Surface modification of low density polyethylene (LDPE) film by low pressure O2 plasma treatment

In this work, low pressure glow discharge O₂ plasma has been used to increase wettability in a LDPE film in order to improve adhesion properties and make it useful for technical applications. Surface energy values have been estimated using contact angle measurements for different exposure times and different test liquids. In addition, plasma-treated samples have been subjected to an aging process to determine the durability of the plasma treatment. Characterization of the surface changes due to the plasma treatment has been carried out by means of Fourier transformed infrared spectroscopy (FTIR) to determine the presence of polar species such as carbonyl, carboxyl and hydroxyl groups. In addition to this, atomic force microscopy (AFM) analysis has been used to evaluate changes in surface morphology and roughness. Furthermore, and considering the semicrystalline nature of the LDPE film, a calorimetric study using differential scanning calorimetry (DSC) has been carried out to determine changes in crystallinity and degradation temperatures induced by the plasma treatment. The results show that low pressure O₂ plasma improves wettability in LDPE films and no significant changes can be observed at longer exposure times. Nevertheless, we can observe that short exposure times to low pressure O₂ plasma promote the formation of some polar species on the exposed surface and longer exposure times cause slight abrasion on LDPE films as observed by the little increase in surface roughness.     

Modification of surface properties of high and low density polyethylene by Ar plasma discharge

Structural changes induced by Ar plasma discharge in low and high density polyethylene (LDPE and HDPE) were studied by different techniques. AFM and SEM methods were used to determine surface morphology, the changes in chemical structure were followed using FTIR and UV-vis spectroscopy. The content and the depth profile of incorporated oxygen was determined by RBS method. The degree of polymer ablation was determined gravimetrically. Standard goniometry was used to determine contact angle and to follow aging of plasma modified polymer. As a result of plasma treatment a lamellar structure or spherulites appear on the surface of HDPE and LDPE, respectively. Pronounced increase of the surface roughness is observed on HDPE contrary to LDPE. Plasma treatment for 400 s leads to the ablation of the surface layer of about 0.6 and 1 μm thick for LDPE and HDPE, respectively. Plasma treatment results in oxidation of the polymer surface layer which is more pronounced in HDPE. Concentration maximum of incorporated oxygen lies 25 nm beneath the sample surface in both polymer types. After exposure to plasma discharge carbonyl, carboxyl and amide groups were detected in the polymer surface layer together with CC bonds either in aromatic or in aliphatic structures. Immediately after the plasma treatment strong decline of the contact angle is observed, the decline being larger in HDPE. Later, in aged specimens the contact angle increases rapidly. The increase, which may be due to rearrangement of degraded structures, is stronger in the specimens exposed to plasma for longer times.     

电火花引发HEMA 接枝LDPE 薄膜及其血液相容性

采用接枝量、ATR－IR、SEM、与水接触角、溶血试验和再钙化时间等测试手段研究了电火花引发甲基丙烯酸β－羟乙酯(HEMA)表面接枝低密度聚乙烯(LAPE)薄膜的接枝聚合反应影响因素、表面结构和血液相容性。结果表明,电火花能有效引发HEMA在LDMA薄膜表面接枝聚合反应,随接枝聚合反应时间延长、单体浓度的增大。接枝量增大。随反应温度升高,接枝量增大到一最大值后,进一步升高反应温度,接枝量下降,最佳接枝聚合温度为60℃当在60℃单体φ=5％水溶液是反应2h时,经空气气氛和1.5kV电火花预处理72s和LDPE薄膜表面接枝量可达169ug/cm^2。接枝改性后LDPE薄膜与水的接触下降,亲水性增加,溶血程度减小,再钙化时间延长,血液相容性得到改善。     

Surface changes brought about by corona discharge treatment of polyethylene film and the effect on subsequent microbial colonisation

Microbial colonisation of synthetic plastic films is normally slow, which affects the total period of biodegradation. Correlation between the modified surface condition and the ability for microorganisms to colonise low-density polyethylene (LDPE) film was studied. Corona discharge treatment was applied to obtain enriched and activated surface condition of LDPE film. It was found from water contact angle and FTIR spectrum evaluations that surface energy was significantly increased due to production of free radicals. Stabilised oxidised LDPE surface was also obtained by further exposure to the corona which gave more suitable condition for subsequent colonisation. Results were compared with UV irradiated (photo-oxidised) LDPE films. Colonisation of corona discharged and UV treated LDPE films were tested in the laboratory environment using known fungal isolates and in a natural compost environment. More active microbial colonisation was observed in all cases for corona discharged and UV treated LDPE films. Far longer UV exposure was required to have the same physicochemical and biological effect as the corona discharge treatment.     

