An improvement on the adhesion‐strength of laminated ultra‐high‐molecular‐weight polyethylene fabrics: surface‐etching/modification using highly effective helium/oxygen/nitrogen plasma treatment

In this study, helium/oxygen/nitrogen (He/O₂/N₂)‐plasma was used to etch/modify the surface of ultra‐high‐molecular‐weight polyethylene (UHMWPE) fiber. After coated with polyurethane (PU), the plasma treated UHMWPE fabrics were laminated. It was found that the values of peeling strength between the laminated UHMWPE fabrics treated with He/O₂/N₂‐plasma were significantly higher (3–4 times) than that between pristine fabrics. The hydrophilic property and the value of the surface roughness of the UHMWPE fibers increased significantly after treated with He/O₂/N₂‐plasma. The mechanism of the oxidation/degradation of the polymers on the surface of the UHMWPE fiber during He/O₂/N₂‐plasma treatment was suggested. In addition, it was found that the higher content of functional groups (carbonyl, aldehyde, and carboxylic acid) on fiber surface and the higher value of surface roughness of the UHMWPE fiber treated with He/O₂/N₂‐plasma could significantly improve the adhesion‐strength of the laminated UHMWPE fabric. Especially, the micro‐aperture on the surface of UHMWPE fiber caused by the strenuous etching of He/O₂/N₂‐plasma treatment was also an important factor on improving the adhesion‐strength between the laminated UHMWPE fabrics. Copyright © 2010 John Wiley & Sons, Ltd.     

Morphology and mechanical properties of blown films of a low‐density polyethylene/linear low‐density polyethylene blend

The morphologies of films blown from a low‐density polyethylene (LDPE), a linear low‐density polyethylene (LLDPE), and their blend have been characterized and compared using transmission electron microscopy, small‐angle X‐ray scattering, infrared dichroism, and thermal shrinkage techniques. The blending has a significant effect on film morphology. Under similar processing conditions, the LLDPE film has a relatively random crystal orientation. The film made from the LDPE/LLDPE blend possesses the highest degree of crystal orientation. However, the LDPE film has the greatest amorphous phase orientation. A mechanism is proposed to account for this unusual phenomenon. Cocrystallization between LDPE and LLDPE occurs in the blowing process of the LDPE and LLDPE blend. The structure–property relationship is also discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 507–518, 2002; DOI 10.1002/polb.10115     

Protective encapsulation of acid‐sensitive catalysts using polyethylene ligands

The stability of polyethylene oligomer (PE_Olig)‐entrapped salen‐metal complexes toward acidolysis is described. These complexes dissolve in hot toluene and precipitate as hydrophobic powders. The salen species in these precipitates or in precipitates of admixtures of oligomeric complexes and unfunctionalized polyethylene are stable to acid when suspended in acidic methanol for 24 h at 25°C. The lack of metal leaching due to acid‐promoted demetalation was determined using both colorimetric and ICP‐MS analyses. The ICP‐MS results showed the amount of metal loss for PE_Olig‐salen‐metal complexes was 0.27%, 0.45%, and 0.79% for half‐salen Cr(III), salen Cr(III), and salen Mn(III) complexes, respectively. These results were in contrast to the reported behavior of low molecular weight salen metal complexes and to results seen with a salen complex bound to divinylbenzene (DVB) crosslinked polystyrene which demetalates under acidic conditions at room temperature. Salen complexes formed with PE_Olig complexes also demetalate when the PE_Olig‐bound species are in solution at elevated temperature and exposed to acid. These results show that as solids oligomeric polyethylene ligands even without added PE can serve as a protective encapsulating matrix for the solid forms of polymer‐supported catalysts. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Electrospinning of ultrahigh‐molecular‐weight polyethylene nanofibers

The electrospinning method has been employed to fabricate ultrafine nanofibers of ultrahigh‐molecular‐weight polyethylene for the first time with a mixture of solvents of different dielectric constants and conductivities. The possibility of producing highly oriented nanofibers from ultrahigh‐molecular‐weight polymers suggests new ways of fabricating ultrastrong, porous, and single‐component nanocomposite fibers with improved properties. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 766–773, 2007     

