Tear anisotropy in films blown from polyethylenes of different macromolecular architectures

Blown films of different types of polyethylenes, such as branched low‐density polyethylene (LDPE) and linear high‐density polyethylene (HDPE), are well known to tear easily along particular directions: along the film bubble's transverse direction for LDPE and along the machine direction (MD) for HDPE. Depending on the resin characteristics and processing conditions, different structures can form within the film; it is therefore difficult to separate the effects of the crystal structure and orientation on the film tear behavior from the effects of the macromolecular architecture, such as the molecular weight distribution and long‐chain branching. Here we examine LDPE, HDPE, and linear low‐density polyethylene (LLDPE) blown films with similar crystal orientations, as verified by through‐film X‐ray scattering measurements. With these common orientations, LDPE and HDPE films still follow the usual preferred tear directions, whereas LLDPE tears isotropically despite an oriented crystal structure. These differences are attributed to the number densities of the tie molecules, especially along MD, which are considerably greater for linear‐architecture polymers with a substantial fraction of long chains, capable of significant extension in flow. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 413–420, 2005     

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     

A real-time WAXS and SAXS study of the structural evolution of LLDPE bubble

The structural evolution during the linear low-density polyethylene (LLDPE) film blowing has been studied with a combination of home-made blown film apparatus and in situ WAXS and SAXS measurements. Analyzing the evolution of orientation parameters and crystallinity of the bubble shows that the blown film process can be divided into four regions. Distinctly different features of LLDPE bubble are observed in first three regions: (a) lower orientation parameters during the blown film process, (b) higher crystallinity is required to form a deformable crystalline crosslinked network, and (c) the weaker stretching effect and the difficulty of reaching equilibrium when the crystal network deforms. These results should provide a basis for understanding the poor blown film stability of LLDPE. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1404–1412     

Structure of Composite Films Containing Polyaniline Studied by DSC

A structural study of conductive composite films consisting of ethylene-co-vinylacetate (EVA) copolymer, polyaniline (PANI) and dodecylbenzenesulfonic acid (DBSA), a part of which being complexed with PANI, was performed by using differential scanning calorimetry (DSC) and presented for the first time. An additional crystalline phase is formed during the film formation by thickening EVA chain-folded lamellae with participation of‘free’ DBSA molecules at lower net PANI content (up to 5 mass%) and of both ‘free’ and complexed DBSA molecules (up to 7.5 mass%). At higher PANI content PANI-DBSA complex starts to form its own crystals and at 17.5 mass% of PANI mixed crystals of EVA with ‘free’ DBSA alkyl chains are preferably formed. It is also found that the Fox' equation correlating the glass transition temperature of a miscible blend system with its composition can be actually used in estimating the miscibility of EVA/PANI blends no matter the presence of DBSA. This revised version was published online in August 2006 with corrections to the Cover Date.     

利用~1H-NMR研究HDPE/PET/EVA共混体系的酯交换反应

本文在选用EVA作为HDPE/PET共混体系增容剂的基础上 ,通过双螺杆反应挤出熔融加工过程 ,促使EVA侧基上的酯基官能团与PET组分主链上的酯基在适当催化剂———有机金属化合物存在的条件下发生酯交换反应 .1H NMR结果表明 ,酯交换反应的产生在共混体系界面原位形成接枝或交联的PET EVA共聚物 ,且主要是以生成接枝共聚物的反应为主 .     

Preparation and Properties of Polyether Pentaerythritol Mono‐maleate grafted Linear Low Density Polyethylene by Reactive Extrusion

A reactive type nonionic surfactant, polyether pentaerythritol mono‐maleate (PPMM) was synthesized in our laboratory. PPMM was adopted as a functionalizing monomer and grafted onto linear low density polyethylene (LLDPE) with a melt reactive extrusion procedure. FT‐IR was used to characterize the formation of grafting copolymer and evaluate their degree of grafting. The effects of monomer concentration, reaction temperature and screw run speed on the degree of grafting were studied systematically. Isothermal crystallization kinetics of LLDPE and LLDPE‐g‐PPMM samples was carried out using DSC. Crystallization rates of grafted LLDPE were faster than that of plain LLDPE at the same crystallization temperature. The tensile properties and light transmission of blown films were determined. Comparing with neat LLDPE film, no obvious changes could be found for the tensile strength, elongation at break and right angle tearing strength of LLDPE‐g‐PPMM film. The wettability is expressed by the water contact angle. With an increasing percentage of PPMM, the contact angles of water on film surface of LLDPE‐g‐PPMM decrease monotonically. The acceleration dripping property of film samples was investigated. The dripping duration of LLDPE‐g‐PPMM film and commercial anti‐fog dripping film at 60°C were 76 days and 17 days, respectively.     