Macromolecular scission and crosslinking rate changes during polyolefin photo-oxidation

Chain scission and crosslinking rates have been derived from molecular mass distributions obtained by gel permeation chromatography at different stages during photodegradation of various thermoplastics exposed to ultraviolet irradiation (UV). Results are given for a high density polyethylene (HDPE); a low density polyethylene (LDPE); a linear low density polyethylene (LLDPE); a polypropylene homopolymer (PPHO); and a polypropylene copolymer (PPCO). As the oxidation progressed, it was observed that the scission rate for HDPE, LLDPE, PPHO and PPCO increased near to the exposed surface whereas for LDPE the rate remained almost unchanged. The crosslink rate fell near to the surface with HDPE and LDPE but increased with PPHO and PPCO. The reaction rates near to the bar centre (∼1.5 mm from the exposed surface) were low for HDPE, PPHO and PPCO; this is attributed to oxygen starvation, caused by consumption of oxygen by rapid reaction near the surface. Reaction was observed in the interior with LDPE and LLDPE, presumably because of a combination of a higher oxygen diffusion rate than for HDPE and a lower rate of consumption of oxygen near the surface than with the polypropylenes.     

氧等离子体改性聚乙烯表面的疏水性过回复机制

用200 W射频容性耦合氧等离子体处理低密度聚乙烯(LDPE)表面1 min, 研究了老化温度及时间对LDPE表面成分、 形貌和润湿性的影响. 扫描电子显微镜结果表明, 等离子体改性LDPE表面出现纳米凸点织构, 在60和90 ℃老化24 h后纳米凸点织构特征基本保持稳定. X射线光电子能谱分析表明, 等离子体改性LDPE表面经60 ℃老化24 h后, C—C含量由76.9%增至83.0%, C—O, CO和O—CO含量分别由16.4%, 2.2%和4.5%降至13.1%, 1.9%和2.0%. 经90 ℃老化24 h后, C—C含量较60 ℃老化表面增至84.1%, C—O含量分别降至10.1%, CO和O—CO含量分别增至3.1%和2.7%. 等离子体改性LDPE表面接触角由97.2°降至42.3°, 经60 ℃老化24 h后接触角增至95.9°, 经90 ℃老化24 h后接触角增至104.2°, 等离子体改性LDPE表面发生“疏水性过回复”. 根据含有粗糙因子的接触角随时间演变模型, 得到了具有纳米凸点织构LDPE表面在不同老化温度下的可移动极性基团所占面积分数(\begin{array}{c}{f}_m^p\end{array})、 固定极性基团所占面积分数(\begin{array}{c}{f}_{\mathit{im}}^p\end{array})和特征时间常数(τ)3个成分重构参数, 解释了“疏水性过回复”现象.     

紫外光引发LDPE膜接枝含氟丙烯酸酯的研究

通过紫外光引发表面接枝聚合反应的方法 ,把含氟丙烯酸酯单体R 5 6 1 0引到LDPE薄膜上 .对经丁酮抽提后的接枝膜进行FTIR、ESCA、SEM和DSC等表征 ,证实含氟聚合物以化学键的方式接枝在LDPE基体膜上 .在一定范围内 ,增加紫外光强、引发剂和单体浓度以及反应温度等均有利于提高接枝率 .经计算R 5 6 1 0的紫外光引发接枝聚合反应总活化能为 5 4 2kJ mol.接枝膜的接触角随着接枝率的提高逐步增大 ,直至趋于恒定 .作者提出接枝膜存在一个在接触角测定时影响基体膜与探测水滴相互作用过程的边界层 .当接枝率较低、接枝层厚度小于边界层临界厚度时 ,基体LDPE影响接触角的大小 ,但随着接枝率提高 ,接枝层逐渐变厚 ,氟聚合物层对接触角的贡献逐渐占优势 ,导致接触角随之增大 .当接枝率超过一定值以后 ,接枝层厚度超过边界层临界厚度 ,接枝层对接枝膜的接触角起全部贡献 ,接触角测定值随之稳定     

