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     

Improvement of autohesive and adhesive properties of polyethylene plates by photografting with glycidyl methacrylate

Glycidyl methacrylate (GMA) was photografted with the low‐ and high‐density polyethylene (LDPE and HDPE) plates to provide their surfaces with autohesive and adhesive properties. The chemical composition and wettability of the GMA‐grafted LDPE and HDPE (LDPE‐g‐PGMA and HDPE‐g‐PGMA) plates remained constant above full coverage of the surfaces with grafted PGMA chains. Autohesive strength obtained with 1,4‐dioxane as a good solvent of PGMA increased with an increase in the grafted amount and substrate breaking was observed at the grafted amount of 117 μmol/cm². The grafted amount at substrate breaking was decreased by increasing the temperature and load during heat pressing. Adhesive strength was effectively enhanced by use of multi‐functional amine compounds because of the increase in the reaction between primary or secondary amine groups and epoxy groups appended to the grafted PGMA chains. In addition, the decrease in the amine compound concentration and the increase in the number of amino groups in the amine compounds used led to the decrease in the grafted amounts at substrate breaking. Substrate breaking occurred at lower grafted amounts for the HDPE‐g‐PGMA plates than for the LDPE‐g‐PGMA plates because the location of the photografting was restricted to the outer surface region for the HDPE plate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 493–500, 2007     

Investigation of polyethylene/sisal whiskers nanocomposites prepared under different conditions

In this work, sisal nanowhiskers (SNWs) extracted from sisal fibers were used to reinforce high‐density polyethylene (HDPE) and low‐density polyethylene (LDPE). The nanocomposites were prepared by solution casting from toluene and melt mixing, both followed by melt pressing. In the case of melt mixing, the surfaces of the SNW were also chemically modified with 1 phr of vinyl triethoxy silane to improve their dispersibility and compatibility with the matrices. The SNW had an average length of 197 nm and diameter of 12 nm, and a crystallinity index of 89%. Fourier transform infrared confirmed the surface chemical modification of the SNW. The whiskers were fairly well dispersed in the matrices, regardless of the treatment or preparation method. The presence of whiskers, as well as nanocomposite preparation method, had an observable influence on the storage modulus of LDPE, but very little influence on that of HDPE. There was, however, no significant influence on the degradation behavior of both polymers. The crystallization behavior of the polymers was found to strongly depend on their morphologies. The melting and crystallization behavior of the LDPE nanocomposites were almost unchanged, while an increase in crystallinity was observed for all the HDPE nanocomposites. The tensile properties depended on the type of polymer, the treatment, and the preparation method. Generally there was an improvement in tensile modulus, and a decrease in elongation at break, but the stress at break only improved for the HDPE nanocomposites. POLYM. COMPOS., 35:2221–2233, 2014. © 2014 Society of Plastics Engineers     

Self‐reinforcement of high‐density polyethylene/low‐density polyethylene prepared by oscillating packing injection molding under low pressure

This article reports the toughness improvement of high‐density polyethylene (HDPE) by low‐density polyethylene (LDPE) in oscillating packing injection molding, whereas tensile strength and modulus are greatly enhanced by oscillating packing at the same time. Compared with self‐reinforced pure HDPE, the tensile strength of HDPE/LDPE (80/20 wt %) keeps at the same level, and toughness increases. Multilayer structure on the fracture surface of self‐reinforced HDPE/LDPE specimens can be observed by scanning electron microscope. The central layer of the fracture surface breaks in a ductile manner, whereas the break of shear layer is somewhat brittle. The strength and modulus increase is due to the high orientation of macromolecules along the flow direction, refined crystallization, and shish‐kebab crystals. Differential scanning calorimetry and wide‐angle X‐ray diffraction find cocrystallization occurs between HDPE and LDPE. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 799–804, 1999     

Space charge distribution and crystalline structure in low density polyethylene (LDPE) blended with high density polyethylene (HDPE)

