‐retarding properties of wood fiber/polyethylene/clay nanocomposites

In this study, nanosized clay particles were introduced into wood fiber/plastic composites (WPCs) to improve their mechanical properties and flame retardancy, which are especially important in various automotive and construction applications. A high degree of exfoliation for nanoclay in the wood fiber/high density polyethylene (HDPE) composites was successfully achieved with the aid of maleated HDPE (PE‐g‐MAn), through a melt blending masterbatch process. The structures and morphologies of the composites were determined using X‐ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. This article presents the effects of clay content and degree of clay dispersion on the mechanical and physical properties and flame retardancy of wood fiber/HDPE composites that contained a small amount of clay, in the range of 3–5 wt %. We concluded that achieving a higher degree of dispersion for the nanosized clay particles is critical to enhance the mechanical properties and the flame retardancy of WPCs when small amounts of clay are used. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The role of polymerizable organophilic clay during preparing polyethylene nanocomposite via filling polymerization

Effect of polymerizable montmorillonites (P‐MMTs) on the morphology of polyethylene/montmorillonites (PE/MMTs) nanocomposites during filling polymerization was studied. The microstructure analysis showed that the P‐MMTs were more exfoliatable than nonpolymerizable MMTs in the preparation of PE/MMTs nanocomposites. By examining the influence of the polymerization condition on the microstructure of the resultant nanocomposites, it was confirmed that the shear force formed by the mechanical stirring was the driving force of the exfoliation dispersion of MMT sheets during the filling polymerization. Comparatively, the shear force on MMT sheets might be increased due to strong interaction between PE chains linked to the surface of P‐MMTs and the solvents molecules, which is the reason that polymerizable clay is more exfoliatable than nonpolymerizable clay. The copolymerization between polymerizable modifier and ethylene was confirmed by NMR measurements. Furthermore, the morphology of the resultant nanocomposites was influenced by the concentration of the dispersed P‐MMTs. The degree of exfoliation of the resultant nanocomposites at a relatively low concentration was higher than that at a high concentration. This is because of the multiscale organization of the organoclay dispersed in the organic medium. High exfoliation degree of MMTs and improved interaction between PE matrix and P‐MMTs in PE/P‐MMTs nanocomposites led to significant improvements in mechanical properties and barrier properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Moisture‐sorption characteristics of starch/low‐density polyethylene films

Moisture‐sorption characteristics of starch/low‐density polyethylene (LDPE) blends were carried out at 27°C for water activity (a_w) from 0.1 to 0.9. The sorption data were used to fit six different sorption isotherm models proposed in the literature. The model constants were determined by linear fitting of the sorption equations. The ranges of applicability of water activity for the isotherm models reported in the article lies between 0.1 and 0.4 (monomolecular layer) for the BET model and between 0.3 and 0.9 (multimolecular and capillary condensation layers) for other models. The value of the coefficient of determination (R² = 0.97 ± 0.02) confirms the linear fitting of the equations studied. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1193–1202, 2002; DOI 10.1002/app.10417     

Rheological analysis of vapor‐grown carbon nanofiber‐reinforced polyethylene composites

The melt rheological analysis of high‐density polyethylene reinforced with vapor‐grown carbon nanofibers (VGCNFs) was performed on an oscillatory rheometer. The influence of frequency, temperature, and nanofiber concentration (up to 30 wt %) on the rheological properties of composites was investigated. Specifically, the viscosity increase is accompanied by an increase in the elastic melt properties, represented by the storage modulus G′, which is much higher than the increase in the loss modulus G″. The composites and pure PE exhibit a typical shear thinning behavior as complex viscosity decreases rapidly with the increase of shearing frequency. The shear thinning behavior is much more pronounced for the composites with high fiber concentration. The rheological threshold value for this system was found to be around 10 wt % of VGCNF. The damping factor was reduced significantly by the inclusion of nanofibers into the matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 155–162, 2004     

Examination of the role of oxygen in the photografting of methacrylic acid on a polyethylene film with a mixed solvent consisting of water and organic solvents

