Toughening effect of maleic anhydride grafted linear low density polyethylene on linear low density polyethylene

The blend of linear low density polyethylene (LLDPE) and maleic-anhydride grafted LLDPE with the grafting degree of 1.3% and the gel content of 27.0% (designated as LLDPE/MA-PE) was melt-compounded. Their thermal, rheological, and mechanical properties were studied. The crystallization temperature and crystallization rate of LLDPE/MA-PE blends increase due to the nucleation of MA-PE, their crystallinity is between those of LLDPE and MA-PE due to the balance between the nucleation of MA-PE and simultaneously produced more defects. The addition of MA-PE increases the apparent viscosity of blend melts, but the shear-sensitivity of blends provides them with melting processing. Interestingly, the lamellar crystallites induced by MA-PE decrease the tensile yielding strength of LLDPE/MA-PE blends. During the impact fracture, the formation of oriented crystalline lamellae parallel to the crack front and perpendicular to the crack flank, leads to the deformation and microstriations in LLDPE/MA-PE blends. Subsequently, toughness of LLDPE/MA-PE blends is improved.     

微纤化纤维素/线性低密度聚乙烯复合材料

微纤化纤维素（MFC）具有优良的力学性能,常被用作增强体制备复合材料,但MFC容易团聚影响其增强能力。本研究对MFC进行低温冷冻干燥处理（FDMFC）,用微型锥形双螺杆挤出机将FDMFC与线性低密度聚乙烯（LLDPE）熔融复合,并用热压-冷压的方式制备FDMFC/LLDPE复合材料,对其力学性能、动态热力学性能（DMA）、热分解过程及冷冻干燥处理的FDMFC在LLDPE基体中的分散状态进行了测试。结果表明:相对于未冷冻干燥处理的MFC,FDMFC在LLDPE基体中的分散性得到明显改善,添加一定量的FDMFC可有效提高FDMFC/LLDPE复合材料的力学性能。当FDMFC的添加量为10wt%时,相较于纯LLDPE,FDMFC/LLDPE复合材料的拉伸强度提高了60.3%,杨氏模量提高了161.9%。DMA测试结果表明,随着FDMFC含量的增加,FDMFC/LLDPE复合材料的储能模量和损耗模量都有所提高。热重分析结果表明,FDMFC的加入提高了FDMFC/LLDPE复合材料的热解温度,最大热解温度提高了14℃。      

Amorphous carbon fibres from linear low density polyethylene

Carbon fibres with good mechanical properties have been produced from linear low density polyethylene (LLDPE). The melt-spun LLDPE fibres were made infusible by treatment with chlorosulphonic acid. The cross-linked fibres were pyrolysed at temperatures between 600 and 1100 °C under tension, in a nitrogen atmosphere, within 5 min. Carbon fibres prepared at 900 °C had a tensile strength of 1.15 GPa and a Young's modulus of 60 GPa. The elongation at break was extremely high, up to 3%. The carbon yield of the process was 72 to 75%.     

枣核/低密度聚乙烯复合材料的力学性能

为充分利用红枣精深加工产生的废弃物,以枣核(JP)和低密度聚乙烯(LLDPE)为主要材料,采用注塑成型法制备JP/LLDPE复合材料,并对其静态力学性能(拉伸、弯曲和冲击)和动态力学性能(动态黏弹性、蠕变行为和应力松弛行为)进行系统测试分析.静态力学性能分析表明,随JP含量的增加,JP/LLDPE复合材料的拉伸强度和冲...     

微注射成型高密度聚乙烯-线性低密度聚乙烯共混物的微结构及力学性能

为提高线性低密度聚乙烯（LLDPE）的拉伸强度和模量,扩大其应用领域,将三种不同相对分子质量的高密度聚乙烯（HDPE）分别与LLDPE共混,通过微注射成型技术制备HDPE-LLDPE制品。综合利用DSC、广角X射线衍射（WAXD）、小角X射线散射（SAXS）和拉伸性能测试研究了共混物在微注射成型过程中的结构演化及力学性能。拉伸测试结果表明,与纯LLDPE相比,HDPE-LLDPE的拉伸强度和模量随HDPE分子量的增加而增加。微结构分析结果显示,随HDPE分子量的增加,HDPE-LLDPE制品的分子链和片晶取向度增大、结晶度增加,且制品内形成了较多取向的Shish-Kebab晶体结构。通过分析微结构的表征结果,解释了HDPE-LLDPE的拉伸强度和模量显著提高的原因。     

