Phase structural analyses of polyethylene extrusion coatings on high‐density papers. II. Influence of paper surface properties on the polyethylene morphology

Paper samples of three different qualities were extrusion coated with low‐density polyethylene (LDPE) and high‐density polyethylene (HDPE). The morphological phases of the polyethylene layers have been quantified by ¹³C solid‐state high‐resolution NMR. Shear forces in the process initiate the formation of the monoclinic crystallites. The surface tensions of the high‐density papers have influence on the degree of interaction between the two materials and how these shear forces work. The paper surface properties will thus have an influence on properties and the size of the monoclinic crystalline mass fraction of the polyethylene coating. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 226–234, 2004     

Phase structural analyses of polyethylene coatings on high‐density papers. III. Determination of the crystallite thicknesses by T1 measurements

Two different extrusion‐coating qualities of polyethylene, namely LDPE and HDPE, were coated on high‐density papers. Differences were observed with respect to their response to storage and low temperature heat treatment. HDPE does not respond to storage at ambient temperature and heat treatment in the same way as LDPE. The LDPE‐coating exhibits an increase in the monoclinic crystalline fraction at the paper surface as a result of heat treatment. The nature of this response appears to be a result of adhesion to a paper surface, the properties of this surface, orientation of polymer chains, and chain mobility differences. The increase of the monoclinic fraction is shown to relate to an increase of the mean crystallite thickness and initiation of new crystallites at the paper surface. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 235–241, 2004     

Optimization of polyethylene/binder/polyamide extrusion blow‐molded films. III. Slippability improvement with fatty acid amides

The slippability of packaging films has to be controlled to facilitate confectionary operations and guarantee an easy opening for filling. In the case of single‐layer polyethylene (PE) films, the addition of slip agents made of fatty acid amides such as erucamide or oleamide usually allows the tailoring of the coefficient of friction (COF) in the film to match industrial targets, which depend on the final application. The coupling of Fourier transform infrared spectroscopy and atomic force microscopy analysis showed that this method has a limited efficiency and may even be detrimental in the case of multilayer PE + ethylene vinyl acetate (EVA)/maleic anhydride grafted polyethylene (PEgMAH) + EVA/polyamide films. The reason is that the migration of the slip additives toward the outermost surface of the PE layer, which leads to a reduction in the COF, are strongly affected by both the existence of the adjacent layers and the presence of EVA in the PE and PEgMAH layers. Nevertheless, a proper knowledge of the effect of this perturbation allows one to reach a slippability level that is required for some confectionary operations and/or for an easy opening for filling without the degradation of the heat sealability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crosslinking of low‐density polyethylene by diisocyanates for superior barrier properties

The chemical modification of low‐density polyethylene (LDPE) resins with hexamethylene diisocyanate and toluene diisocyanate was achieved. The reaction of LDPE with diisocyanate was monitored by Fourier transform infrared spectroscopy, wherein the appearance of new peaks at 3326, 1620, and 1572 cm^?1 corresponding to ? N? H stretching, ? (C?O)? NH₂ stretching, and ? N? H bending in an amide moiety, respectively, was observed. Modified films of excellent clarity and uniform thickness were obtained by the solution casting of crosslinked polyethylene. The oxygen transmission rate (OTR), water vapor transmission rate (WVTR), grease resistance, and thermal properties of the modified films were studied. The results clearly indicate that the OTR was improved by 35% and that grease resistance was improved by 90–125% in the crosslinked LDPE films with little change in their strengths. The heat seal characteristics, however, showed that relatively higher temperatures were needed to achieve efficient sealing in these films. Differential scanning calorimetry showed a decrease in the melting temperature from 104°C for LDPE to 101°C for both of the crosslinked LDPE films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1193–1199, 2005     

Surface chemistry and mechanical property changes of wood‐flour/high‐density‐polyethylene composites after accelerated weathering

Although wood–plastic composites have become more accepted and used in recent years and are promoted as low‐maintenance, high‐durability building products, they do experience a color change and a loss in mechanical properties with accelerated weathering. In this study, we attempted to characterize the modulus‐of‐elasticity (MOE) loss of photostabilized high‐density polyethylene (HDPE) and composites of wood flour and high‐density polyethylene (WF/HDPE) with accelerated weathering. We then examined how weathering changed the surface chemistry of the composites and looked at whether or not the surface changes were related to the MOE loss. By examining surface chemistry changes, we hoped to begin to understand what caused the weathering changes. The materials were left unstabilized or were stabilized with either an ultraviolet absorber or pigment. After 1000 and 2000 h of accelerated weathering, the samples were tested for MOE loss. Fourier transform infrared (FTIR) spectroscopy was employed to monitor carbonyl and vinyl group formation at the surface. Changes in the HDPE crystallinity were also determined with FTIR techniques. It was determined that structural changes in the samples (carbonyl group formation, terminal vinyl group formation, and crystallinity changes) could not be reliably used to predict changes in MOE with a simple linear relationship. This indicated that the effects of crosslinking, chain scission, and crystallinity changes due to ultraviolet exposure and interfacial degradation due to moisture exposure were interrelated factors for the weathering of HDPE and WF/HDPE composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2263–2273, 2004     