The space charge distribution in polyethylene blends under direct current electrical field was measured by a pulsed electro‐acoustic method. It was found that blending LDPE with 0.5 wt% HDPE decreased the amount of accumulated space charges and improved their distribution. Small‐angle light scattering and differential scanning calorimetry showed that crystallization of LDPE/HDPE started at higher temperature than virgin LDPE, and the sizes of LDPE/HDPE spherulites were smaller than that of LDPE. HDPE plays a role on nucleation during the crystallization process. Crystalline form was investigated by wide‐angle X‐ray diffraction and the results indicate that the crystal form did not change after blending. The reduction of space charges in the blended sample can be explained as the result of the dissipation of charges through boundary regions of smaller spherulites. Copyright © 2004 Society of Chemical Industry     

Phase structural analyses of polyethylene extrusion coatings on high‐density papers. I. Monoclinic crystallinity

In the present work the morphology of high‐density polyethylene (HDPE) extrusion coating layer on high‐density paper (HDP) has been investigated. An uneven layer with a high content of crystallinity against the paper surface was discovered. The methods applied were solid‐state ¹³C NMR Spectroscopy and Atomic Force Microscopy. The highly crystalline layer was found to be mainly monoclinic crystallinity. The formation of the monoclinic crystallites was probably initiated by orientation of the polyethylene molecules by drawing, adhesion to the fibrous paper surface, and pressure. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 218–225, 2004     

Effects of acid treatment at different temperatures on the surface dielectric properties of low‐density polyethylene

The surface dielectric properties of acid‐etched low‐density polyethylene (LDPE) were analysed in the frequency range from 20 Hz to 200 kHz. Samples were treated with various acids for a period of one hour, at temperatures ranging from 20 to 70 °C. After the treatment, the samples were analysed with Fourier transform infrared spectroscopy, revealing chemical and crystallinity changes on the surface, as a direct result of the treatment. The sample surfaces were analysed using atomic force microscopy. The micrographs show that the acid treatment increases the roughness of the samples. Compared to untreated LDPE, the etched samples may exhibit significantly different conductance values at low frequencies. It is also observed that an increase in the acid treatment temperature can result in lower values of conductance and susceptance compared to untreated samples. LDPE films with low value of surface AC conductivity after acid treatment are potentially useful substrates for high‐speed electro‐sensing applications. The presented results indicate that a suitable choice of acid treatment of LDPE can effect surface polarization while preserving low values of surface AC conductivity of the polymer. © 2014 Society of Chemical Industry     

Thermal characteristics and temperature profile changes of structurally different polyethylenes with peroxide modifications

Crosslinking and processing characteristics of polyethylenes (PEs) with different molecular architectures, namely high‐density polyethylene (HDPE), linear low‐density polyethylene (LLDPE), and low‐density polyethylene (LDPE), were studied with regard to the effects of peroxide modifications and coolant flow rates. Dicumyl peroxide (DCP) and di‐tert‐butyl peroxide (DTBP) were used as free‐radical inducers for crosslinking the PEs. The characteristics of interest included normalized gel content, real‐time temperature profiles and their cooling rates, exothermic period, crystallinity level, crystallization temperature, and heat distortion temperature. The experiments showed that LDPE exhibited the highest normalized gel content. The real‐time cooling rates, taken from the temperature profiles for all PEs before the crystallization region, were greater than those after the crystallization region. The cooling rate of the PEs increased with the presence of DCP, whereas the crystallization temperature of the PEs was lowered. The HDPE appeared to show the longest exothermic period as compared with those of the LLDPE and LDPE. The exothermic period showed an increase with increasing coolant flow rate, but it was decreased by the use of DCP. As for the effect of peroxide type, the gel content and cooling rate of the PE crosslinked by DCP were higher than those for the PE crosslinked by DTBP. The DTBP was the more effective peroxide for introducing crosslinks and simultaneously maintaining the crystallization behavior of the PE. J. VINYL ADDIT. TECHNOL., 20:80‐90, 2014. © 2014 Society of Plastics Engineers     