Thermal effects in high density polyethylene and low density polyethylene at high hydrostatic pressures

The temperature changes as a result of rapid hydrostatic pressure applications are reported for high density polyethylene (HDPE) and low density polyethylene (LDPE) in the reference temperature range from 298 to 423 K and in the pressure range from 13.8 to 200 MN m^–2. The adiabatic temperature changes were found to be a function of pressure and temperature. A curve fitting analysis showed that the empirical curve (/P) =ab(P)^b–1 described the experimental thermoelastic coefficients obtained from the experiments. The data were analyzed by determining the predicted thermoelastic coefficients derived from the Thomson equation (/P) = T ₀/C _p. The experimental and predicted Grüneisen parameter _T were also determined.     

Composites of linear low density polyethylene and short sisal fibres: The effects of peroxide treatment

Influence of sisal fibre content and different concentrations of dicumyl peroxide (DCP) on the thermal, mechanical and viscoelastic properties of short sisal fibre—linear low-density polyethylene (LLDPE) composites was investigated. Significant improvement of tensile strength was found after peroxide induced grafting between fibres and PE matrix. The stress relaxation measurements also suggest better stability upon prolonged loading of the samples prepared with 1% of DCP. It was shown, on the other hand, that higher DCP concentrations could have detrimental effects on the PE matrix, especially at low fibre contents.     

On the use of nanoscale indentation with the AFM in the identification of phases in blends of linear low density polyethylene and high density polyethylene

The microstructures generated by blends of linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) following isothermal crystallization from the melt have been studied using several techniques. The traditional methods of electron microscopy, wide angle X-ray scattering, and differential scanning calorimetry were used to examine the superstructures, lattice spacings, and thermal properties, respectively. In addition, nanoindentation of specific moieties within the microstructure was performed using the atomic force microscope (AFM). The indentation measurements were used to generate values for the relative elastic moduli of the crystalline features and to identify phases within the superstructures. The AFM results were compared to results obtained from the aforementioned techniques and to microhardness measurements.     

Mechanical and structural studies of low density polyethylene

During uniaxial orientation of low density polyethylene (LDPE) at 90 to 95°C some unusual structural changes occur, as revealed by wide and low angle X-ray diffraction. Quantitative measurements of diffracted intensity distributions have been made. At low draw ratios a novel 6-point low angle pattern appears which persists to extensions of over 300%. Cone distributions are present in all the crystal axis orientations, and these are superimposed on transverse components to give complex wide angle diffracted intensity profiles. A spherulite deformation model is proposed to explain these observations. At high draw ratios uniaxial crystal alignment obtains, but we find that the lamellar orientations differ between specimens annealed after drawing at room temperature and those drawn directly at the higher temperature. The implications of this observation are considered.     

Mechanical and structural studies of low density polyethylene

This paper is one of a series concerned with the complete characterisation of the creep behaviour of oriented polymers, the correlation of creep behaviour with other mechanical properties and the interpretation of such data in the light of present structural knowledge. Sheets of oriented low-density polyethylene were prepared from initially isotropic sheets by cold-drawing, cold-drawing followed by heat-treatment at 55° C, drawing at a temperature of 55° C and hot-drawing at temperatures in the range 90 to 100° C. At each draw ratio, specimens were cut at angles of 0°, 45° and 90° to the draw direction. For each specimen, the variation of longitudinal and lateral strain with time, during uniaxial tensile creep at 20° C, was measured simultaneously by direct extensometer methods, for a wide range of applied stresses. All the materials exhibited complex anisotropic non-linear viscoelastic behaviour. The methods of presenting such data are discussed and the results are presented in some detail. Many similarities in the creep behaviour of the cold- and hot-drawn materials are noted. However, marked differences are apparent in the non-linearity and creep rate of the 45° specimens from these two materials at high draw ratio. These, and other effects found at high draw ratio, are discussed with reference to the structural studies reported in part 1. At low draw ratio, it is shown that the anomalous behaviour of the modulus in the draw direction, reported previously for cold-drawn material, may also be found in the hot-drawn material, although at a different creep time. On the basis of obvious differences in wide-angle X-ray patterns other workers had previously predicted that the anomalous mechanical behaviour of cold-drawn LDPE was probably unique. The anomalous behaviour of the hot-drawn material is also explained in terms of the structures discussed in part 1.     