Ultraviolet preirradiation of high‐density polyethylene for the grafting of maleic anhydride during reactive extrusion

High‐density polyethylene was irradiated with ultraviolet light for various exposure times, as a prestep for hydroperoxide production, before a bulk grafting reaction with maleic anhydride in the melt phase by reactive extrusion. This method was compared with a traditional grafting procedure using peroxides optimized by an evaluation of the grafting level versus the screw speed; the highest speed showed the greatest grafting value. The reaction was followed by Fourier transform infrared, the gel percentage, and the grafting degree, which was evaluated by titration. The effect of grafting for both methods under the established processing conditions on the thermal properties was observed with differential scanning calorimetry via their heating and cooling thermograms; there were notorious changes in the fusion peak temperatures, indicating differences in the crystallization process after the grafting reaction. The latter was confirmed by NMR spectroscopy, which showed succinic anhydride rings attached to the polyethylene chains. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2882–2888, 2006     

Organic‐acid‐catalyzed sol–gel route for preparing poly(methyl methacrylate)–silica hybrid materials

In this study, a series of organic–inorganic hybrid sol–gel materials consisting of a poly(methyl methacrylate) (PMMA) matrix and dispersed silica (SiO₂) particles were successfully prepared through an organic‐acid‐catalyzed sol–gel route with N‐methyl‐2‐pyrrolidone as the mixing solvent. The as‐synthesized PMMA–SiO₂ nanocomposites were subsequently characterized with Fourier transform infrared spectroscopy and transmission electron microscopy. The solid phase of organic camphor sulfonic acid was employed to catalyze the hydrolysis and condensation (i.e., sol–gel reactions) of tetraethyl orthosilicate in the PMMA matrix. The formation of the hybrid membranes was beneficial for the physical properties at low SiO₂ loadings, especially for enhanced mechanical strength and gas barrier properties, in comparison with the neat PMMA. The effects of material composition on the thermal stability, thermal conductivity, mechanical strength, molecular permeability, optical clarity, and surface morphology of the as‐prepared hybrid PMMA–SiO₂ nanocomposites in the form of membranes were investigated with thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, gas permeability analysis, ultraviolet–visible transmission spectroscopy, and atomic force microscopy, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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     

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     

Degradation of polyethylene during extrusion. II. Degradation of low‐density polyethylene,linear low‐density polyethylene,and high‐density polyethylene in film extrusion

The degradation of different polyethylenes—low‐density polyethylene (LDPE), linear low‐density polyethylene (LLDPE), and high‐density polyethylene (HDPE)—with and without antioxidants and at different oxygen concentrations in the polymer granulates, have been studied in extrusion coating processing. The degradation was followed by online rheometry, size exclusion chromatography, surface oxidation index measurements, and gas chromatography–mass spectrometry. The degradations start in the extruder where primary radicals are formed, which are subject to the auto‐oxidation when oxygen is present. In the extruder, crosslinking or chain scissions reactions are dominating at low and high melt temperatures, respectively, for LDPE, and chain scission is overall dominating for the more linear LLDPE and HDPE resins. Additives such as antioxidants react with primary radicals formed in the melt. Degradation taking place in the film between the die orifice, and the quenching point is mainly related to the exposure time to air oxygen. Melt temperatures above 280°C give a dominating surface oxidation, which increases with the exposure time to air between die orifice and quenching too. A number of degradation products were identified—for example, aldehydes and organic acids—which were present in homologous series. The total amount of aldehydes and acids for each number of chain carbon atoms were appeared in the order of C5>C4>C6>C7?C2 for LDPE, C5>C6>C4>C7?C2 for LLDPE, and C5>C6>C7>C4?C2 for HDPE. The total amounts of oxidized compounds presented in the films were related to the processing conditions. Polymer melts exposed to oxygen at the highest temperatures and longest times showed the presence dialdehydes, in addition to the aldehydes and acids. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1525–1537, 2004     

Effect of initial crystallinity on the response of high‐density polyethylene to high‐energy radiation

