Studies on the oxygen barrier and mechanical properties of low density polyethylene/organoclay nanocomposite films in the presence of ethylene vinyl acetate copolymer as a new type of compatibilizer

Nanocomposite films based on low density polyethylene (LDPE), containing of 2, 3, and 4 wt.% organoclay (OC) and ethylene vinyl acetate (EVA) copolymer as a new compatibilizer were prepared and characterized using rheological tests, X-ray diffraction, differential scanning calorimetry, oxygen permeation measurements, and tensile tests. There was no exfoliation or intercalation of the clay layers in the absence of EVA, while an obvious increase in d-spacing was observed when the samples were prepared with EVA present. This issue was reflected in the properties of nanocomposites. The oxygen barrier properties of the LDPE/EVA/OC film were significantly better than those of the LDPE/OC film. The average aspect ratio of clay platelets in nanocomposites was determined from permeability measurements and using Lape–Cussler model. In addition to barrier properties, the LDPE/EVA/OC film also had better elastic modulus than their counterparts without EVA. The modulus reinforcement of nanocomposites was studied using Halpin–Tsai equations, which are universally used for composites reinforced by flake-like or rod-like fillers.     

LDPE/EVA/蒙脱土熔融插层纳米复合体系稳态剪切流变行为

用平行板和毛细管流变仪测定并研究了具有剥离结构的低密度聚乙烯(LDPE)／乙烯-醋酸乙烯共聚物(EVA)／蒙脱土纳米复合材料熔体的稳态剪切流变行为。研究结果表明,蒙脱土含量较低的复合物熔体,在低剪切速率下,即出现剪切变稀现象；而在较高剪切速率下,填充物浓度对体系熔体的剪切粘度影响较小；与基体树脂相比较,蒙脱土的加入,使其熔体的非牛顿指数降低,粘流活化能略有增加。     

Electrical and mechanical properties of expanded graphite/high density polyethylene nanocomposites

High density polyethylene (HDPE) were filled with expanded graphite particles that have different particle sizes, 5–7 μm (EG5) and 40–55 μm (EG50) in diameter. Nanocomposites were prepared by the melt-mixing technique using EG5 and EG50 at different weight ratios. Transmission Electron Microscopy (TEM) was used to observe the morphology of the nanocomposites. X-ray diffraction patterns of EG5-HDPE and EG50-HDPE nanocomposites were investigated. Tensile tests were carried out to determine tensile strength, Young’s modulus and elongation at break values. The storage modulus and loss modulus were evaluated by Dynamic Mechanical Analysis (DMA). The effect of EG5 and EG50 on electrical conductivity of HDPE was also determined. The tensile strength of HDPE increased 18.7% and 8.5% when 40 wt% EG5 and EG50 was added into HDPE, respectively. The storage modulus of EG5-HDPE and EG50-HDPE is higher compared to that of HDPE. Incorporation of EG5 and EG10 into HDPE also increased the relaxation transition peak of HDPE. The values of electrical conductivity for EG50-HDPE nanocomposites under the same filler content obtained higher in comparison with those for EG5-HDPE nanocomposites.     

Effect of organoclay with various organic modifiers on the morphological,mechanical, and gas barrier properties of thermoplastic polyurethane/organoclay nanocomposites

Thermoplastic polyurethane (TPU)/organoclay nanocomposites are prepared through a melt extrusion process. The TPU is combined with four differently modified organoclays, namely, I.28E, I.30P, I.34TCN, and I.44P. Wide-angle X-ray diffraction and transmission electron microscopy results show that the addition of I.34TCN and I.30P to TPU/organoclay nanocomposites results in the nearly exfoliated structures of the nanocomposites. Addition of I.28E leads to partially intercalated nanocomposites, whereas I.44P cannot disperse effectively in the nanocomposites. Organoclay can enhance the mechanical and gas barrier properties of TPU. The enhancement follows the order TPU/I.34TCN ≥ TPU/I.30P > TPU/I.28E > TPU/I.44P, which is consistent with the degree of dispersion and exfoliation of silicate layers. In addition, Fourier transform infrared absorption spectra show that more hydrogen bonding sites are introduced between the clay modifiers and TPU chains in the TPU/I.34TCN and TPU/I.30P nanocomposites; this has a positive impact on the dispersion of the organoclay and, consequently, the mechanical and gas barrier properties of the nanocomposites.     