Surface Properties of Low Density Polyethylene upon Low-Temperature Plasma Treatment with Various Gases

The surface of a LDPE was modified by Ar, O₂, N₂, CO₂ gaseous plasma. The changes in surface morphology and surface wettability were investigated using AFM and SEM. The surface chemical changes of LDPE were also characterized by FTIR-ATR. The SEM and AFM results demonstrated variable changes in surface roughness for different types of plasma gas used, the changes being more for the Ar and N₂ plasma treatments. Considering the nature of the LDPE film, XRD studies were carried out to determine changes in the percentage crystalinity. The results showed that all low pressure O₂, Ar, N₂, CO₂ gas plasmas improved the wettability of LDPE films. Contact angles decreased significantly depending on the discharge powers and exposure times. Surface morphology was also found to vary with plasma discharge powers, exposure times, and the type of gas being used. Ar and N₂ gas plasmas in general produced more superior results.     

Studies on reactive blending of LDPE and cenosphere

The present work aims to modify conventional low density polyethylene (LDPE) by preparing its particulate composite with cenosphere. Cenosphere is a potential waste produced in bulk from the coal fired thermal power plant. In this context, surface modification of cenosphere was done by γ- aminopropyl triethoxy silane (ATS) coupling agent. Furthermore, LDPE was grafted by glycidyl methacrylate (GMA) to be used as compatibilizer. The resulting surface modified and unmodified cenosphere as well as glycidyl methacrylate grafted LDPE (LDPE-g-GMA) were functionally characterized by Fourier Transform Infrared (FT-IR) spectroscopy. LDPE-cenosphere particulate composites were processed in their different formulations and evaluated with various properties such as thermal stability, mechanical properties, chemical resistance and flow behaviour. Dispersibility of cenosphere in LDPE matrix was studied by Scanning Electron Microscopy (SEM). Series of analysis was performed in order to understand the effect of cenosphere content and its modification on the final properties of particulate composites. Mechanical properties were found to be statistically significant as per ANOVA and Post hoc Tukey HSD test. Particulate composites prepared with modified interphase were observed to possess good combination of properties.     

Surface ozonation and photooxidation of polyethylene film

High-density polyethylene (HDPE) and low-density polyethylene (LDPE) films were oxidized by treatment with ozone and by photooxidation with a low-pressure mercury lamp. The changes that resulted in the surfaces of the films were followed by ESCA. On ozonation, the surface of LDPE initially is oxidized more rapidly than that of HDPE; however, extended ozonation produces a surface composition that corresponds to C₈O for HDPE and to C₁₈O for LDPE. The surface oxidation products are mainly carboxyl groups, with lower levels of carbonyl and C? O groups. For both polymers photooxidation provides more extensively oxidized surfaces than ozonation, although the surface of HDPE oxidizes slightly faster than that of LDPE treated under identical conditions. In both cases the surface stoichiometry after extensive photoxidation is C₆O. The functional groups formed are mainly carboxyl and C? O. The effects of ozonation and photooxidation on the polyethylene surfaces are compared with those produced by several other means of surface oxidation.     

Effect of surface oxyfluorination on the dyeability of polyethylene film

The effect of surface oxyfluorination on low-density polyethylene (LDPE) film was studied in terms of surface functionality and surface energetics of the film surfaces, which can be attributed to improvement of the dyeability. The growth of functional groups and surface free energy was confirmed by FTIR-ATR, XPS, and contact angle methods. As a result, the total surface free energy was increased with oxyfluorination time, as a progressive increase of the polar component together with a small decrease of the dispersive component of surface free energy. From the dyeability test using the Kubelka-Munk equation, it was found that the oxyfluorination treatment plays an important role in the growth of oxygen-containing functional groups of LDPE film, resulting in improving the dyeability with a basic dyeing agent. A direct linear relationship is shown between the specific component of surface free energy and the K/S value for this work.     