Modeling of the linear viscoelastic behavior of low‐density polyethylene

We predict the linear viscoelastic behavior of low‐density polyethylene from both the molecular‐weight distribution and the individual structure of each species in the sample. The “structure map” of the samples was derived from SEC measurements. This map is a three‐dimensional representation of the seniority distribution, and represents the probability of existence of a segment with seniority i in a molecule of molecular weight M. Moreover, results from the kinetics of the free radical polymerization of polyethylene show that the molecular weight of the segments increases according to their seniority. Finally, tube dilatation was generalized to the case of polydisperse samples. The solvent behavior of the relaxed segments was included through a continuous function of time that describes the instantaneous state of the entanglement network in the sample. The comparison between the theoretical predictions and the experimental data shows a good agreement over the whole experimental frequency range. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43:1973–1985, 2005     

Surface treatment of ultra‐high molecular weight polyethylene fibers using potassium permanganate and mechanical properties of its composites

Potassium permanganate was applied to improve the surface properties of the ultra‐high molecular weight polyethylene (UHMWPE) fibers. The results suggested that the surface oxygen atoms increased dramatically and the O/C ratio increased from 0.030 to 0.563 after treatment. The increased surface roughness and the O‐containing groups on the treated fiber surface decreased the contact angles with water and ethylene glycol. The crystallinity and the crystallite size of the treated fibers increased, and the DSC results indicated that chain scission and the formation of ―C═O chemical defects in the amorphous region were the main mechanisms of the deterioration of the treated UHMEPE fibers. The breaking strength and the elongation at break of the fibers decreased, but the modulus increased after treatment. The treated fibers exhibited better adhesion with epoxy matrix. An improvement of 27.6% from 101.4 to 129.4 MPa in ILSS confirmed the improvement in the interfacial adhesion strength of composites. The impact and bending strength of composites were both improved.     

Design of aluminum trihydroxide and P‐N core‐shell structures and their synergistic effects on halogen‐free flame‐retardant polyethylene composites

In order to improve the performance of inorganic/organic composites, aluminum trihydroxide (ATH) core composites with a styrene‐ethylene‐butadiene‐styrene block copolymer grafted with maleic anhydride (MAH‐g‐SEBS) shell phase, and P‐N flame retardant as a synergistic agent, were prepared through an interface design. The effects of polyethylene glycol (PEG) content on the interfacial interaction, flame retardancy, thermal properties, and mechanical properties of high‐density polyethylene (HDPE)/ATH composites were investigated by small angle X‐ray diffraction, rotational rheometer, limiting oxygen index, thermogravimetric analysis (TGA), and tensile testing. The ATH synergistic effects of P‐N flame‐retardant improved the combustion performance of HDPE/ATH/PEG(3%)/MAH‐g‐SEBS/P‐N (abbreviated as HDPE/MH3/M‐g‐S/P‐N) composite by forming more carbon layer, increased the elongation at break from 21% to 558% compared to HDPE/ATH, and increased the interface thickness from 0.447 to 0.891 nm. SEM results support the compatibility of ATH with HDPE increased and the interfacial effect was enhanced. TGA showed the maximum decomposition temperature of the two stages and the yield of the residue at high temperature increased first and then decreased with the increase of PEG content. Rheological behavior showed the storage modulus, complex viscosity, and the relaxation time initially increased and then decreased with the increase of PEG content indicating PEG, M‐g‐S, and ATH powder gradually formed a partial coating, then a full coating, and finally an over‐coated core‐shell structured model.     

Assessing the transport properties of organic penetrants in low‐density polyethylene using free volume models

Three models, two of them relying on free volume—the Cohen–Turnbull–Fujita (CTF) model and the Vrentas–Duda (VD) model, and the third being empirical using an exponential concentration dependence of the diffusivity, were applied to desorption data for a series of alkane penetrants (2,2‐dimethylbutane, cyclohexane, n‐hexane, n‐decane, and n‐tetradecane) in low‐density polyethylene. The CTF model described the desorption data very well and better than the exponential diffusion law. The VD model with the attractive feature of being based on independently determined parameters was unsuccessful in describing the desorption data. Diffusivity data indicated that the three components outside the crystal core were less accessible to n‐tetradecane than to the other penetrants. This indication was further substantiated by solubility data. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 723–734, 2007     

Vinyl/Vinylene functionalized highly branched polyethylene waxes obtained using electronically controlled cyclohexyl‐fused pyridinylimine‐nickel precatalysts