Cyclodextrin microencapsulated ammonium polyphosphate: Preparation and its performance on the thermal,flame retardancy and mechanical properties of ethylene vinyl acetate copolymer

Cyclodextrin microencapsulated ammonium polyphosphate (MCAPP) was prepared by the reaction between cyclodextrin (CD) and toluene-2,4-diisocyanate (TDI) with the goal of improving the water durability of APP and preparing a novel functional flame retardants. The Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS) results indicated MCAPP were successfully prepared, and the water contact angle (WCA) results indicated that cyclodextrin resulted in the transformation of hydrophilic to hydrophobic of the flame retardant surface. The MCAPP was then incorporated into the ethylene vinyl acetate copolymer (EVA) system and the effects of the MCAPP on the mechanical, combustion, thermal, interfacial adhesion and flame-retardant properties of EVA cable were investigated and compared by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), limiting oxygen index (LOI), mechanical test, cone calorimeter and UL-94 test. The characterization for the various properties of EVA composites demonstrated that cyclodextrin microencapsulation technology could enhance the interfacial adhesion, resulting in the improved mechanical, thermal stability, combustion properties and flame-retardant properties compared with those of EVA/APP/CD system. Furthermore, the water resistance experiments results demonstrate that EVA/MCAPP composites have good water durability due to the hydrophobic property of MCAPP. Above all, the microencapsulation of APP with cyclodextrin developed in this study may be a promising formulation for combining the acid source, the carbonization agent and the blowing agent in one flame retardant, and the MCAPP can solve the water resistance and the compatibility problem of the flame retardant during the industrial application.     

Dispersion,thermal and mechanical properties of polypropylene/magnesium hydroxide nanocomposites compatibilized by SEBS-g-MA

Isotactic polypropylene (PP)/nano-magnesium hydroxide (nano-MH) composites with 10 wt.% maleic anhydride grafted styrene–ethylene-butylene–styrene tri-block copolymer (SEBS-g-MA) as a compatilizer were prepared by melt extrusion compounding and injection molding. The effects of SEBS-g-MA on dispersion of nano-MHs in PP matrix and interfacial adhesion were studied in order to prepare highly filled PP/MH nanocomposites. The results showed that SEBS-g-MA improved both dispersion of nano-MHs and interfacial adhesion in PP/MH nanocomposites with up to 40 wt.% nano-MHs. The elastic moduli of PP/SEBS-g-MA /MH nanocomposites increased marginally and tensile yield strengths were almost invariant with nano-MH loading. Significant impact toughening of these ternary nanocomposites was, however, achieved due to the cavitation of SEBS-g-MA/MH particles and expansion of voids as well as plastic deformation of the PP matrix.     

不同蒙脱土对Al(OH)_3/乙烯-醋酸乙烯酯复合材料力学性能和阻燃性能的影响

对比研究了钙基蒙脱土(Ca-MMT)和有机改性的钠基蒙脱土(Na-MMT)对Al(OH)_3/乙烯一醋酸乙烯醋(EVA)复合材料的力学性能、热稳定性和阻燃性能的影响。采用熔融插层法制备MMT-Al(OH)_3/EVA复合材料。用XRD和TEM进行微观结构表征。结果表明:两种MMT在复合材料中均表现为一定程度的剥离分散状态,其中Ca-MMT的剥离片层相对尺寸更小。测试显示,Ca-MMT-Al(OH)_3/EVA的拉伸强度、热稳定性均高于Na-MMT-Al(OH)3/EVA;在燃烧过程中,加入Ca-MMT的Ca-MMT-Al(OH)_3/EVA复合材料热释放更低,形成的炭层隔热效果更好,表现出更优异的阻燃性能;同时火灾性能指数(FPI)提高,火灾危险性明显降低。分析原因是Ca-MMT中的Ca~(2+)在燃烧成炭中具有促进作用。     

