Modification of Low Density Polyethylene with 2-Hydroxyethyl Acrylate by a Swollen-Phase Grafting Method

Low-density polyethylene (LDPE) was modified with 2-hydroxyethyl acrylate (HEA) by a swollen phase grafting method with azobisiso-butyronitrile (AIBN) as initiator and xylene as a swelling agent. Fourier transform infrared spectroscopy (FTIR) and ¹H-nuclear magnetic resonance (¹H-NMR) showed that the HEA was grafted onto the PE molecular chains and the copolymer (LDPE-g-PHEA) was formed. The rheological data illustrated that the content of long chain branches (LCB) in LDPE-g-PHEA was higher than in LDPE. Melt flow index (MFI) measurements indicated that the LDPE backbone was degraded slightly when the HEA content was small in the process of grafting. X-ray diffraction (XRD) and water contact angle measurements demo-nstrated that the grafting degree had an influence on the crystallinity and polarity of the graft polymer. A staining analysis indicated that the dyeing of the product was improved continuously with increasing of the grafting degree. Polyvinylpyrrolidone (PVP), NaCl, and ultrasound were shown to contribute to the staining, with ultrasound being the most productive. The probable grafting reaction mechanism is pro-posed. The results of the influence of monomer concentration on the grafting reaction revealed that the grafting ratio and gel content of the product increased with increasing of HEA amount.     

Comparison of optical properties and mechanical/electrical degradation of some low density polyethylene-and polypropylene-based polymer blends

In this study, the optical properties as well as mechanical and electrical degradation of low-density polyethylene (LDPE)/polypropylene fiber (PP fiber) (10–50% PP fiber), polypropylene (PP)/PP fiber (10–50% PP fiber), and LDPE/diamond (0.1–3% diamond) blends, which are prepared by hot pressing method, with changing thicknesses ranging from 30 to 225 μm, are compared. The spectra, in the wavelength range 200–2500 nm, are examined. Based on optical absorption spectra obtained, Tauc graphs are plotted. Determined values of the direct optical energy gap (E _d ^opt ), the indirect optical energy gap (E _i ^opt ), the width of the band (ΔE), and ultraviolet transmittance (T_UV) are listed. The direct E _d ^opt and indirect E _i ^opt values for organic blends are in the range of 3.10–3.17 eV and 1.52–2.99 eV; for inorganic blends they are 1.80–4.13 eV and 1.55–4.7 eV respectively. The electrical strength (ε) and the mechanical tension (σ) have been investigated, and graphs (the dependence of the electrical life time log τ_ε on ε) are given. The experimental results are analyzed from the viewpoint of the validity of the thermofluctuation theory. LDPE and LDPE/0.5% diamond composite parameters consecutively changed: σ from 68 to 82 MPa, ε from 60·10⁶ to 85·10⁶ V/m, mechanical lifetime τ_σ from 10 to 1.5·10⁵ sec, electrical lifetime τ_ε from 2· 10³ to 2·10⁵ sec, and structure-sensitive parameters γ and χ — from 1.48 to 1.18 (J)MPa/mole and from 0.97 to 0.70 (J)Vm⁻¹/mole respectively. The values of mechanical and electrical durability were observed to increase by 20 and 41%, respectively, for LDPE/0.5% diamond composite. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 677–683, September–October, 2007.     

LDPE phase composition in LDPE/Cu composites using thermal analysis and FTIR spectroscopy

Low-density polyethylene (LDPE) films with different copper contents were prepared from solu-tion. The TGA (thermogravimetric analysis) results show that the presence of copper particles can im-prove the thermal stability of the composite since a maximum increment of 14°C is obtained compared with the pure LDPE in this experiment. The results of DSC (differential scanning calorimetry) in stan-dard conditions show that the Cu content has little influence on the crystallinity, X _c , of LDPE. But a trace of DSC under non-standard conditions suggests that the presence of the copper microparticles has a greater effect on the network phase than on the crystalline long-range-order phase. FTIR spectroscopy was used to study the phase content of LDPE in LDPE/Cu non-oriented composite films prepared from solution with different copper contents by analysis of CH₂ rocking vibrations. A spectral simulation of transmission spectra performed using a two-phase model does not show any variation into the phase composition of the LDPE matrix for all copper contents. When a three-phase model was taken into account, the amount of the orthorhombic phase was found to be constant. However, the fraction of the amorphous and that of the network phase were found to increase and decrease respectively with increase in the copper particle load in the film.     