The preparation of carbon nanotube/linear low density polyethylene composites by a water-crosslinking reaction

A novel method to prepare the carbon nanotube (CNT)/linear low density polyethylene (LLDPE) composite is demonstrated. The combination of free radical reaction and water-crosslinking reaction to prepare the CNT/LLDPE composite was characterized by Raman and FT-IR. Mechanical properties and thermal stability of the composite were significantly improved after silane modification and water-crosslinking reaction.     

Sorption and diffusion of aromatic solvents through linear low density polyethylene–ethylene vinyl acetate blend membranes

An investigation has been made for understanding the transport behaviour of organic solvents through linear low-density polyethylene (LLDPE)/ethylene vinyl acetate (EVA) blend membranes with special reference to the effects of blend ratio, concentration of cross-linking agent, penetrant size and temperature. Attempts have been made to relate the transport parameter with the morphology of the blend. The various transport parameters such as diffusion coefficient (D), permeation coefficient (P) and sorption coefficients (S) were evaluated at different diffusion conditions. The results were compared with theoretical predictions and found that the diffusion process follows anomolous type behaviour. The blends show dispersed/matrix and co-continuous phase morphologies depending on the composition. Dynamic vulcanization leads to fine and uniform distribution of the dispersed domains with a stable morphology. Among the blends E₇₀ sample shows the maximum solvent uptake and E₃₀ the minimum. The solvent uptake of blend varies with concentration of cross-linking agent. Molecular size of the solvent is a decisive factor in the solvent uptake. The rate of sorption and maximum solvent uptake increase with increase of temperature. Irrespective of the solvents used, the maximum solvent uptake increases with increase of temperature. The observed sorptivity, diffusivity and permeability are associated with cross-link densities of different samples. The D, S and P values increase with increase of EVA content in the blend.     

The effect of process parameters on physical and mechanical properties of commercial low density polyethylene/ORG-MMT nanocomposites

Polyethylene/organo-montmorillonite clay (org-MMT) nanocomposites were prepared utilizing PP-g-MA as a compatibilizer by melt intercalation method. In order to increase the miscibility of polyethylene (PE) with nanoparticle surface at firs, a primary masterbatch consist of compatibilizer and org-MMT was prepared then, this compound was melt intercalated with PE to synthesis the PE/org-MMT nanocomposites. In this study, the presence of commercial low density polyethylene in Nanocomposites structure and also the effect of process parameters such as: amount of nanoparticles, mixing rate and mixing time on nanocomposite structure and properties have been investigated. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that the interlayer distance of nanoparticle layers increased and a partially intercalated structure was prepared by melt intercalation method. Interaction between polyethylene chains and nanoparticle layers could be improved if the control of above parameters causes to penetrate the chains into nanoclay layers; by an optimization, this effect could improve the physical and mechanical properties. The DSC data revealed that melting temperature has slowly increased and crystalinity has lightly decreased. Consequently we can claim the thermal properties of LDPE/clay nanocomposite did not considerably change with clay content. A rise in the mechanical properties such as yield stress and modulus was observed by tension test; by addition of 5% clay content the tensile strength increased about 7%, the tensile modulus enhanced about 60% and the yield stress increased about 16% in comparison with the pure LDPE.     

Preparation and properties of quercetin‐incorporated high density polyethylene/low density polyethylene antioxidant multilayer film

High density polyethylene/low density polyethylene (LDPE) antioxidant multilayer films were prepared by the co‐extrusion method, and quercetin was incorporated in the LDPE layers as an antioxidant. The release rates of quercetin and the antioxidant activities of films were adjusted by changing the amount of ethylene vinyl acetate (EVA) and diatomite added into the LDPE active layer. The morphologies of the films were observed by SEM, and the release property of quercetin was characterized by a high‐performance liquid chromatography (HPLC) method. The mechanical properties and heat sealing performance of the films were influenced to a certain extent by the amounts of EVA and diatomite in the active layers, while the barrier properties of the films were almost unchanged. The release of quercetin from the active films to a food simulant (95% alcohol) at 37°C was measured over 55 days. When the EVA amounts were 30% and 40% to 50%, the diffusion coefficients, D, were 10^?14 and 10^?13 cm²/s, respectively. In addition, the antioxidant activity values of the films were enhanced as the EVA amount increased. When adding diatomite into the active layer with 50% EVA, the diffusion coefficient, D, was 10^?11 cm²/s, and the quercetin was almost completely released with a partition coefficient, K, of less than 1. Meanwhile, the antioxidant activity values of the films exceeded 95%. The antioxidant release rate could be adjusted within a wide range; thus, these active films could be used for food antioxidant protection.     

