Morphological,rheological, crystalline and mechanical properties of ethylene-vinyl acetate copolymer/linear low-density polyethylene/amphiphilic graphene oxide nanocomposites

Chemical modification of graphene oxide has become a popular method for imparting unique properties to extend its application. Here, we show a simple way to synthesize amphiphilic graphene oxide (AGO) by grafting quaternary ammonium salt onto GO sheets. The AGO sheets not only showed high thermal stability and good dispersion in many polar and non-polar solvents in comparison to GO sheets but also the chemical modification maintained the two-dimensional structure. As a result, the AGO sheets improve the interfacial interaction between ethylene-vinyl acetate copolymer (EVA) and linear low-density polyethylene (LLDPE). Because of the large size of AGO, the location of AGO is very dependent on the mixing strategy. The AGO was dispersed in the EVA phase when AGO was mixed first with EVA and then with LLDPE, whereas it was confined in the LLDPE phase when AGO was mixed first with LLDPE and then with EVA. AGO sheets were found at the interface of LLDPE and EVA when AGO, EVA, and LLDPE were mixed together, suggesting that AGO has a high interfacial interaction with both LLDPE and EVA. These high interfacial interactions lead to high tensile strength, Young's modulus, complex viscosity and crystallization temperature in comparison to the EVA/LLDPE blends without AGO sheets.     

Influence of transition metal-doped titanium(IV) dioxide on the photodegradation of polyethylene

The effects of adding dispersed powders of various forms of titanium(IV) dioxide on the photodegradation of polyethylene have been examined from the following points of view: effect of crystal form, concentration of pigment, transition metal ion, dopant concentration, calcination temperature of pigment, and pigment coating.The rate of photodegradation of polyethylene is reduced by adding certain grades of TiO₂ such as coated TiO₂ particles or TiO₂ doped with small percentages of Cr or Mn ions. The rate is increased on adding TiO₂ doped with V and especially Mo or W ions. The anatase form of TiO₂ is more photoactive than the rutile form, and the effect of increasing the calcination temperature of the pigment is to reduce photoactivity by boosting the rutile fraction. The concentration dependences of the degradation rates are complex, but can be directly related to the percentage of anatase achieved after calcination. Even the most aggressive of the metal-doped pigments are less photoactive than the Degussa P25 material, containing both rutile and anatase.     

Effect of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of intumescent flame retardant ethylene-vinyl acetate copolymer

Ethylene vinyl acetate copolymer (EVA) flame retarded by ammonium polyphosphate (APP) and pentaerythritol (PER) was cross-linked by electron beam irradiation. The effects of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of EVA composites were investigated. The volatilized products of EVA/APP/PER composites were characterized by thermogravimetric analysis/infrared spectrometry. As VA content increased, the volatilized products increased in the second decomposition step, but decreased in the third decomposition step. For all samples, the increase of irradiation dose could improve both the gel content and the Limit Oxygen Index (LOI, the minimum oxygen concentration by volume for maintaining the burning of a material) values of irradiated composites. The mechanical and thermal properties of the irradiated EVA composites were also evidently improved at appropriate irradiation dose as compared with those of unirradiated EVA composites, whereas these properties decrease at higher irradiation dose because of the electron beam irradiation-induced oxidative degradation or chain scission.     

Influence of transition metal-doped titanium(IV) dioxide on the photodegradation of polystyrene

The effects of adding dispersed powders of various forms of titanium(IV) dioxide on the photodegradation of polystyrene have been examined using FT-IR spectroscopy from the following points of view: effect of crystal form, concentration of pigment, transition metal ion, dopant concentration, calcination temperature of pigment, and pigment coating.The rate of photodegradation of polystyrene is reduced by adding certain grades of TiO₂ such as coated TiO₂ particles or TiO₂ doped with small percentages of Cr or Mn ions. The rate is increased on adding TiO₂ doped with V and especially Mo or W ions. The anatase form of TiO₂ is more photoactive than the rutile form, as is the effect of increasing the calcination temperature of the pigment. The concentration dependences of the degradation rates are complex, but can be directly related to the percentage of anatase achieved after calcination. Even the most aggressive of the metal-doped pigments are less photoactive than a Degussa P25 material, containing rutile and anatase.     