Interfacial structure analysis of polymer laminate using SPring-8 X-ray microbeam

Interfacial structure of laminated polyethylene (PE)/polypropylene (PP) films was investigated by synchrotron X-ray microbeam. The X-ray microbeam (0.9 μm (vertical) × 1.7 μm (horizontal)) formed using a phase zone plate was irradiated on the cross-section of the laminated films. In order to irradiate X-ray microbeam in the direction perpendicular to the cross-section of the film sample, adjustment of the sample setting was performed by Thomson scattering method. The Thomson scattering intensity is proportional to the number of the irradiated electrons, so the irradiated position of the X-ray microbeam could be determined from the intensity profile with high spatial resolution. By changing the sample position, diffraction patterns could be obtained from the laminated films across the PE/PP interfacial region. The thickness of the interfacial region of the annealed laminate was estimated as 5 μm judging from the changes of the diffraction intensities from the PE crystallites to the PP ones. The interfacial thickness depended on the thermal treatment of the film. It was found that the adhesion strength of the PE/PP laminate increased with increasing the interfacial thickness. Both of PE and PP chains entangled each other during laminate processing. The entangled molecular chains play important role as anchoring effect at the PE/PP interdiffusion region. However, the phase separation progressed with further crystallization by annealing. Thus, the adhesion strength of the PE/PP laminate was considered to be influenced by the interfacial thickness.     

Highly adhesive metal plating on Zylon fiber via iodine pretreatment

Highly adhesive metal plating was performed on poly(p-phenylene-2,6-benzobisoxazole) fiber named Zylon^® via iodine pretreatment followed by electroless plating. First, iodine components were selectively doped into the inner part of the fiber near the surface through iodine vapor exposure. The doped iodine was converted to palladium iodide particles by treating with palladium chloride solution. After the reduction of the iodide to metal palladium particles, electroless copper plating was conducted on the fiber. A uniform copper layer was deposited on the fiber surface and exhibited high durability in durability tests such as ultrasonic exposure, tape peeling-off, and corrosion in NaCl solution. This durability was attributed to the palladium particles formed at the fiber surface that served as an anchor for the plated layer as well as an electroless plating catalyst. The plated fibers also possessed electrical conductivity. Although the tensile strength of the Zylon^® fiber decreased from 5.8 to 4.9 GPa after undergoing the pretreatment and plating processes, the light shielding effect improved the light resistance of the plated fibers in terms of tensile properties. After 18 days of xenon lamp exposure, the plated fibers retained 74% of its initial strength, whereas that of untreated fibers decreased to 43%.     

Effect of Polyethylene Functionalization on Mechanical Properties and Morphology of PE/SiO2 Composites

In this study composites of high density polyethylene (HDPE) with various SiO₂ content were prepared by melt compounding using maleic anhydride grafted polyethylene (PE-g-MAH) as a compatibilizer. The composites containing 2, 4 and 6% by weight of SiO₂ particles were melt-blended in a co-rotating twin screw extruder. In all composites, polyethylene-graft-maleic anhydride copolymer (PE-g-MAH, with 0.85% maleic anhydride content) was added as a compatibilizer in the amount of 2% by weight. Morphology of inorganic silica filler precipitated from emulsion media was investigated. Mechanical properties and composite microstructure were determined by tensile tests and scanning electron microscopy technique (SEM). Tensile strength, yield stress, Young's modulus and elongation at break of PE/SiO₂ composites were mainly discussed against the properties of PE/PE-g-MAH/SiO₂ composites. The most pronounced increase in mechanical parameters was observed in Young's modulus for composites with polyethylene grafted with maleic anhydride. The increase in the E-modulus of PE/PE-g-MAH/SiO₂composites was associated with the compatibility and improvement of interfacial adhesion between the polyethylene matrix and the nanoparticles, leading to an increased degree of particle dispersion. This finding was verified on the basis of SEM micrographs for composites of PE/PE-g-MAH/4% by weight of SiO₂. The micrographs clearly documented that addition of only 2 wt% of the compatibilizer changed the composite morphology by reducing filler aggregates size as well as their number. Increased adhesion between the PE matrix and SiO₂ particles was interpreted to be a result of interactions taking place between the polar groups of maleic anhydride and silanol groups on the silica surface. These interactions are responsible for reduction of the size of silica aggregates, leading to improved mechanical properties.     