Structure formation in polymer blends as a result of phase separation and deformation processes

Polymeric blends, which are materials consisting of two or more polymers, are gaining in practical importance and scientific interest. The properties of these materials are greatly affected by their state of miscibility. This paper reviews selected thermodynamic and rheological considerations regarding the phase behavior and the morphological control of polymer blends. Major emphasis is placed on the phase behavior of poly-blends comprising random copolymers. - The majority of polymer blends are microheterogeneous systems. There is consequently, a great need for control of the phase morphology during processing of immiscible polymers to achieve the desired property combinations. The key to this are both the microrheology of the phases and the macrorheology of the dispersion itself. In a qualitative way, one can establish that the ratio of the viscosities and the difference in the elasticities of the components determine sizes and shapes, respectively, of the phases indicating that the variety of morphologies observed in polymer-polymer systems subjected to shearing has to be attributed to the viscoelasticity of each component. Furthermore, particular compositions are associated with changes in the morphology. This fact supports the particular compositions as an inherent feature of the melt rheology of polyblends.     

Morphological,rheological, crystalline and mechanical properties of ethylene-vinyl acetate copolymer/linear low-density polyethylene/amphiphilic graphene oxide nanocomposites

Chemical modification of graphene oxide has become a popular method for imparting unique properties to extend its application. Here, we show a simple way to synthesize amphiphilic graphene oxide (AGO) by grafting quaternary ammonium salt onto GO sheets. The AGO sheets not only showed high thermal stability and good dispersion in many polar and non-polar solvents in comparison to GO sheets but also the chemical modification maintained the two-dimensional structure. As a result, the AGO sheets improve the interfacial interaction between ethylene-vinyl acetate copolymer (EVA) and linear low-density polyethylene (LLDPE). Because of the large size of AGO, the location of AGO is very dependent on the mixing strategy. The AGO was dispersed in the EVA phase when AGO was mixed first with EVA and then with LLDPE, whereas it was confined in the LLDPE phase when AGO was mixed first with LLDPE and then with EVA. AGO sheets were found at the interface of LLDPE and EVA when AGO, EVA, and LLDPE were mixed together, suggesting that AGO has a high interfacial interaction with both LLDPE and EVA. These high interfacial interactions lead to high tensile strength, Young's modulus, complex viscosity and crystallization temperature in comparison to the EVA/LLDPE blends without AGO sheets.     

A universal blown film apparatus for <Emphasis Type="Italic">in situ</Emphasis> X-ray measurements

A setup of blown film machine combined with in situ synchrotron radiation X-ray diffraction measurements and infrared temperature testing is reported to study the structure evolution of polymers during film blowing. Two homemade auto-lifters are constructed and placed under the blown machine at each end of the beamline platform which move up and down with a speed of 0.05 mm/s bearing the 200 kg weight machine. Therefore, structure development and temperature changes as a function of position on the film bubble can be obtained. The blown film machine is customized to be conveniently installed with precise servo motors and can adjust the processing parameters in a wide range. Meanwhile, the air ring has been redesigned in order to track the structure information of the film bubble immediately after the melt being extruded out from the die exit. Polyethylene (PE) is selected as a model system to verify the feasibility of the apparatus and the in situ experimental techniques. Combining structure information provided by the WAXD and SAXS and the actual temperature obtained from the infrared probe, a full roadmap of structure development during film blowing is constructed and it is helpful to explore the molecular mechanism of structure evolution behind the film blowing processing, which is expected to lead to a better understanding of the physics in polymer processing.     