The photografting of methacrylic acid (MAA) on a linear low‐density polyethylene film (thickness = 30 μm) under air and nitrogen atmospheres was investigated at 60°C in mixed solvents consisting of water and an organic solvent, with xanthone as a photoinitiator. The organic solvents used were acetone, methanol, tetrahydrofuran, and dioxane. A maximum percentage of grafting occurred at a certain concentration of the organic solvent in the mixed solvent. This was observed for the systems under both air and nitrogen. The grafting reaction under air exhibited an induction period, but the rate of grafting after the period was greater than that under nitrogen. The formation of poly(ethylene peroxide)s by photoirradiation seemed to be a factor for the accelerated photografting under air. On the basis of attenuated total reflection infrared spectroscopy and scanning electron microscopy of the grafted film, the MAA‐grafted chains of the sample prepared under air tended to penetrate more deeply inside the film than those of the sample prepared under nitrogen. The resulting grafted films exhibited a pH‐responsive character: the grafted films shrank in an acidic medium but swelled in alkaline medium. This was evaluated from measurements of dimensional changes in the grafted films. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 992–998, 2003     

Structure and properties of ultraviolet‐irradiated high density polyethylene at different environmental temperatures

C? O, C?O, and C(?O)O oxygen‐containing groups were introduced onto the molecular chain of high‐density polyethylene (HDPE) through ultraviolet irradiation in air. The introduction rate of the oxygen‐containing groups onto HDPE increased with increasing environmental temperature. After ultraviolet irradiation, the molecular weight of HDPE decreased, and its distribution became wider; the melting temperature, contact angle with water, and impact strength decreased; the degree of crystallinity and yield strength increased; and their variation amplitude increased with environmental temperature. The environmental temperature had an effect on the gel content of irradiated HDPE. HDPE‐irradiated for 48 h at 35° and 50°C were not crosslinked. However, gelation took place in HDPE irradiated for 24 h at 70°C. HDPE irradiated at a high environmental temperature was more effective than that irradiated at a low environmental temperature in compatibilizing HDPE with PVA. Compared with the 83/17 HDPE/PVA blend, the yield and notched impact strength of the 73/17 HDPE/PVA blend compatibilized with 10% HDPE irradiated for 24 h at an environmental temperature of 70°C increased from 30.8 MPa and 110 J/m to 34.9 MPa and 142 J/m, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2966–2969, 2003     

Influence of maleic anhydride on the compatibility of thermal plasticized starch and linear low‐density polyethylene

In the presence of dicumyl peroxide, the compatibility of thermal plasticized starch/linear low‐density polyethylene (TPS/LLDPE) blends using maleic anhydride (MAH) as compatibilizer was investigated. The thermal plasticization of starch and its compatibilizing modification with LLDPE was accomplished in a single‐screw extruder at the same time. We prepared three types of blends containing different percentages of TPS and MAH. The content of MAH based on LLDPE was 0, 1, and 2 wt %, respectively. The morphology of the blends was studied by SEM. It was found that, with the addition of MAH, the blends have good interfacial adhesion and finely dispersed TPS and LLDPE phases, which is reflected in the mechanical and thermal properties of the blends. The blends containing MAH showed higher tensile strength, elongation at break, and thermal stability than those of blends without MAH. The rheologic properties of the blends demonstrated the existence of processing. Finally, the dynamic thermal mechanical analysis results indicated that, with the addition of MAH, the compatibility between TPS and LLDPE in the blends was substantially improved. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 686–695, 2004     

Degradation behavior of linear low‐density polyethylene films containing prooxidants under accelerated test conditions

This article reports the results of studies on the photooxidative and thermooxidative degradation of linear low‐density polyethylene (LLDPE) in the presence of cobalt stearate. Various amounts of cobalt stearate (0.1–0.9% w/w) blended with LLDPE and films of 70 ± 5 μ thickness were prepared by a film‐blowing technique. The films were subjected to xenon arc weathering and air‐oven aging tests (at 70°C) for extended time periods. We followed the chemical and physical changes induced as a result of aging by monitoring changes in the mechanical properties (tensile strength and elongation at break), carbonyl index, morphology (scanning electron microscopy), melt flow index, and differential scanning calorimetry crystallinity. Cobalt stearate was highly effective in accelerating the photodegradation of LLDPE films at concentrations greater than 0.2% w/w. The kinetic parameters of degradation, as determined by nonisothermal thermogravimetric analysis, were estimated with the Flynn–Wall–Ozawa isoconversion technique, which was subsequently used to determine the effect of cobalt stearate on the theoretical lifetime of LLDPE. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008