Effect of Processing Conditions on Heat Seal Strength for Peelable Heat Sealing of Multilayered Polyethylene Films with Different Sealant Layers

The effect of heat sealing temperature on peelable heat seal strength (HSS) before and after the sterilization, often used industrially, was investigated for one of either polyethylene (PE) multilayered films with various inner sealant layers consisting of two high density PEs (HDPEs), a linear low density PE (LLDPE) or low density PE (LDPE). To attain similar HSS, heat sealing at a temperature close to the melting peak temperature (Tm-p) was needed only in the case of LDPE. Heat sealing behavior at higher temperatures, to attain higher HSS, was also investigated for HDPE and LDPE. High HSS, as well as suppressed reduction of HSS after the sterilization, was achieved for HDPE at a heat sealing temperature well below its Tm-p. An Increase of HSS with the increase of dwell time was also observed. On the other hand, for LDPE, high HSS and its stability after the sterilization were achieved only when the heat sealing temperature was increased to the value equivalent to its Tm-p. Improvement of the processing conditions for the shortening of the processing period was also investigated. For HDPE, higher sealing bar temperature was needed to gain similar HSS when the dwell time of the heat sealing was shortened from 4 to 2 s, whereas the attained maximum temperature at the interface was found to be similar. The characteristics of the heat sealed portion, judged from the relation between HSSs before and after the sterilization, were not affected by the dwell time of heat sealing, indicating that the shortening of the processing time by appropriate raising of the sealing bar temperature is possible.     

Flame treatment of low-density polyethylene: Surface chemistry across the length scales

The relationship between surface chemistry and morphology of flame treated low-density polyethylene (LDPE) was studied by various characterization techniques across different length scales. The chemical composition of the surface was determined on the micrometer scale by X-ray photoelectron spectroscopy (XPS) as well as with time of flight secondary ion mass spectrometry (ToF-SIMS), while surface wettability was obtained through contact angle (CA) measurements on the millimeter scale. The surface concentration of hydroxyl, carbonyl and carboxyl groups, as a function of the “number” of the flame treatment passes (which is proportional to the treatment time) was obtained. Moreover, a correlation was found with chemical composition and polarity, emphasizing the role of oxygen-containing functional groups introduced during the treatment. Carboxyl functional groups were specifically identified by fluorescent labeling and the results were compared with the ToF-SIMS data. In addition, atomic force microscopy (AFM) was used to evaluate changes in surface topography and roughness on the nanometer to micrometer length scales. After flame treatment, water-soluble low molecular weight oxidized materials (LMWOM), which were generated as products of oxidation and chain scission of the LDPE surface, agglomerated into small topographical mounds that were visible in the AFM micrographs. After rinsing the flame treated samples with water and ethanol, bead-like nodular surface structures were observed. The ionization state of flame treated LDPE surfaces was monitored by chemical force microscopy (CFM). The effective surface pK_a values of carboxylic acid (-COOH) obtained by AFM were revealed by chemical force titration curves and the effective surface pK_a values were found to be around 6.     