Uniaxial orientation of linear low density polyethylene

Only a few reported studies have involved the uniaxial orientation of LDPE and even less on LLDPE. It is our purpose to report on characteristics of uniaxially oriented films of LLDPE that contribute to property development. The LLDPE has been coextruded at 25 and at 80°C layered as ribbons within longitudinally split billets of HDPE. The LLDPE so drawn was characterized by thermal analysis, birefringence, elastic recovery, and wide angle X-ray measurements. As a result, we can conclude that the drawing of LLDPE at the lower temperature produces a relatively high content of monoclinic crystals; the orientation behavior of LLDPE is similar to that of HDPE. The molecular network formed by entanglements and crystals reduces the draw to a maximum below 15.     

HDPE/LDPE在动态保压注射成型中的自增强行为研究

研究了在ＨＤＰＥ中加入适量ＬＤＰＥ,经过动态保压注射成型,试样的强度与模量得到明显的提高,同时试样的韧性也较纯ＨＤＰＥ自增强试样韧性明显增加。ＨＤＰＥ／ＬＤＰＥ（８０／２０）自增强试样的拉伸强度与纯ＨＤＰＥ自增强试样的拉伸强度基本相当（拉伸强度１０８ＭＰａ）,而韧性有较大幅度的提高。ＳＥＭ观察可见拉伸断面为多层结构,断面的中心层为韧性断裂,而边缘剪切层为脆性断裂。ＤＳＣ和ＷＡＸＤ测试表明拉伸强度及模量的提高是由于大分子链沿流动方向的高度取向,晶粒的细化以及串晶的产生     

Study of polyethylene solution fractionation and resulting fractional crystallization behavior

Solution fractionation for four different polyethylenes including high‐density polyethylene (HDPE), low‐density polyethylene (LDPE), linear low‐density polyethylene (LLDPE), and very low‐density polyethylene (VLDPE) are conducted by stepwise controlling both the temperature and the amount of precipitant. The size exclusion chromatograph (SEC) measurements indicate that solution fractionation technique can successfully separate all the polyethylene samples in accordance with their molecular weight and molecular‐weight distributions. In addition, infrared spectroscopy analysis shows that the degree of short‐chain branching for each fraction of each polyethylene varies with the fraction's molecular weight. The effect of the molecular weight with different short‐chain branching on each fraction's crystallinity represents the characteristics of chain components for different polyethylenes. The crystallinities of HDPE, LLDPE, and LDPE decrease with the increase in their molecular weights; however, for VLDPE, its crystallinity increases with the increase in the molecular weight. The research revealed that the degree of short‐chain branching, together with the molecular weight, can greatly affect the crystallinity of polyethylene. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2542–2549, 2004     

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     

Carbon-Dioxide-Based Microsortation of Postconsumer Polyolefins and its Effect on Polyolefin Properties

Postconsumer polyolefin flake has been sorted using liquid carbon dioxide as a float-sink medium. This separation of PP and LDPE from HDPE was conducted at ambient temperature and a pressure that yielded a CO₂ specific gravity of 0.955, causing the HDPE to sink and the LDPE and PP to float. Although this process provided a high-purity (99+%) HDPE product stream, the effect of immersing the plastics in liquid carbon dioxide at these conditions was not previously measured. Therefore, six HDPE samples, two LDPE samples, and five PP samples were exposed to high-pressure carbon dioxide for 20 min. After this exposure, the polyolefins did not foam when the carbon dioxide was rapidly vented from the vessel. The weight reduction averaged 0.17%, which was attributed to the dissolution of low-molecular-weight additives or contaminants present on the surface of the plastics. No significant change in the melting point or latent heat of melting was observed, indicating that the degree of crystallinity was not affected by the exposure to carbon dioxide. No reduction was observed in the temperature at which the onset of thermal degradation occurred, because of the low solubility and degree of extraction of thermal stabilizers during the immersion in carbon dioxide. These results indicated that no deleterious effects on the polyolefin properties were associated with this separation technique.     