Effect of carbon-black treatment by radiation emulsion polymerization on temperature dependence of resistivity of carbon-black-filled polymer blends

High dispersibility and stability of carbon black particles in low-density-polyethylene (LDPE) matrix were obtained by radiation emulsion polymerization on carbon particles surface, and electrical resistivities of its simple were examined. First carbon particles treatment on radiation emulsion polymerization on surface were synthesized by the reaction with a polymer-emulsion systems containing reactive group in the molecular unit, carbon particles and emulsifier. Then, the carbon particles treatment on radiation emulsion polymerization on surface was dispersed into LDPE, and its composites were prepared for electrical measurements. The effect of radiation crosslinking of the composite on the Positive temperature coefficient (PTC) and negative temperature coefficient (NTC) phenomenon was investigated. The experimental results showed that PTC and NTC effects of the composites were obviously influenced by the irradiation dose. Various microstructure-exploring means were used to study the conductive composite, such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM).     

A novel superhydrophobic surface based on low‐density polyethylene/ethylene‐propylene‐diene terpolymer thermoplastic vulcanizate

A novel superhydrophobic surface based on low‐density polyethylene (LDPE)/ethylene‐propylene‐diene terpolymer (EPDM) thermoplastic vulcanizate (TPV) was successfully fabricated where the etched aluminum foil was used as template. The etched aluminum template, consisted of countless micropores and step‐like textures, was obtained by metallographic sandpaper sanding and the subsequent acid etching. The surface morphology and the hydrophobic properties of the molded TPV surface were researched by using field emission scanning electron microscope and contact angle meter, respectively. From the microstructure observation of the superhydrophobic LDPE/EPDM TPV surface, the step‐like textures obtained via molding with etched aluminum foil template and a large number of fiber‐like structures resulted from the plastic deformation of LDPE matrix could be found obviously. The obtained TPV surface exhibited remarkable superhydrophobicity, with a contact angle of 152.0° ± 0.7° and a sliding angle of 3.1° ± 0.8°.     

Effects of flame treatment on the interfacial energy of polyethylene assessed by contact mechanics

The effects of flame treatment of low-density polyethylene (LDPE) on the work of adhesion (W) and energy release rate (G) were assessed by a custom-built adhesion testing device (ATD). The contact area and the vertical displacement between planar LDPE films and PDMS lenses (untreated and UV/ozone treated) were varied as a function of the applied load, P. The adhesion and pull-off forces between the extracted PDMS lenses and the LDPE films were studied as a function of the duration of the flame treatment expressed in treatment numbers. A fracture mechanics approach was used to relate the applied load and the radius of the contact area to the energy release rate (G). The difference between the energy release rate and the thermodynamic work of adhesion, defined as the adhesion hysteresis (G - W), increased systematically with increasing treatment numbers for both lens types. In addition, the adhesion hysteresis appeared to be dependent on the contact time. Finally, the origin of the adhesion hysteresis was discussed. It was concluded that bonding by surface functional groups may be the dominating mechanisms for the changes in the observed hysteresis.     

以多孔CaCO3微球为模板制备聚乙烯超疏水表面

以聚苯乙烯磺酸钠（PSS）掺杂的多孔碳酸钙（CaCO3）微球层为模板,通过热压低密度聚乙烯（LDPE）并结合酸蚀刻的方法制得了具有多层粘联微球结构、而非常见蜂窝状多孔结构的LDPE稳定超疏水表面（接触角152.8±2.5°,滚动角约6°）。元素分析表明,表面粘联微球为纯LDPE而非LDPE包覆的CaCO3。将多孔CaCO3微球稀疏地撒在LDPE表面并加热熔融,发现微球会自发沉降到熔体内部,酸蚀刻后形成了类似莲蓬的表面微结构,即坑内包含小球。结合CaCO3微球生成原理和多孔结构,认为粘联微球结构和莲蓬结构均是由于LDPE熔融大分子自发沉积到多孔CaCO3微球内部,“反模”形成了LDPE微球所致。本发现为多孔CaCO3微球的应用开辟了新方向。     