外力诱导吸附高分子单链的拉伸分子动力学研究

采用拉伸分子动力学方法研究聚乙烯单链在真空中从一个强吸附表面被拉伸的动力学过程. 当聚乙烯单链从中间1/3处被拉伸时,通过理想弹簧可测量其平均力〈f〉,发现在拉力与拉伸距离的曲线上出现了两个平台,这与实验结果非常一致,同时研究了在这个过程中链的形状变化情况,发现形状变化经历了四个阶段. 当聚乙烯单链的一端与吸附表面成一定倾斜角拉伸时,发现通过理想弹簧测量到的平均吸附力〈f〉与倾斜角θ在θ>20°的范围里总保持线性关系,并且其斜率随着拉伸速度的增加而增 关键词： 拉伸分子动力学 聚乙烯链 吸附现象     

Graphene Modified Lipophilically by Stearic Acid and its Composite With Low Density Polyethylene

Graphene, prepared by the thermal reduction of graphite oxide (GO), was modified with stearic acid to enhance its lipophilicity. A novel method, using the intrinsic epoxy groups on the graphene, was utilized for reaction with stearic acid to minimize the negative impact of the normal functionalization method on the π-electronic system of graphene. Gravimetric analysis, thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) showed that the stearic acid was effectively attached to the graphene. In addition, Raman spectroscopy and electric conductivity of the graphene showed that this novel modification method, utilizing intrinsic defects, did not damage the π-electronic system of the sp² bonded carbons. The dispersion of graphene in a low density polyethylene (LDPE) matrix was enhanced; consequently, the reinforcing effect in tensile testing was improved by the lipophilic modification. The crystallization behavior observed by differential scanning calorimetry (DSC) showed that the crystallization of LDPE was hindered by dispersed graphene, more evidently when dispersed uniformly.     

Interfacial reinforcement in composites with PPT aramid fiber modified by network-intercalation method

—A novel surface treatment for poly(p-phenylene telephthalamide) (PPTA) fiber is performed with silanes and urethane binder that are usually used as sizes for glass fiber treatment. The PPTA used for the surface treatment is modified by a spinning process to make the gaps between PPTA crystallites open. In this treatment, supercritical carbon dioxide fluid method is used to impregnate the sizing molecules into open gaps in PPTA fiber. After the impregnation, the fiber is heated at 100–170°C to make the gaps close and turn open-gapped fiber to the normal type of PPTA modified with sizes. The interfacial shear strength of fiber to epoxy resin is measured by microdroplet method. The modified PPTA improves the interfacial shear strength by ca. 67% to the interfacial shear strength given by normal PPTA without treatment. Those improvements are 33% without heating, 18% with only silanes, and 12% with only urethane instead of the mixture of silane and urethane. In addition, the fiber strength shows no remarkable decrease after the treatment.     

Raman polarization analysis of highly crystalline polyethylene fiber

The complex orientation dependence in space of Raman active vibrations in the orthorhombic structure of polyethylene (PE) is discussed in terms of Raman tensor elements as intrinsic physical parameters of the lattice. Building upon the symmetry assignment of these vibrational modes, we systematically studied, from both theoretical and experimental viewpoints, the changes of polarized intensity for the A_g and the B_2g + B_3g vibrational modes with respect to PE molecular orientation. After explicitly expanding the Raman selection rules associated with the A_g and the B_2g + B_3g modes, introducing them into general expressions of the orientation distribution function, and validating them by means of a least‐square fitting procedure on experimental data, we compare here two mesostructural models for a highly crystallized and self‐aligned PE fiber structure. Stereological arguments are shown concerning the arrangement of orthorhombic fibrils in such a sample that unfold the correct values of five independent Raman tensor elements for orthorhombic PE. Copyright © 2010 John Wiley & Sons, Ltd.     

Simulation analysis of ESR spectrum of polymer alkyl-C60 radicals formed by photoinitiated reactions of low-density polyethylene