Dynamic mechanical properties of hydroxyapatite-ethylene vinyl acetate copolymer composites

Dynamic mechanical thermal analysis (DMTA) was carried out to explore the dependence of temperature on the viscoelasticity of composites consisting of synthetic hydroxyapatite (HAP) particulate filled ethylene vinyl acetate copolymer (EVA). Two forms of HAP, differing in their surface characteristics and particle size, were used for the study. The freeze-dried HAP (FDHAP) had a mean particle size of 49.18 μm and an irregular surface morphology. In the contrary the spray dried form of HAP (SDHAP) had a mean particle size of 5.84 (m and a spherical morphology. The dynamic mechanical analysis of the composites showed that both, particle size and morphology, had a significant effect on viscoelastic properties. A tremendous increase of the storage modulus was noted with the addition of HAP. Above the T_g of the polymer matrix, the values were marginally higher for the composites containing FDHAP than for those with SDHAP. The damping (tan δ) was found to decrease with the inclusion of HAP. A marginal upper shift in the value of the glass transition temperature (T_g) was observed for the composites fabricated from SDHAP indicating a slightly strong interaction between this HAP and the EVA matrix.     

Effect of aspect ratio on thermal conductivity of high density polyethylene/multi-walled carbon nanotubes nanocomposites

This study aims to investigate experimentally the effects of aspect ratio (length/diameter ratio) and concentration of multiwalled carbon nanotubes (MWCNTs) on thermal properties of high density polyethylene (HDPE) based composites. The aspect ratios of two types of MWCNT fillers are in the range of 200–400 and 500–3000. Composite samples were prepared by melt mixing up to weight fraction of 19% filler content, followed by a compression molding. Measurements of density, specific heat and thermal diffusivity (by modulated photothermal radiometry, PTR) were performed and effective thermal conductivities k_e of nanocomposites were calculated using these values. The results show that the composites containing MWCNTs with higher aspect ratio have higher thermal conductivities than the ones with lower aspect ratio. In terms of conductivity enhancement k_e/k_m − 1, the results indicate that MWCNTs with higher aspect ratio provide three to fourfold larger enhancement than the ones with lower aspect ratio, at low filler concentrations.     

Thermal conductivity of ethylene vinyl acetate copolymer/nanofiller blends

To reduce weight and increase mobility, comfort, and performance of future spacesuits, flexible, thermally conductive fabrics and plastic tubes are needed for the Liquid Cooling and Ventilation Garment. As an approach to raise thermal conductivity (TC) of an ethylene vinyl acetate copolymer (Elvax^™ 260), it was compounded with carbon based nanofillers: multi-walled carbon nanotubes (MWCNTs), vapor grown carbon nanofibers (CNFs), and expanded graphite (EG) as well as metallized CNFs, nickel nanostrands, boron nitride, and powdered aluminum. Ribbons and tubing of the nanocomposites, in which the nanofillers were aligned in the direction of flow, were extruded. Compression molding was used to fabricate nanocomposites in which the nanofillers were randomly oriented. TC of the samples was measured in the direction of, and perpendicular to, the alignment direction and significant improvement in TC (up to 24-fold) was observed when measurements were made in the direction of alignment.     

Effect of high density polyethylene addition and testing temperature on the mechanical and morphological properties of polypropylene/ethylene-propylene diene terpolymer binary blends

High density polyethylene (HDPE) was added to the polypropylene (PP)/ethylene-propylene diene terpolymer (EPDM) binary blend, and the effect of testing temperatures on the modulus of elasticity, impact behavior and corresponding fracture morphology was analyzed. Modulus of elasticity generally decreased as the EPDM content increased regardless of the testing temperatures. However, it was found that the modulus of elasticity of PP/EPDM/HDPE ternary blend increased compared to PP/EPDM binary blend when tested at –30 and –60 °C. Notched Izod impact strength changed depending on the testing temperatures, however, there was not much difference between binary and ternary blends up to 20 wt% EPDM. However, at more than 30 wt% EPDM content, ternary blends showed higher impact strength compared to binary blends. Especially, at –30 °C, brittle-ductile transition was observed between 20 and 30 wt% EPDM. Subsurface morphology was also analyzed, and the relationship between the impact strength and the stress whitening zone was investigated. Scanning electron microscopy observation of impact fractured surfaces was conducted, and overall morphology was analyzed with respect to HDPE addition and testing temperature change.     