Preparation and characterization of self-cleaning stable superhydrophobic linear low-density polyethylene

Abstract

Porous superhydrophobic linear low-density polyethylene (LLDPE) surface was prepared by a simple method. Its water contact angle and sliding angle were 153±2° and 10°, respectively. After contamination, 99% of the contaminant particles were removed from the superhydrophobic LLDPE surface using artificial rain. The superhydrophobic LLDPE surface showed high stability in the pH range from 2 to 13. When LLDPE samples were stored in ambient environment for one month, their water contact angle and sliding angle remained constant. Their superhydrophobic property was also maintained after annealing in the temperature range 10–90 °C.     

High density polyethylene (HDPE): Experiments and modeling

The uniaxial tension (loading and unloading), creep and relaxation experiments on high density polyethylene (HDPE) have been carried out at room temperature. The stress–strain behavior of HDPE under different strain rates, creep (relaxation) behavior at different stress (strain) levels have been investigated. These experimental results are used to compare the simulation results of a unified state variable theory, viscoplasticity theory based on overstress (VBO) and a macro-mechanical constitutive model for elasto-viscoplastic deformation of polymeric materials developed by Boyce et al. (Polymer 41:2183–2201, 2000). It is observed that elasto-viscoplasticity model by Boyce et al. (Polymer 41:2183–2201, 2000) is not good enough to simulate stress–strain, creep and relaxation behaviors of HDPE. However, the aforementioned behaviors can be modeled quantitatively by using VBO model.     

Lamellar orientation in the blends of linear low density polyethylene and isotactic polypropylene induced by dynamic packing injection molding

In this work, we have carried out 2 dimensional small and wide angle X-ray scattering experiments on the blends of linear low-density polyethylene (LLDPE) and isotactic polypropylene (iPP) obtained by dynamic packing injection molding in which the melt was firstly injected into the mold then forced to move repeatedly in a chamber by two pistons that moved reversibly with the same frequency as the solidification progressively occurred from the mold wall to the molding core part. iPP was found to form a shish-kebab structure with its lamellar stack oriented perpendicularly to the shear flow direction. Very interestingly, the lamellae of LLDPE were found tilted away from shear flow direction with molecular chain still along flow direction, and the tilted angle increases from the skin to the core part. This can be only understood if the intra-lamellar block slip in the chain direction is generally activated during shearing process achieved by dynamic packing injection molding. Our finding is important and seems to provide further support for the idea that the structure of the crystalline lamellae is not continuous but constructed of small building units with thin boundary in between.     

Polycarbonate-linear low density polyethylene blends: Thermal and dynamic-mechanical properties

Blends of polycarbonate (PC) and linear low density polyethylene (LLDPE) of different compositions, in the form of slabs obtained by melt extrusion, have been examined by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA).DSC measurements show that the melting, crystallization and glass transition temperatures of the two polymeric components in the blends are slightly affected by the composition. On the contrary, large differences are observed in the melting behaviour of layers cut at various depths, parallel to the slab surfaces of samples. This supports the occurrence of different crystal morphologies and distribution of the two components within the samples. The study of the crystallization kinetics from the melt blends shows that the crystallization processes of LLDPE are affected by the presence of PC.The dynamic mechanical analysis indicates that modulus, transitions and relaxational behaviour of the polymer components are scarcely affected by the composition. Some variations of the damping factor have been interpreted as due to the phase heterogeneity of the system, arising from the processing conditions and rheological behaviour of the blends.     

Morphology and mechanical property relationship in linear low-density polyethylene blown films

Linear low-density polyethylene (LLDPE) blown films fabricated under two different processing conditions, namely a non-stalk bubble configuration and a stalk bubble configuration, were investigated. Morphological characterization was performed using small-angle X-ray scattering, transmission electron microscopy, infrared dichroism, and differential scanning calorimetry. The findings on crystal orientation characteristics of the films suggest that modification on the widely accepted row orientation model of Keller and Machin may be needed. In comparison to the conventional non-stalk bubble geometry for LLDPE film blowing, the stalk bubble configuration can produce a more randomly orientated lamellar texture, resulting in less anisotropy in mechanical properties and a higher dart impact resistance. A good correlation between mechanical properties and morphological features was found.