Polymer alkyl-fullerene (P-C₆₀) radical adducts produced by ultraviolet (UV) photoinitiated reactions between low-density polyethylene (LDPE) and C₆₀ in the presence of benzophenone (BP) as a photoinitiator have been detected and identified for the first time by electron spin resonance (ESR) and confirmed by simulation analysis of the spectrum. A well-resolved ESR spectrum was recorded in situ upon UV irradiation of the LDPE/BP/C₆₀ sample in the molten state (413 K). Detailed analysis of hyperfine structures shows that the observed spectrum is composed of three components: a broad singlet atg = 2.0025 from the C₆₀ radical anion; an innermost pair of¹³C satellites; and a 12-line spectrum superposed on the broad singlet. The simulation analysis of the spectrum shows that the 12-line spectrum is due to the overlapping of two kinds of radical adducts of tertiary carbon-C₆₀ (A) and secondary carbon-C₆₀ (B), which have slightly differentg-values and almost the same integral intensity I_A/I_B (48.4/51.6). The spectrum simulated on the basis of the¹H and¹³C hyperfine interaction parameters is in good agreement with the observed spectrum. These results provide positive evidence that the C₆₀-bound LDPE materials can be obtained directly by a simple method of BP-photoinitiated reaction of the LDPE/C₆₀ system.     

Molecular orientation evolution during low‐density polyethylene blown film extrusion using real‐time Raman spectroscopy

Real‐time polarized Raman spectroscopy was used in this study to measure the molecular orientation evolution during blown film extrusion of low‐density polyethylene (LDPE). Spectra were obtained at different locations along the blown film line, starting from the molten state near the die and extending up to the solidified state near the nip rolls. The trans C C symmetrical stretching vibration of polyethylene (PE) at 1132 cm⁻¹ was analyzed for films possessing uniaxial symmetry. For the given peak, the principal axis of the Raman tensor is coincident with the c‐axis of the orthorhombic crystal, and was used to solve a set of intensity ratio equations to obtain second (〈P₂(cosθ)〉) and fourth (〈P₄(cosθ)〉) moments of the orientation distribution function. The orientation parameters (P₂, P₄) were found to increase along the axial distance in the film line even past the frost‐line height (FLH). The P₂ values also showed an increasing trend with crystalline evolution during extrusion, consistent with past observations that molecular orientation takes place even after the blown film diameter is locked into place. It was also found that the integral ratio (I₁₁₃₂/I₁₀₆₄) obtained from a single, ZZ‐back‐scattered mode can provide a reasonable estimate of molecular orientation. These results indicate the potential of real‐time Raman spectroscopy as a rapid microstructure monitoring tool for better process control during blown film extrusion. Copyright © 2008 John Wiley & Sons, Ltd.     

用光刺激放电法研究纳米粉末掺杂低密度聚乙烯中陷阱能级

通过光刺激放电(PSD)技术研究了纳米粉末掺杂低密度聚乙烯(LDPE)中的陷阱能级.利用连续扫描法得到了不同掺杂比例的Al₂O₃,MgO纳米粉末掺杂试样以及相同掺杂比例的多种纳米粉末掺杂试样的PSD电流谱,定性地得出了试样陷阱能级的深浅变化.分步扫描法定量地描述了LDPE试样在Al₂O₃纳米掺杂前后陷阱能量分布的变化.结果表明,掺杂比例大于0.2%的Al₂O₃纳米粉末掺杂、大于0.5%的MgO纳米粉末掺杂能够显著地使得LDPE陷阱能级变深.结合纳米掺杂对LDPE空间电荷注入影响的相关报道,可推测纳米掺杂对空间电荷注入的抑制与试样中陷阱能级变深存在密切的关联.     

Highly Active TiO2/Polyelectrolytes Hybrid Multilayered Hollow Nanofibrous Photocatalyst Prepared from Electrouspun Fibers Using Electrostatic Layer-by-Layer Technique

Compared to conventional film photocatalysts, fiber photocatalyst has a greater surface-to-volume ratio and a 3-D open structure that allows its surface active sites to be accessible for reactants more easily and effectively. However, TiO ₂ powder (Degussa P25), by itself, cannot be prepared in the form of fibers, but with the help of a polymer nanofiber, TiO ₂ particles can be immobilized in a fibrous network of polyelectrolyte. Here, hybrid multilayered hollow nanofibers (HMHNFs) composed of TiO ₂ /polyelectrolyte (PE) have been prepared by a combination of a electrospinning method and layer-by-layer (LBL) technology. The results show that both the average diameter and the wall thickness of the HMHNFs can be well controlled by the template, as well as the number of coating layers. The dried morphology of the obtained HMHNFs is dependent on the inner deposited numbers of the polyelectrolyte layers. When compared with other nanostructured TiO ₂ materials, such as commercial TiO ₂ nanoparticles (P25, Degussa) and TiO ₂ films, the hollow TiO ₂ /PE hybrid nanofibers exhibited higher photocatalytic activities.     