Influence of functionalization of multi-walled carbon nanotubes on the properties of ethylene vinyl acetate nanocomposites

Commercially available multiwalled carbon nanotubes (MWNT) were chemically modified by amine, acid and silane and their ethylene vinyl acetate (EVA) based nanocomposites were prepared. Unmodified and modified nanotubes were characterized by thermogravimetry, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. Early degradation of modified nanotubes from the thermogravimetry study proved the presence of functional groups on nanotube surface. Increase in D-band to G-band ratio and a shift in radial breathing mode peaks from the Raman spectra indicated the generation of surface defects due to functionalization and variation in van der Waals force of attraction between nanotube aggregates on modification. The unmodified nanotubes improved the tensile strength by 30% with 4 weight% of filler. Amine modification imparted further increase in strength due to the presence of functional groups on the nanotube surface and the subsequent better dispersion of the nanotubes in the polymer matrix. The silane treatment imparted maximum improvement in various properties of the nanocomposites. The nanotubes provided better thermal degradation stability and also higher thermal conductivity to virgin EVA. The results were well supported by the morphological as well as swelling study of the various samples.     

Effect of high energy ball milling on the structure and mechanical properties of cross-linked high density polyethylene

The effects of high energy ball milling (HEBM) on the structure and some key-properties of crosslinked high density polyethylene (PEX) have been thoroughly examined with a combination of X-ray diffraction analysis, IR and Raman spectroscopy, differential scanning calorimetry, gel content measurements, and tensile properties tests. A structure–property relationship, which provides a reasonable explanation for the studied case has been developed based on the experimental results and their analysis. It is proposed that the HEBM provides some of the silane-grafted macromolecular chains, which have a specific orientation, with sufficient energy in order to crosslink and form small crystalline-like areas. The arrangement of chains in the “reformed” domains leads to a total increase of the overall crystallinity, but also a decrease of the crystalline size. The proposed model can also support the fact that by increasing the milling time, the overall crystallinity of PEX and some important mechanical properties are found to increase.     

添加纳米碳管对高密度聚乙烯力学行为和结晶过程的影响

利用熔融法制备了一系列具有不同纳米碳管含量的纳米碳管(Q盯)／高密度聚乙烯(HDPE)复合材料。对其拉伸性能的研究结果表明，添加质量分数分别为2％，5％和10％的纳米碳管使HDPE的拉伸模量分别提高了7．4％，27．0％和28．6％，屈服强度分别提高了3．3％，14．4％和18．5％，但是会降低HDPE的断裂强度和断裂伸长率。同时，对复合材料中HDPE结晶过程的研究表明，纳米碳管可以提高HDPE的开始结晶温度，降低结晶活化能，但是会使HDPE的结晶速率下降，结晶度降低。     

Influence of carbon nanotube-polymeric compatibilizer masterbatches on morphological, thermal, mechanical, and tribological properties of polyethylene