Thermal,rheological, morphological and mechanical properties of high density polyethylene/ethylene vinyl acetate copolymer (HDPE/EVA) blends

Thermal, rheological, morphological and mechanical properties of binary HDPE and EVA blends were studied. The results of rheological studies showed that for given HDPE and EVA, the interfacial interaction in HDPE-rich blends is higher than EVA-rich blends. Using three different rheological criterions, the phase inversion composition was predicted to be in 30 wt% of the EVA phase. This showed good agreement with morphological studies. The tensile strength for HDPE-rich blends showed positive deviation from mixing rule, whereas the EVA-rich blends played negative deviation. These results were in a good agreement with the results of viscoelastic behavior of the blends. The thermal analysis revealed that high co-crystallizaiton in 90/10 composition, which increased the tensile strength and decreased the elongation at break in this composition. Furthermore, the results of thermal behavior of the blends indicated that the melting temperatures of HDPE decrease due to the dilution effect of EVA on HDPE.     

The rheological behavior of ethylene vinyl acetate copolymer/rectorite nanocomposites during the melt extrusion process

To optimize the preparation process for ethylene vinyl acetate (EVA)/rectorite nanocomposites during the melt extrusion, the effect of rectorite on the rheological property of molten polymer has been explored in this paper. The dispersion of rectorite in EVA was probed by X‐ray diffraction, and the rheological behaviors of EVA copolymer and EVA/rectorite nanocomposites during the extrusion process were investigated by means of HAAKE minilab. The positron results reveal that introducing the rectorite in EVA matrix increases the interfaces in composites. And the rheological results indicate that the viscosity of EVA and EVA/rectorite nanocomposites in the molten state was influenced by the processing temperature, processing time and shearing rate. For all the samples, the viscosity increases with increasing the shear rate, and decreases with increasing extrusion temperature. Moreover, compared with the pure EVA, the EVA/rectorite nanocomposite presents a lower viscosity at the same processing condition. Copyright © 2016 John Wiley & Sons, Ltd.     

Nonisothermal crystallisation, melting behavior and wide angle X-ray scattering investigations on linear low density polyethylene (LLDPE)/ethylene vinyl acetate (EVA) blends: effects of compatibilisation and dynamic crosslinking

Crystallisation studies on LLDPE/EVA blends and the individual components were performed with wide angle X-ray scattering (WAXS) technique and differential scanning calorimetry (DSC) DSC was used to characterise the quiescent crystallisation behavior. The heat of fusion and crystallinity of the blends were reduced by the addition of EVA. The experimental and theoretical values of crystallinity of the blends were found to be mutually agreeing. Crystallisation of LLDPE remains impeded to some extent due to the presence of amorphous EVA. Compatibilisation does not affect crystallinity whereas crosslinking decreases crystallinity. Crosslinking and compatibilisation make no significant change in the melting temperature of the blends. X-ray diffraction studies were carried out on un-crosslinked and crosslinked LLDPE/EVA blends with a view to study the effect of blend composition and crosslinking on crystallinity and lattice distance. Studies revealed that LLDPE and EVA have orthorhombic unit cell. Blending with EVA did not affect the crystalline structure of LLDPE, but the crystallinity decreases with EVA content. At low concentrations of EVA the lattice parameters remain unchanged. Above 30% EVA content however, a linear increase has been observed. Dicumyl peroxide (DCP) crosslinked samples show considerable shift of (1 1 0), (2 0 0) and (0 2 0) crystalline peaks towards lower 2θ values indicating an increase of unit cell parameters of the orthorhombic unit cell of polyethylene. At lower EVA-concentrations (<50%) the crystalline structure remains unchanged. For EVA-contents of more than 70% however, increasing DCP-content reduces the crystallinity of the blends and increases the lattice distance. This indicates that DCP-crosslinking is more effective in EVA phase than in the LLDPE phase.     