HDPE/LDPE复合交联物的热降解研究

采用热重分析仪（TG）考察了高密度聚乙烯（HDPE）／低密度聚乙烯（LDPE）复合交联物的热稳定性。结果显示，HDPE／LDPE复合交联物的热稳定性低于HDPE／LDPE共混物。FTIR分析证实，交联反应使聚乙烯（PE）的支化程度提高，取代基的位阻效应在一定程度上影响了PE的热降解过程。在N2气氛下，HDPE／LDPE共混物及交联物的热降解过程均为一步降解反应。Kissinger法求解HDPE／LDPE共混物及其复合交联物的热降解活化能发现，LDPE质量分数在20％～30％之间变化时，HDPE／LDPE交联物的热降解过程对温度的敏感性发生了突变。     

Determination of the degree of adhesion in plasma-treated polyethylene/paper laminates

It is shown that an oxygen or ammonia plasma treatment significantly improves the adhesion between low density polyethylene (LDPE) and cellulose. Plasma treatment of the polymer was more effective than treatment of the paper, and ammonia plasma seemed somewhat more effective than the oxygen treatment. The adhesion between polyethylene and cellulose was evaluated at room temperature using a non-linear double cantilever beam test. The effect of the discharge treatment on the surface composition of LDPE and cellulose was characterized using electron spectroscopy for chemical analysis. The improved adhesion may be due to an improved penetration of the porous paper surface by the LDPE-melt and to an increase in the interfacial attraction forces as a result of the introduction of polar groups in the surfaces.     

Improvement of the polarity of polyethylene with oxidized Fischer–Tropsch paraffin wax and its influence on the final mechanical properties

The easy, low‐cost modification of the polarity of low‐density polyethylene (LDPE) and high‐density polyethylene (HDPE) through blending with oxidized Fischer–Tropsch wax was investigated. A 10 wt % concentration of the wax increased the polar component of the total surface free energy 10 times for LDPE and 4.5 times for HDPE. Modified LDPE also had significantly higher adhesion to the polar substrate, which was represented by a crosslinked epoxy‐based resin. This behavior was not observed for HDPE. The conservation of the good mechanical properties of polyethylene was observed. The wax content had only a moderate influence on the mechanical properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1164–1168, 2005     

Preparation and anti‐icing property of a lotus‐leaf‐like superhydrophobic low‐density polyethylene coating with low sliding angle

A lotus‐leaf‐like superhydrophobic low‐density polyethylene (LDPE) coating with low sliding angle was prepared by a facile method. The water contact angle and sliding angle of the as‐prepared superhydrophobic LDPE coating were 156 ± 1.7° and 1°, respectively. The anti‐icing property of the as‐prepared LDPE coating with low sliding angle was investigated in a climatic chamber with a working temperature of ?5°C. The results showed that the superhydrophobic LDPE coating with low sliding angle can largely prevent ice formation on the surface, showing excellent anti‐icing property. The as‐prepared superhydrophobic LDPE coating with good anti‐icing property will be perfectly desirable for outdoor equipments to reduce ice formation on their surfaces in cold seasons. This work will provide a new way to fabricate anti‐icing coating and thus find applications in a variety of fields. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Adhesion of polyethylene plates photografted with methacrylic acid and acrylic acid with enzymatically modified chitosan solutions and X‐ray photoelectron spectroscopy analysis of failed surfaces