A series of 8‐(2,6‐dibenzhydryl‐4‐R‐phenylimino)‐5,6,7‐trihydroquinoline ligands have been prepared in which the nature of 4‐R substitutions vary from electron withdrawing to electron donating. The treatment with NiCl₂.6H₂O or (DME)NiBr₂ afforded the corresponding complexes of nickel chloride (4‐R = Me Ni1 , Et Ni2 , ^tBu Ni3 , CHPh₂ Ni4 , Cl Ni5 , and F Ni6 ) and nickel bromide (4‐R = Me Ni7 , Et Ni8 , ^tBu Ni9 , CHPh₂ Ni10 , Cl Ni11 , and F Ni12 ). X‐ray diffraction study of complexes Ni3 , Ni6 , and Ni10 , revealed that Ni3.1/2H₂O and Ni6.H₂O adopted unsymmetrical and symmetrical chloride‐bridged dinuclear structures respectively, while Ni10.H₂O is found as mononuclear specie forming distorted‐square planer geometry. In the presence of either diethylaluminum chloride (Et₂AlCl) or modified methylaluminoxane (MMAO), all the nickel complexes ( Ni1–Ni12 ) displayed high activities (up to 1.91 × 10⁶ g(PE) mol (Ni)⁻¹h⁻¹. Highly branched polyethylene waxes with low molecular weights (M_w ≤ 2.6 kg/mol) and narrow molecular weights distributions (M_w/M_n ≤ 1.96) incorporated with vinylene and vinyl groups were obtained. The effects of 4‐R substitutions to the nickel chloride and bromide pre‐catalysts and reaction conditions on the catalytic performance and the properties of the resulting polyethylene were the subject of a detail investigation. The positive influences of using electron‐withdrawing 4‐R substitutions and bromides were observed. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1269–1281     

High‐density polyethylene/expanded graphite nanocomposites produced by polymerization‐filling technique using an industrial heterogeneous catalyst

High‐density polyethylene nanocomposites with different expanded graphite (EG) contents (0.34–1.80 wt %) were prepared by polymerization‐filling technique using an industrial heterogeneous catalyst ( cat K ), and characterized using a range techniques: melting flow index (MFI), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and transmission electron microscopy (TEM). The MFI data showed that EG acts as a plasticizer decreasing melt viscosity in comparison to neat HDPE produced exclusively by cat K . DSC results showed that EG nucleated the HDPE crystallization as established by the increased crystallization temperature, and the degree of crystallinity. HDPE/EG nanocomposites displayed a significant improvement in the flexural (increased from 1458 to 1831 MPa), and storage modulus (increased from 122 to 1627 MPa) at only 1.80 wt % EG content. TEM images confirmed a homogeneous distribution of EG into the polymer matrix with the presence of dispersed, intercalated and aggregated EG nanofillers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1260–1267     

In situ synthesis of polyethylene terephthalate nanocomposites using bis (2‐hydroxyethyl) phthalate monomer

In this article, we address in situ synthesis of polyethylene terephthalate (PET) nanocomposites using the bis (2‐hydroxyethyl) phthalate monomer and inorganic layered materials (sulfanilic acid salt‐modified magnesium aluminum‐layered double hydroxides [MgAl LDH‐SAS] and Dimethyloctadecyl [3‐(trimethoxysilyl) propyl] ammonium chloride [DTSACl] and tetraethyl orthosilicate [TEOS]‐ modified clay [CL120‐DT]). The dispersion morphology of the synthesized nanocomposites was evaluated using XRD and TEM, from these results, it was confirmed that 0.5 wt% loaded PET/MgAl LDH‐SAS and PET/CL120‐DT nanocomposites have flocculated and intercalated morphologies, respectively. Thermomechanical analyses were performed by thermogravimetric analysis, dynamic mechanical analysis, and differential scanning calorimetry, respectively. Moreover, the water vapor transmission rate (WVTR) values of a pure PET, PET/CL120‐DT 0.5 wt%, and PET/MgAl LDH‐SAS 0.5 wt% nanocomposites were found to be 49, 45, and 46 g·m^?2·day^?1, respectively. Furthermore, the gas barrier properties of PET composite films containing various amounts of inorganic nanoparticles were investigated using Gas permeability analysis (GPA).     