A Universal Blown Film Apparatus for in Situ X-ray Measurements

A setup of blown film machine combined with in situ synchrotron radiation X-ray diffraction measurements and infrared temperature testing is reported to study the structure evolution of polymers during film blowing.Two homemade auto-lifters are constructed and placed under the blown machine at each end of the beamline platform which move up and down with a speed of 0.05 mm/s bearing the 200 kg weight machine.Therefore,structure development and temperature changes as a function of position on the film bubble can be obtained.The blown film machine is customized to be conveniently installed with precise servo motors and can adjust the processing parameters in a wide range.Meanwhile,the air ring has been redesigned in order to track the structure information of the film bubble immediately after the melt being extruded out from the die exit.Polyethylene (PE) is selected as a model system to verify the feasibility of the apparatus and the in situ experimental techniques.Combining structure information provided by the WAXD and SAXS and the actual temperature obtained from the infrared probe,a full roadmap of structure development during film blowing is constructed and it is helpful to explore the molecular mechanism of structure evolution behind the film blowing processing,which is expected to lead to a better understanding of the physics in polymer processing.     

The use of thermoplastic elastomers as polymer processing aids in processing of linear low density polyethylene

Commercially available thermoplastic elastomers based on block copolymers of diisocyanates and polyols and based on silicones have been reported by Kulikov et al. (2004 and 2006) to delay sharkskin in extrusion of Linear Low Density Polyethylene. In this work thermoplastic elastomers have been used as polymer processing additives in blown film extrusion of Linear Low Density Polyethylene. When a thermoplastic elastomer is added in small amounts to Linear Low Density Polyethylene it deposits at the die surface during extrusion and may postpone the onset of sharkskin enabling up to 20 times higher rate of extrusion. Many thermoplastic elastomers are certified for body and food contacts and could be a cost-effective substitution of fluorinated polymers in processing of Linear Low Density Polyethylene by extrusion. Oscillating and capillar rheometry have been used to reveal the mode of action of the additives. Results of capillar rheometry showed a decrease of apparent viscosity of the polymer melt when additive was added. Therefore Mooney method (Mooney, 1931) was applied to prove occurring slip inside of the die. Substantial delay of sharkskin was achieved also in conditions without slip of molten polyethylene inside the die by adding thermoplastic elastomer based on urethanes. Oscillating rheometry has been used to characterize elasticity of the materials. It could be shown that efficiency to delay sharkskin depends on elasticity of the specific thermoplastic elastomer at processing temperature. Surface tension of the solid materials was used to estimate the mutual affinity of the materials. Therefore a theoretical model of Rathod and Hatzikiriakos (2004) was used to evaluate the data. Finally a classification of polymer processing aids into “slip inducers” and “flow enhancers” by their mode of action was done. Ability of novel processing aids to postpone sharkskin was shown in blown film extrusion. Applicability of polymer processing aids in injection moulding could be proved by use of a mould with spiral cavity.     

AN EVA/UNMODIFIED NANO-MAGNESIUM HYDROXIDE/SILICONE RUBBER NANOCOMPOSITE WITH SYNERGISTIC FLAME RETARDANCY

A novel EVA/unmodified nano-magnesium hydroxide(NMH)/silicone rubber ternary nanocomposite was prepared by using a special compound flame retardant of NMH and silicone rubber(CFR).The flammability of the ternary composite was studied by cone calorimeter test(CCT).Synergistic effect on flame retardancy was found between silicone rubber and NMH.EVA/CFR ternary nanocomposite showed the lowest peak heat release rate(PHRR)and mass loss rate (MLR)among the samples of virgin EVA,EVA composites.The synergistic flame retardancy of silicone rubber and NMH in EVA system is attributed to the enhanced char layers in the condensed phase that prevents the heat and mass transfer in the fire.     

Annealing of Polypropylene/Polyethylene Blends Near to the Melting Points in TMDSC

Annealing experiments have been carried out just below the melting temperature of both polyethylene (LLDPE) and polypropylene (PP) and their blends. The total melting enthalpy measured after the annealing cycle was greater by 10-15% with respect to the value having been measured before it. During the annealing period the heat capacity decreases to a lower value within the first 2-3 min. Heat capacities of PP (either in pure form or in the blends) measured during the heating cycle following the annealing cycle have the same value as during the cooling section. The heat capacities of the LLDPE in the heating cycle following the annealing were those of the preceding heating cycle. The total heat flows in the cooling section following the annealing cycle were greater than those in another cooling cycle at the same temperatures indicating that the crystallisation takes place during the cooling rather than during the annealing periods. The presence of LLDPE decreases the crystallisation temperature of PP. The presence of SEBS in the blend results in a greater crystallisation temperature than that of pure PP. The crystallisation temperature of LLDPE increases with increasing levels of PP. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of the molecular architecture of low‐density polyethylene on the texture and mechanical properties of blown films