Samples of each of two high‐density polyethylenes with various initial degrees of crystallinity, but otherwise identical, were exposed under a vacuum to moderate doses of gamma irradiation. The results indicate that, for otherwise initially identical polymer samples, the dose required to reach the gel point increases with increase of the initial degree of crystallinity. Above the critical dose for gelation, the gel content decreases with higher degrees of crystallinity at equal radiation doses. The mechanical behavior of the polymers changed progressively from ductile to brittle as the crystallinity was increased. The extensibility of originally ductile samples decreases with increasing radiation dose. The irradiation of samples having intermediate behavior produces a change to ductile behavior. Mechanical behavior is not modified substantially when brittle samples are irradiated. The initial modulus is little altered by irradiation, while the yield stress shows a slight increase with irradiation. The mechanical properties, such as draw ratio at break and ultimate tensile stress, decrease with dose in ductile samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1375–1384, 1999     

Polyethylene composite fibers. I. Composite fibers of high‐density polyethylene

Polymer matrix composites are generally studied in the form of bulk solids, and very few works have examined composite fibers. The research described here extended such bulk studies to fibers. The question is whether or not what has been reported for bulk polymers will be the same in fibers. In this article are reported studies of high‐density polyethylene (HDPE), whereas those of linear low‐density polyethylene are reported in part II of this article series. Two types of filler were used, that is, organically modified montmorillonite (OMMT), in which the nanosized filler particles had a high aspect ratio, and microsized calcium carbonate (CaCO₃), with an aspect ratio nearer to unity. Composite fibers of both as‐spun and highly drawn forms were prepared, and their structures, morphology, and mechanical properties were studied. It was found that the microsized particles gave HDPE composite fibers with mechanical properties that were the same as those of the neat polymer. In the case of clay composite fibers, the clay interfered with the yield process, and the usual yield point could not be observed. The particle shape did not affect the mechanical properties. The fibers showed different deformation morphologies at low draw ratios. The CaCO₃ composite fibers showed cavities, which were indicative of low interaction between the polymer and the filler. The OMMT composite fibers showed platelets aligned along the fibers and good polymer–filler interaction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of the high‐density polyethylene melt index on the microcellular foaming of high‐density polyethylene/polypropylene blends

The effect of high‐density polyethylene (HDPE)/polypropylene (PP) blending on the crystallinity as a function of the HDPE melt index was studied. The melting temperature and total amount of crystallinity in the HDPE/PP blends were lower than those of the pure polymers, regardless of the blend composition and melt index. The effects of the melt index, blending, and foaming conditions (foaming temperature and foaming time) on the void fractions of HDPEs of various melt indices and HDPE/PP blends were also investigated. The void fraction was strongly dependent on the foaming time, foaming temperature, and blend composition as well as the melt index of HDPE. The void fraction of the foamed 30:70 HDPE/PP blend was always higher than that of the foamed 50:50 HDPE/PP blend, regardless of the melt index. The microcellular structure could be greatly improved with a suitable ratio of HDPE to PP and with foaming above the melting temperature for long enough; however, using high‐melt‐index HDPE in the HDPE/PP blends had a deleterious effect on both the void fraction and cell morphology of the blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 364–371, 2004     

Crosslinking of high‐density polyethylene in the presence of organic peroxides

The crosslinking efficiency of various commercially available organic peroxides (dicumyl peroxide, O,O‐t‐butyl O‐2‐ethylhexylperoxycarbonate, t‐butyl peroxybenzoate, t‐butyl 3,5,5‐trimethylperoxyhexanoate, and t‐butyl 2‐ethylperoxyhexanoate) was tested on high‐density polyethylene (HDPE) in its molten state. The variations of the concentrations of the peroxides versus the crosslinking extent were plotted for these peroxides, and the values were compared. Dicumyl peroxide was found to be the best crosslinking agent for HDPE. The efficiency of the HDPE crosslinking with each peroxy derivative was analyzed on the basis of the behavior of the radicals generated from it. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 75–81, 2004     

Studies on blends of high‐density polyethylene and polypropylene produced by oscillating shear stress field