Study was made of the effect of multiwall carbon nanotubes (MWCNTs) and polymeric compatibilizer on thermal, mechanical, and tribological properties of high density polyethylene (HDPE). The composites were prepared by melt mixing in two steps. Carbon nanotubes (CNTs) were melt mixed with maleic anhydride grafted polyethylene (PEgMA) as polymeric compatibilizer to produce a PEgMA-CNT masterbatch containing 20 wt% of CNTs. The masterbatch was then added to HDPE to prepare HDPE nanocomposites with CNT content of 2 or 6 wt%. The unmodified and modified (hydroxyl or amine groups) CNTs had similar effects on the properties of HDPE-PEgMA indicating that only non-covalent interactions were achieved between CNTs and matrix. According to SEM studies, single nanotubes and CNT agglomerates (size up to 1 μm) were present in all nanocomposites regardless of content or modification of CNTs. Addition of CNTs to HDPE-PEgMA increased decomposition temperature, but only slight changes were observed in crystallization temperature, crystallinity, melting temperature, and coefficient of linear thermal expansion (CLTE). Young’s modulus and tensile strength of matrix clearly increased, while elongation at break decreased. Measured values of Young’s moduli of HDPE-PEgMA-CNT composites were between the values of Young’s moduli for longitudinal (E₁₁) and transverse (E₂₂) direction predicted by Mori-Tanaka and Halpin-Tsai composite theories. Addition of CNTs to HDPE-PEgMA did not change the tribological properties of the matrix. Because of its higher crystallinity, PEgMA possessed significantly different properties from HDPE matrix: better mechanical properties, lower friction and wear, and lower CLTE in normal direction. Interestingly, the mechanical and tribological properties and CLTEs of HDPE-PEgMA-CNT composites lie between those of PEgMA and HDPE.     

Nanostructure and mechanical properties of aromatic polyamide and reactive organoclay nanocomposites

Aromatic polyamide/organoclay nanocomposites were synthesized using the solution blending technique. Treatment of montmorillonite clay with p-phenylenediamine produced reactive organophilic clay for good compatibility with the matrix. Polyamide chains were prepared by condensing a mixture of 1,4-phenylenediamine and 4-4′-oxydianiline with isophthaloyl chloride under anhydrous conditions. These chains were end capped with carbonyl chloride using 1% extra acid chloride near the end of reaction to develop the interactions with organoclay. The dispersion and structure–property relationship were monitored using FTIR, XRD, FE-SEM, TEM, DSC and tensile testing of the thin films. The structural investigations confirmed the formation of delaminated and disordered intercalated morphology with nanoclay loadings. This morphology of the nanocomposites resulted in their enhanced mechanical properties. The tensile behavior and glass transition temperature significantly augmented with increasing organoclay content showing a greater interaction between the two disparate phases.     

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.     

Effect of hybridization on the physical and mechanical properties of high density polyethylene–(pine/agave) composites

This work reports on the properties of high density polyethylene based hybrid composites made with two natural fibers: agave and pine. The composites were produced by a combination of extrusion and injection molding. The effect of hybridization was analyzed via morphological, mechanical and water immersion tests for two total fiber contents, 20 and 30 wt.%, and different pine-agave fiber ratios (100–0, 80–20, 60–40, 40–60 and 0–100). Moreover, the effect of coupling agent (maleated polyethylene) in the hybrid composite formulation was evaluated. The results showed that addition of agave fibers improves tensile, flexural and impact strength, while pine fibers decreases water uptake. As expected, the addition of a coupling agent improves substantially the quality of the polymer–fiber interface as well as the mechanical properties, but this effect was more important for composites produced with higher agave fibers content due to the their chemical composition.     

Optimization of tribological and mechanical properties of nanocomposites of polyurethane/poly(vinyl acetate)/CaCO3

Properties of samples containing polyurethane (PU), poly(vinyl acetate) (PVAc) and nanosize particles of calcium carbonate (CaCO3) are correlated with concentrations of these components. Interphase phenomena in PU/PVAc/CaCO3 nanohybrids have been studied before, we focus here on wear and scratch resistance. In addition to polymer blends containing CaCO3, the effects of adding CaCO3 with grafted PVAc, and CaCO3 with grafted silane and PVAc in varying ratios are also evaluated. For blends that do not contain the filler, a hypothesis explaining the concentration dependence of friction called the Bump Model is advanced and supported by the experimental results. In particular, we explain how creating a blend containing only 10% of a second polymer results in a dramatic drop of friction of the majority polymer. In single scratch testing, above 3% the filler displays 'its own' resistance to scratching. Chemical modification of the filler results in shallower residual depths--a consequence of improved interaction of the filler with the polymeric matrix. In sliding wear determination, strain hardening is seen for blends as well as for filler-containing composites. In tensile testing, addition of an unmodified filler increases the elongation at break and thus lowers the brittleness; the effect is even larger for chemically modified fillers.