Three types of low‐density polyethylene materials were investigated with respect to the influence of the molecular architecture on the mechanical and use properties of blown films. The materials were a branched polyethylene synthesized by free‐radical polymerization under high‐pressure (HP‐LDPE), a linear ethylene–hexene copolymer (ZN‐LLDPE) produced by low‐pressure Ziegler–Natta catalysis, and an ethylene–hexene copolymer (M‐LLDPE) from metallocene catalysis. The extrusion and blowing conditions were identical for the three materials, with a take‐up ratio of 12 and a blow‐up ratio of 2.5. The blown films displayed a decreasing puncture resistance in the order M‐LLDPE, ZN‐LLDPE, and HP‐LDPE. In parallel, the tear resistance of the films became increasingly unbalanced in the same order of the polymers. The morphological study showed an increased anisotropy of the films in the same polymer order, the crystalline lamellae being increasingly oriented normal to the take‐up direction. This texturing caused a detrimental effect on the mechanical properties of the films, notably increasing the capacity for crack propagation. The phenomenon was ascribed to the kinetics of chain relaxation in the melt that governed the ability of the chains to recover an isotropic state from the flow‐induced stretching before crystallization. The puncture resistance was examined in terms of both texture and strain‐hardening capabilities. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 327–340, 2003     

Miscibility behavior of ethylene/vinyl acetate and C5 petroleum resin by FTIR imaging.

FTIR microscopic imaging was used to investigate the miscibility behavior of ethylene/vinyl acetate copolymer (EVA) and C5 petroleum resin. Images with an area of 500 x 500 microm(2) were collected in the reflection mode. The miscibility was characterized by probing the spatial distribution of the carbonyl group (C=O) of EVA in the whole images. It was found that a 1:1 hot-melt mixture of EVA and C5 resin showed a good miscibility behavior. For two different EVA copolymers, one with 18% vinyl acetate (VAc) content showed a better miscibility behavior than that with 28% VAc content. Our results demonstrated that this method allowed a direct, convenient and nondestructive visualization. This developed technique promises to become a powerful tool for studying the miscibility behavior of composite materials.     

Effects of atmospheric plasma treatment on the interfacial characteristics of ethylene-vinyl acetate/polyurethane composites

The surface characteristics of ethylene-vinyl acetate (EVA) were modified by argon, air, and oxygen plasma at atmospheric pressure. The surface energies of the EVA were evaluated by contact angles according to a sessile-drop method and adhesion energy (G(IC)) was estimated by a 180 degrees peel test with polyurethane (PU). After the plasma treatments, the surface free energies (or specific polar component) of the EVA increased about five times compared to that of virgin EVA. The adhesion between the EVA and the PU is significantly improved by the plasma treatment. Especially, Ar/air/O(2) plasma treatment increases G(IC) of EVA/PU up to about 600% compared to that of the sample using virgin EVA.     

Preparation,Characterization and Properties of Reactive Type Dripping Agent Tween 60-IAH and Their Grafting Copolymer With Linear Low Density Polyethylene

A kind of reactive type dripping agent (Tween 60-IAH) was synthesized with polyethylene glycol sorbitan monostearate (Tween 60) and itaconic anhydride (IAH) as main starting materials. The chemical structure of Tween 60-IAH was characterized by means of Fourier transform infrared (FT-IR) spectroscopy. The effect of reaction time on conversion of Tween 60-IAH was studied. The results of thermogravimetric analysis (TGA) measurement demonstrated that Tween 60-IAH exhibited a better thermal stability than Tween 60. Grafting copolymer of linear low density polyethylene (LLDPE) with Tween 60-IAH was prepared in twin-screw extruder. Thermal and rheological properties of grafted LLDPE samples were investigated with differential scanning calorimetry (DSC) and rotational rheometer. Crystallization temperatures of grafted LLDPE were higher than that of LLDPE. Complex viscosities of grafted LLDPE at high shear rates were lower than that of LLDPE. The dripping properties of film samples were investigated at 60°C.