Effect of annealing on the viscoelastic and viscoplastic responses of low‐density polyethylene

Two series of tensile tests with constant crosshead speeds (ranging from 5 to 200 mm/min) and tensile relaxation tests (at strains from 0.03 to 0.09) were performed on low‐density polyethylene in the subyield region of deformations at room temperature. Mechanical tests were carried out on nonannealed specimens and on samples annealed for 24 h at the temperatures T = 50, 60, 70, 80, and 100 °C. Constitutive equations were derived for the time‐dependent response of semicrystalline polymers at isothermal deformations with small strains. A polymer is treated as an equivalent heterogeneous network of chains bridged by temporary junctions (entanglements, physical crosslinks, and lamellar blocks). The network is thought of as an ensemble of mesoregions linked with each other. The viscoelastic behavior of a polymer is modeled as a thermally induced rearrangement of strands (separation of active strands from temporary junctions and merging of dangling strands with the network). The viscoplastic response reflects sliding of junctions in the network with respect to their reference positions driven by macrostrains. Stress‐strain relations involve five material constants that were found by fitting the observations. Fair agreement was demonstrated between the experimental data and the results of numerical simulation. This study focuses on the effects of strain rate and annealing temperature on the adjustable parameters in the constitutive equations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1638–1655, 2003     

Characterization of an unsaturated low‐density polyethylene

This study concerns a new group of low‐density polyethylenes (LDPEs)—unsaturated LDPE. The new LDPE is a copolymer between ethylene and 1,9‐decadiene and was polymerized in a commerical high‐pressure tubular reactor. The diene copolymerized with one double bond, leaving the other unreacted as a pendant side group. This yielded a copolymer containing a higher number of vinyl groups than ordinary LDPE. Fractionation of the copolymer and determination of the number of unsaturated structures in the different fractions by Fourier transform infrared spectroscopy revealed that the diene is homogeneously incorporated along the molar‐mass distribution curve. It is also possible to obtain copolymers with a varying vinyl content, without drastic changes in molar mass or molar‐mass distribution, by a controlled addition of 1,9‐decadiene to the reactor. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2974–2984, 2003     

Conversion of low density polyethylene foams into auxetic metamaterials

Cellular polymers, such as polyethylene foams, are commonly used in the packaging industry. These materials have short service life and generate a high volume of waste after use. In order to valorize this waste and produce added-value applications, it is proposed to convert these materials into highly efficient energy absorption structures. This was done by modifying the original cellular morphology of the foams (spheroidal or polygonal) into a re-entrant structure to produce auxetic materials. This work presents an optimized process combining mechanical compression and solvent vapor evaporation-condensation leading to low density foams (77–200 kg/m³) having negative Poisson's ratios (NPR). Three series of recycled low density polyethylene (LDPE) foams with an initial density of 16, 21, and 36 kg/m³ were used to optimize the processing conditions in terms of treatment temperature, time, and pressure. From all the samples prepared, a minimum Poisson's ratio of −3.5 was obtained. To further characterize the samples, the final foam structure was analyzed to relate with mechanical properties and compare with conventional foams having positive Poisson's ratios. The results are discussed using tensile properties and energy dissipation which were shown to be highly improved for auxetic foams. Overall, the resulting foams can be used in several applications such as sport and military protection equipment.     

Effect of stretching on structure and properties of polyethylene hollow fiber membranes made by melt‐spinning and stretching process

Microporous polyethylene (PE) hollow fiber membrane was prepared by the melt‐spinning and stretching (MS‐S) method. The effect of stretching on the structure and properties of the membrane was investigated by water contact angle measurement, field emission scanning electron microscopy (FESEM), mercury porosimetry, and N₂ permeation. The tensile experiment was used to study the hard elasticity and the mechanical properties of annealed PE fibers. During the stretching process, the stretching temperature, rate, and ratio have great effects on the morphology, crystal structure, pore structure, and N₂ permeation of the membrane. Experimental results showed that N₂ permeation and porosity of the membrane increased with the increase in stretching temperature, rate, and ratio. The pore size decreased with increase in the stretching rate and increased with the stretching ratio. The pore size distribution was also affected by the stretching process, and was investigated in detail. Copyright © 2008 John Wiley & Sons, Ltd.     