An investigation was carried out on the application of dilute chitosan solutions modified by a tyrosinase‐catalyzed reaction with 3,4‐dihydroxyphenetylamine (dopamine) to the adhesion of low‐density polyethylene (LDPE) and high‐density polyethylene (HDPE) plates photografted with carboxyl‐group‐containing hydrophilic monomers, such as methacrylic acid (MAA) and acrylic acid (AA). In the case where photografting was carried out at lower monomer concentrations or at lower temperatures, the adhesive strength sharply increased with lower grafted amounts. A sharp increase in the adhesive strength was found to be due to the formation of shorter grafted polymer chains at lower monomer concentrations and/or the restriction of the location of grafting to the outer surface region at lower temperatures. In addition, the adhesive strength also sharply increased at even lower grafted amounts for photografting onto the HDPE plates and/or that of AA because the location of grafting was restricted to the outer surface region. For the AA‐grafted LDPE and HDPE plates, substrate breaking was observed. This was attributed to the coverage of the substrate surfaces with grafted poly(acrylic acid) chains at lower grafted amounts and a high water absorptivity of the grafted layer. X‐ray photoelectron spectroscopy (XPS) analysis of the grafted LDPE plates incubated in a dopamine solution containing tyrosinase suggested that the increase in the adhesive strength was caused by the penetration of enzymatically modified chitosan solutions in the grafted layers and the subsequent reaction of quinone derivatives enzymatically generated with grafted polymer chains. In addition, the surface analysis of the failed surfaces by XPS showed that as the adhesive strength increased, the location of failure was shifted from the interface between the layers mixed with enzymatically modified chitosan materials and grafted polymer chains to the inside the grafted layer containing enzymatically modified chitosan materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Development and physico‐mechanical behavior of LDPE–sisal prepreg‐based composites

Low‐density polyethylene (LDPE)‐coated sisal fiber prepreg was prepared by using solution coating process. These coated fiber prepregs were consolidated to make composites having different weight fraction of sisal fibers in a hot compression‐molding machine. This experimental study reveals that higher loading of sisal fiber up to 57wt% in LDPE–sisal composites is possible by this technique. Mechanical and abrasive wear characteristics of these composites were determined. The tensile strength of composites increased with the increase in sisal fiber concentration. Coating thickness of LDPE was varied by changing the viscosity of LDPE–xylene solution that manifested to different weight fraction of fiber in sisal–LDPE composites. Mechanical, dynamic mechanical, and abrasive wear characteristics of these composites were determined. The tensile strength and modulus of sisal composites reached to 17.4 and 265 MPa, respectively, as compared to 7.1 and 33MPa of LDPE. Storage modulus of sisal composites LD57 reached to 2.7 × 10⁹ MPa at 40°C as compared to 8.1 × 10⁸ MPa of LDPE. Abrasive wear properties of LDPE and its composites were determined under multi‐pass mode; pure LDPE showed minimum specific wear rate. The specific wear rate of composites decreased with the sliding distance. Increase of coated sisal fiber content increased the specific wear rate at all the sliding distances, which has been explained on the basis of worn surface microstructures observed by using SEM. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Improvement in adhesive‐free adhesion by the use of electrostatic interactions between polymer chains grafted onto polyethylene plates

The tensile shear adhesive‐free adhesion properties induced by electrostatic interactions between poly(acrylic acid) (PAA) and poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA) chains grafted onto polyethylene (PE) with low‐density (LDPE) or high‐density (HDPE) plates were studied. PAA‐ or PDMAEMA‐grafted PE plates were immersed in a HCl or NaOH solution or water for 24 h, and their electrostatic properties were changed before they were overlapped with each other and heat‐pressed. The breaking of the substrate between the two plates with water‐swollen grafted layers was observed in the low range of grafted amounts in comparison with immersion in the acidic and basic solutions. The ability of the two plates with grafted polymer chains swollen in water to strongly bond with each other was a result of electrostatic interactions formed by positively charged PDMAEMA and negatively charged PAA chains. The breaking of the substrate in the case of adhesive‐free adhesion between quaternized PDMAEMA‐grafted and PAA‐grafted PE plates immersed in the basic solution occurred with lower grafted amounts of PAA. This came from the strong attractive force between dissociated anionic PAA chains and quaternized cationic PDMAEMA chains in the basic solution. In addition, the adhesive‐free adhesion strength of HDPE plates with the same grafted polymer chains encountered the breaking of the substrate with lower grafted amounts than that of LDPE plates. It was concluded that the grafting of polymer chains onto HDPE plates with high crystallinity was considerably restricted to the outer surface regions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2632–2638, 2006