The mechanical properties of LDPE composite filled with CF coated by dimethylamine treated TiO2

In order to improve the surface wettability of carbon fiber and enhance its composite interface performance, dimethylamine treated TiO2 was coated on carbon fiber (CF). The surface morphology, surface chemical state, and surface wettability of CF were characterized by SEM, XPS, and TEM tests, and the interlaminar shear strength (ILSS) and cross-sectional morphology tests were used to test the performance of CF/Low density polyethylene (LDPE) composites. The interface bonding status was analyzed and characterized. The results show that after the surface treatment of CF by dimethylamine treated TiO2, the O/C (atomic ratio) of the surface of CF is increased, and a certain amount of nano-scale small convex micro-mechanical structure is given, which improves the surface wetting of CF. The surface of the CF modified by the TiO2 is rough; the contact area between modified CF and LDPE increases.     

Characterization of carboxylate sites in surface oxidized polyethylene films by fluorescence techniques

Oxidized reactive sites introduced by controlled chemical reactions in non-crystalline regions of semi-crystalline polyolefin films are located mainly on the film surface or in adjacent subsurface regions. The so-formed reactive sites in low density polyethylene (LDPE) blown films were labelled by fluorescent groups and investigated by various fluorescence techniques. The surface or subsurface location of the labelled site is indicated by a solvatochromic spectral shift and confirmed by the polarity dependent fluorescence lifetime of the labelled LDPE film immersed in a polar liquid. Fluorescence concentration quenching and concentration depolarization demonstrate the high density of oxidized sites near the film surface. The measurement of rotational mobility and orientation during film stretching adds further experimental tools to distinguish reactive oxidized sites in the surface or in the bulk.     

Effect of the presence of silica nanoparticles in the coefficient of thermal expansion of LDPE

The effect of the presence of alumina microparticles and silica nanoparticles on the coefficient of thermal expansion (CTE) of films of low density polyethylene (LDPE) based composites was investigated. A new method based on the use of an atomic force microscope (AFM) is proposed for measuring nano-thermal expansion of films to finally obtain the CTE in polymer based materials. Nanocomposites based on silica nanoparticles and LDPE were prepared by mixing those constituents by high energy ball milling (HEBM). Pure alumina microparticles come from the milling tools used to mix the components of the composites. When silica nanoparticles are used as nanofiller of LDPE the effectiveness on reducing the CTE (about a 40% of CTE reduction) is higher than that obtained when high amount of alumina microparticles are present in the LDPE. Only when high amount of silica nanoparticles and low amount of alumina microparticles are present, the reduction of CTE expected from the Levin model is in accordance with the experimental results. This effect was associated to the high surface to volume ratio of nanoparticles considering uniform dispersions of them within the polymer. The region of polymer between particles must be so thin (few nanometers) that constraint effects must play an important role on reducing the chain mobility and therefore the thermal expansion.     

Morphology studies and ac electrical property of low density polyethylene/octavinyl polyhedral oligomeric silsesquioxane composite dielectrics

This paper presents the results of morphological and ac electrical investigations on low density polyethylene (LDPE) composites with octavinyl polyhedral oligomeric silsesquioxane (POSS). It has been shown that at low loadings, the frequency dependence of dielectric constant and dielectric loss for the LDPE/POSS composites showed unusual behaviors when compared with conventional (micro-sized particulates) composites. The ac breakdown strength was measured and statistical analysis was applied to the results to determine the effects of POSS loadings on the dielectric strength of LDPE. The morphological characterization showed that the presence of POSS additives apparently altered the supermolecular structure of LDPE and resulted in more homogeneous morphology when compared with the neat LDPE. The structure-property relationship was discussed and it was concluded that the final dielectric properties of the composites were determined not only by the incorporation of POSS additives but also by the supermolecular structure of LDPE. Rheological analyses of LDPE/POSS composite were also performed and the results showed that the octavinyl-POSS had good compatibility with LDPE.