Electrostatic Layer-by-Layer Assembly of Hierarchical Structure of Multi-Walled Carbon Nanotubes With Glass Fiber Cloth Reinforced Epoxy Composites

A hierarchical structure of glass fiber cloth (GFC) deposited with multiwalled carbon nanotubes (MWCNTs) and cationic polyelectrolyte poly (diallyldimethylammonium chloride) (PDDA) was fabricated by the layer-by-layer (LBL) assembly method. We demonstrated that negatively charged MWCNTs, by acid functionnalization, and positively charged PDDA were sequentially adsorbed onto the GFC to form a uniform and porous interconnected network structure of MWCNTs. Multiscale composites with GFC-[PDDA-MWCNTs] _n were prepared by compression molding. The presence of the MWCNTs with their porous nanostructure helped in the formation of an interpenetrating network with the matrix at the interface layer. The resulting interlaminar strength increased by 18～37% and the surface electrical resistance (～10⁵ Ω) dropped greatly compared to those of epoxy/GFC composites (10¹⁴ Ω), showing them to be promising structural composites with GFC-[PDDA-MWCNTs] _n reinforcement with an improvement in properties over epoxy/GFC composites.     

Correlation between the birefringence and the structural parameter in photonic crystal fiber

In order to simply design a highly birefringent photonic crystal fiber (HB-PCF), we numerically simulated the correlation between the birefringence and the structural parameter of photonic crystal fiber with square-lattice or triangle-lattice air-holes by using multipole method. It is shown that the phase birefringence B(λ) and the group birefringence G(λ) can be modulated by the structure parameter of normalized wavelength λ/Λ and the relative air-hole size d/Λ. Numerical results show very high phase and group birefringence of the order of 10⁻². The group birefringence becomes negative in the region where phase birefringence increases with an increase in normalized wavelength that does not appear in traditional highly birefringent fibers.     

利用红外光谱成像技术研究PP/PE共混物

利用红外光谱对不同比例条件下制备的PP PE共混物进行了研究 ,通过对PP ,PE的特征吸收峰的分析 ,发现聚丙烯 (PP)特征峰峰面积与聚乙烯 (PE)特征峰峰面积的比值与PP/PE共混物的质量比之间存在较好的对应关系。利用特征吸收峰面积之比 ,借助红外成像技术对PP纤维热压在PE薄膜上制备的样品的研究得到了复合共混物的分布信息 ,发现其成像结果与偏光显微镜的结果有很好的吻合。实验研究结果表明采用红外成像技术 ,利用特征吸收峰面积之比可以进行对聚合物共混物的分相行为的研究。     

Adsorption of mercaptopurine drug on the BN nanotube,nanosheet and nanocluster: a density functional theory study

ABSTRACT

We have investigated the interaction of mercaptopurine (MP) drug with BN nanotube, nanosheet and nanocluster using density functional theory calculations in the gas phase, and aqueous solution. We predicted that the MP drug tends to be physically adsorbed on the surface of BN nanosheet with an adsorption energy (E_ad) about ?3.2?kcal/mol. The electronic properties of BN nanosheet are not affected by the MP drug, and this sheet is not a sensor. But the electronic properties of BN nanotube and nanocluster are significantly sensitive to this drug in both gas phase, and aqueous solution. The BN nanocluster suffers from a long recovery time (8.8?×?10⁸?s) because of a strong interaction (E_ad?=??28.6?kcal/mol), and this cluster is not a proper sensor for MP detection. But the BN nanotube benefits from a short recovery time about 49.5?s at room temperature, and may be a promising candidate for application in the MP sensors. The water solvent decreases the strength of interaction between the BN nanotube, and MP drug, but it does not affect the electronic sensitivity of the nanotube sensibly.