Tensile strength and morphology of blends of high‐density polyethylene (HDPE) and polypropylene (PP) obtained by oscillating packing injection molding were investigated via Universal Testing Machine, DSC, and SAXS. Tensile strength is greatly enhanced from 24.5 MPa to more than 90 MPa for pure HDPE and for blends with PP content less than 10 wt %. There exists a sharp decrease of tensile strength when PP content is more than 10 wt %. The shear‐induced morphologies with core in the center, oriented zone surrounding the core and skin layer are observed in the cross‐section areas of the samples. Interestingly, a sharp decrease of oriented zone is seen when PP content is more than 10 wt %, associated with the sharp decrease of tensile strength. DSC result shows double melting peaks with a high‐temperature melting peak that is not present in the endotherm obtained from the central core and obtained from the samples by static packing injection molding, which indicates the existence of shish‐kebab structure in the oriented zone. However, there is no difference of crystallinity between the samples by oscillating and by static packing injection molding. SAXS was used to analyze the complicated morphologies induced by shear stress, and results show that the crystal thickness could be greatly increased under shear stress. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 58–63, 2002     

Thermal analysis of high‐density polyethylene and low‐density polyethylene with enhanced biodegradability

The thermal properties of high‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) filled with different biodegradable additives (Mater‐Bi AF05H, Cornplast, and Bioefect 72000) were investigated with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The DSC traces of the additives indicated that they did not undergo any significant phase change or transition in the temperature region typically encountered by a commercial composting system. The TGA results showed that the presence of the additive led to a thermally less stable matrix and higher residue percentages. The products obtained during the thermodegradation of these degradable polyolefins were similar to those from pure polyethylenes. The LDPE blends were thermally less stable than the HDPE blends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 764–772, 2002     

Reactive extrusion for the synthesis of nylon 12 and maleated low‐density polyethylene blends via the anionic ring‐opening polymerization of lauryllactam

Nylon 12 was successfully synthesized in a twin‐screw extruder via the anionic ring‐opening polymerization of lauryllactam (LL). Maleated low‐density polyethylene (LDPE–MAH) was added to improve the mechanical properties of nylon 12. The in situ blends of nylon 12 and LDPE–MAH were characterized by mechanical testing and scanning electron microscopy. With increasing LDPE–MAH content, the tensile strength and flexural strength decreased, whereas the blend had improved impact strength and achieved supertoughness when the content of LDPE–MAH was 30 wt %. In the in situ formed low‐density polyethylene‐g‐PA12 copolymer, the domain of the LDPE–MAH phase was finely dispersed in the nylon 12 matrix. The good interface between the two phases demonstrated that LDPE–MAH could be used as a macromolecular activator to induce the polymerization of LL. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Ultraviolet weathering of photostabilized wood‐flour‐filled high‐density polyethylene composites

Wood‐plastic composites are being increasingly examined for nonstructural or semistructural building applications. As outdoor applications become more widespread, durability becomes an issue. Ultraviolet exposure can lead to photodegradation, which results in a change in appearance and/or mechanical properties. Photodegradation can be slowed through the addition of photostabilizers. In this study, we examined the performance of wood flour/high‐density polyethylene composites after accelerated weathering. Two 2⁴ factorial experimental designs were used to determine the effects of two hindered amine light stabilizers, an ultraviolet absorber, a colorant, and their interactions on the photostabilization of high‐density polyethyl‐ ene blends and wood flour/high‐density polyethylene composites. Color change and flexural properties were determined after 250, 500, 1000, and 2000 h of accelerated weathering. The results indicate that both the colorant and ultraviolet absorber were more effective photostabilizers for wood flour/high‐density polyethylene composites than the hindered amine light stabilizers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2609–2617, 2003     

Bi‐axial self‐reinforcement of high‐density polyethylene induced by high‐molecular weight polyethylene through dynamic packing injection molding

Previously, bi‐axial self‐reinforcement of high‐density polyethylene (HDPE) was achieved through a uni‐axial shear stress field introduced by dynamic packing injection molding technology. Here, further improvement of tensile strength along the flow direction (MD) was achieved by blending a small amount of high‐molecular‐weight polyethylene (HMWPE) with HDPE, while the tensile strength along the transverse direction (TD) still substantially exceeded that of conventional moldings. Tensile strengths in both flow and transverse directions were considerably enhanced, with improvements from 23 MPa to 76 MPa in MD and from 23 MPa to 31 MPa in TD. The effect of HMWPE content and molding parameters on tensile properties was also investigated. The tensile strength along MD was highly dependent on HMWPE content, oscillating cycle, mold temperature, melt temperature and packing pressure, while that along TD was insensitive to composition and processing parameters within the selected design space. According to the stress–strain curves, samples with HMWPE produced by dynamic packing injection molding had a special tensile failure mode in MD, different from both typical plastic and brittle failure modes. There were no yielding and necking phenomena, which are characteristic during tensile testing of plastic materials, but there was still a considerably higher elongation compared to those of brittle materials. However, in TD, all dynamic injection molding samples exhibited plastic failure as did typical conventional injection molding samples. Copyright © 2006 Society of Chemical Industry