One‐step synthesis of polysiloxane graft polyethylene mimic: Non‐expensive compatibilizer for polyethylene/polysiloxane blend

Polysiloxane/polyolefin copolymers have drawn much attention recently and emerged as a new group of functional polyolefin since they possess distinctive properties and find great potential applications in many areas (eg, compatibilizer, processing aid and surface modifier). However, traditional routes to synthesize polysiloxane/polyolefin copolymers generally require multi‐step labor‐consuming procedures. Herein, we report a novel one‐step synthesis of polydimethylsiloxane graft polyethylene (PDMS‐g‐PE) mimics. It was found that PDMS‐g‐PE mimics, namely vinylmethylsiloxane‐dimethylsiloxane‐(C30‐45 alkyl)methylsiloxane copolymers (short for VD‐AMS), could be formed via a one‐step synthetic procedure based on the siloxane equilibrium process between silanol‐terminated vinylmethylsiloxane‐methylsiloxane copolymer and (C30‐45 alkyl)methylsilicone. The chemical structures of VD‐AMS were characterized unambiguously using Fourier transform infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimetry. The correlation between reaction conditions and the structural parameters of VD‐AMS was established. Based on our experimental results, a plausible mechanism for the synthesis of VD‐AMS was proposed. Scanning electron microscopy micrographs showed that VD‐AMS could function as an efficient compatibilizer for immiscible PE/silicone blend. Given that the precursors of VD‐AMS are commercially available with low prices and that VD‐AMS can be easily synthesized under mild conditions, we believe VD‐AMS can represent as a competitive potential compatibilizer due to its relatively low cost.     

Surface modification of ultrahigh‐molecular‐weight polyethylene fibers

To prevent the loss of fiber strength, ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers were treated with an ultraviolet radiation technique combined with a corona‐discharge treatment. The physical and chemical changes in the fiber surface were examined with scanning electron microscopy and Fourier transform infrared/attenuated total reflectance. The gel contents of the fibers were measured by a standard device. The mechanical properties of the treated fibers and the interfacial adhesion properties of UHMWPE‐fiber‐reinforced vinyl ester resin composites were investigated with tensile testing. After 20 min or so of ultraviolet radiation based on 6‐kW corona treatment, the T‐peel strength of the treated UHMWPE‐fiber composite was one to two times greater than that of the as‐received UHMWPE‐fiber composite, whereas the tensile strength of the treated UHMWPE fibers was still up to 3.5 GPa. The integrated mechanical properties of the treated UHMWPE fibers were also optimum. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 463–472, 2004     

Synthesis of ultra‐low‐molecular‐weight polyethylene wax using a bulky Ti(IV) aryloxide–alkyl aluminum catalytic system

Complexes of titanium(IV) with bulky phenolic ligands such as 2‐tert‐butyl‐4 methylphenol, 2, 4‐di‐tert‐butyl phenol and 3,5‐di‐tert‐butyl phenol were prepared and characterized. These catalyst precursors, formulated as [Ti(OPh*)_n(OPrⁱ)_4?n] (OPh* = substituted phenol), were found to be active in polymerization of ethylene at higher temperatures in combination with ethylaluminum sesquichloride (Et₃Al₂Cl₃) as co‐catalyst. It was observed that the reaction temperature and ethylene pressure had a pronounced effect on polymerization and the molecular weight of polyethylene obtained. In addition, this catalytic system predominantly produced linear, crystalline ultra‐low‐molecular‐weight polyethylenes narrow dispersities. The polyethylene waxes obtained with this catalytic system exhibit unique properties that have potential applications in surface coating and adhesive formulations. Copyright © 2007 John Wiley & Sons, Ltd.     

Linear low‐density polyethylene nanocomposites by in situ polymerization using a zirconium‐nickel tandem catalyst system

A series of linear low‐density polyethylene (LLDPE) nanocomposites containing different types of nanofiller (TiO₂, MWCNT, expanded graphite, and boehmite) were prepared by in situ polymerization using a tandem catalyst system composed of {Tp^Ms}NiCl ( 1 ) and Cp₂ZrCl₂ ( 2 ), and analyzed by differential scanning calorimetry, dynamic mechanical analysis (DMA), and transmission electron microscopy (TEM). Based on these analyses, the filler content varied from 1.30 to 1.80 wt %. The melting temperatures and degree of crystallinity of the LLDPE nanocomposites were comparable to those of neat LLDPE. The presence of MWCNT as well as boehmite nucleated the LLDPE crystallization, as indicated by the increased crystallization temperature. The DMA results showed that the presence of TiO₂, EG, and CAM 9080 in the LLDPE matrix yielded nanocomposites with relatively inferior mechanical properties compared to neat LLDPE, suggesting heterogeneous distribution of these nanofillers into the polymer matrix and/or the formation of nanoparticle aggregates, which was confirmed by TEM. However, substantial improvement in the storage modulus was achieved by increasing the sonication time. The highest storage modulus was obtained using MWCNT (1.30 wt %). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3506–3512