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.     

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.     

Space charge relaxation in high density polyethylene (HD-PE)

A general order kinetics approach has been used to study the space-charge relaxation in highdensity polyethylene (HD-PE). The analysis of the activation energy,E, and the kinetics order,q, allows the determination of two relaxation regions above the glass transition temperature; one between −24 and 16° C, and a second above 16° C. Both relaxations are discussed on the basis of the structural characteristics of polyethylene.     

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%.     

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.     

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℃。      

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.     

Tensile force at break of gel-spun/hot-drawn ultrahigh molecular weight polyethylene fibres

Fibres obtained by gel spinning of ultrahigh molecular weight polyethylene (UHMWPE) were drawn to various ratios, and the improvement of the tensile strength of the hot-drawn filaments with increasing draw ratio has been studied. The tensile force at break of gel-spun/hot-drawn UHMWPE fibres appeared to be constant for draw ratios exceeding λ=30. From scaling arguments, full chain extension is expected at this draw ratio. On the basis of development of the physical properties during drawing, it is concluded that little disentangling occurs up to λ=30. Beyond this point, slippage of chains through entanglement hooks becomes predominant. The observed constant tensile force at break can be explained by this drawing mechanism.     

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.     

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.     

纳米ZnO/低密度聚乙烯复合材料的介电特性

为探讨纳米ZnO/低密度聚乙烯（LDPE）复合材料的介电特性,首先,采用硅烷偶联剂和钛酸酯偶联剂对纳米ZnO进行改性,并利用两步法制备了不同纳米ZnO质量分数、不同纳米ZnO粒径、不同纳米ZnO表面修饰方式和不同冷却方式的纳米ZnO/LDPE复合材料;然后,通过FTIR、SEM、DSC和热激电流（TSC）测试了纳米ZnO在基体中的分散情况、复合材料的等温结晶过程参数变化及陷阱密度;最后,在不同实验温度下分别进行了交流击穿、绝缘电导率、介电常数和空间电荷实验。结果表明:纳米ZnO的加入使纳米ZnO/LDPE复合材料内部陷阱深度和密度均有所增加;当纳米ZnO的粒径为40 nm且质量分数为3%时,复合材料的结晶速度最快,纳米ZnO在基体中的分散性较好,击穿场强达到最高值133.3 kV/mm,电导率及介电常数也相对较低,加压时复合材料内部空间电荷少,短路时释放电荷速度快,介电性能较好;由于纳米粒子增加了材料内部的热传导速率,降低了复合材料随着温度升高而降解的速度,因而相对于纯LDPE,随着实验温度的提高,纳米ZnO/LDPE复合材料的击穿场强下降幅度及电导率上升幅度均较小。      

Slurry erosion behaviors of basalt filled low density polyethylene composites

In this study, slurry erosion behaviors of basalt filled low density polyethylene composites were investigated. Pure low density polyethylene and four different compositions of the composites 10 wt.%, 30 wt.%, 50 wt.% and 70 wt.% basalt were used in the study. Slurry wear, tensile strain, hardness and fracture toughness tests were performed on the samples. Samples turns in the abraded slurry media including 50 wt.% Al₂O₃ with nominal particle size of 500 μm and the erosion tests of pure low density polyethylene and basalt filled composites were performed at the contact angles of 15°, 30°, 45°, 60°, 75° and 90° for 30 min. in 3 periods at 500 rpm turning speed (1 m/s speed). It was observed that erosion rate have no effect up to 30 wt.% basalt content. Wear resistance of the composites including over 30 wt.% basalt were micro structural examination of the worn samples showed that the basalt particles on the worn surface can be sustained by matrix. Basalt particles were worn more slowly than that of the matrix. The more the basalt content in the basalt filled low density polyethylene resulted to the lower the tensile strength, tensile strain and fracture toughness, and the higher the hardness. The slurry erosion rate of the basalt filled low density polyethylene composites was getting sharply increase above 30 wt.% basalt content above 60° contact angle.     

Comparative sorption of citrus flavor compounds by low density polyethylene

Mixtures of seven characteristic flavor solutes commonly found in orange juice were studied for their interaction with low-density polyethylene (LDPE) from aqueous solutions at 20°C. Precautions were taken to avoid thermal and chemical degradation of the flavor solutes and degradation components were not found by HPLC analysis. Hydrocarbon monoterpenes showed 30–40% sorption by the LDPE over a 25-day period. Oxygenated monoterpenes showed ca. 10% sorption in the same time period. Further study of one of the hydrocarbon terpenes (d-limonene) showed both adsorption (surface attraction) and absorption (matrix dissolution), while its analogous oxygenated terpene (I-carvone) displayed predominantly adsorption. These findings are useful for deciding proper compensations for changes in flavor profiles in packaged orange juices in contact with LDPE. They also illustrate the importance of learning the nature of polymer-flavour interactions between foods and packaging materials.     

Stress relaxation behaviour of some aromatic compounds and their alloys with linear polyethylene

The paper reports on stress relaxation measurements on piperonal, camphor and dimethyl terephthalate (DMTP), and on alloys of high density polyethylene (HDPE) with camphor, DMTP and thymol. The pure compounds were measured in compression, the HDPE-alloys in tension. The course of the relaxation curves is in certain cases complicated by recrystallization of the low molecular weight substances and also by sublimation stresses. When these effects are accounted for, the previously found general relationship between the slopeF of the curves, (dσ/d Int)_max, and the initial effective stress, σ ₀ ^* , i.e. $$F = (0.1 \pm 0.01)\sigma _0^* $$ is confirmed. The results thus extend the validity of this structure-independent relation to low molecular weight aromatic substances and their alloys with a crystalline polymer.     

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...