Influence of mechanical history on the crystallization behaviour and morphology of low density polyethylene

Summary If a virginal LDPE melt is sheared a memory is frozen during crystallization inasmuch as after remelting the nucleation density and the rate of crystallization are strongly increased as compared with the original material. This is not caused by the introduction of impurities into the melt during shearing.Part of this memory is recovered by annealing or solvent treatment. This reversible contribution is discussed in terms of a shear-induced increase of trans conformations in the melt, which is partly frozen on pelletizing and which becomes active again on remelting.The non-recoverable part of the memory must be due to changes of molecular structure. Since other parameters do not change it is supposed that a change of the long-chain branching frequency during shearing is the reason for the irreversible effects.Blown films produced from LDPE pellets, which originate from a strongly sheared melt and consequently have an increased crystallization rate, are known to have improved processing and end-use properties (maximum draw-down speed, optical quality). The film blowing process itself is shown to introduce an additional mechanical history into the LDPE melt such that differences of the crystallization kinetics of the starting pellets are completely equalized. A different crystallization behaviour of pellets, therefore, cannot be responsible for the differing film properties, which are more likely influenced by the different viscoelastic response of the melt.Dedicated to Professor Dr. Werner Reif on the occasion of his 60th birthday.     

On the compatibility of low density polyethylene/hydrolyzed collagen blends. II: New compatibilizers

Compatibility/compatibilization of low density polyethylene (LDPE) and hydrolyzed collagen (HC) in the presence of some reactive compatibilizing agents (CA), like acrylic acid functionalized low density polyethylene (LDPE-g-AAc) and bismaleinimide-functionalized low density polyethylene (LDPE-g-BMI) have been discussed. It has been established that, by 20-30 wt% HC incorporation in LDPE matrix, in the presence of LDPE-g-AAc and LDPE-g-BMI compatibilizing agents, materials with good mechanical and surface properties can be obtained. Because of the high reactivity of bismaleinimide, the efficacity of LDPE-g-BMI as a compatibilizing agent is higher than that of LDPE-g-AAc.     

Low density polyethylene,expanded polystyrene and expanded polypropylene: Strain rate and size effects on mechanical properties

Polymeric foam materials may be used as energy absorbing materials for protection in impact scenarios, and design with these materials requires the mechanical properties of foams across a range of deformation rates, where high deformation rate testing often requires small samples for testing. Owing to their cellular macrostructure, and the large deformations that occur during loading of foams, the measured stress-strain response of a foam material may be influenced by the sample size. In this study, the mechanical properties of three closed-cell polymeric foams (Low Density Polyethylene, Expanded Polystyrene and Expanded Polypropylene) at two different densities were investigated over a range of deformation rates from 0.01 s⁻¹ to 100 s⁻¹. For each foam material, three different nominal sample sizes (10 mm, 17 mm and 35 mm) were tested. On average, the polymeric foam materials exhibited increasing stress with increasing deformation rate, for a given amount of strain.Density variation was identified at the sample level, with smaller samples often exhibiting lower density. Expanded Polystyrene demonstrated the highest variability in sample density and corresponding variability in mechanical response, qualitatively supported by observed variations in the macrostructure of the foam. Expanded Polypropylene exhibited variability in density with sample size, and observable variability in the material macrostructure; however, the dependence of the measured mechanical properties on sample size was modest. Low Density Polyethylene was found to have a relatively consistent cell size at the macrostructure level, and the material density did not vary significantly with sample size. In a similar manner, the dependence of measured mechanical properties on sample size was modest. The effect of sample size was identified to be material specific, and it is recommended that this be assessed using sample-specific density measurements and considering different sized samples when testing foam materials.     

Effect of organoclay loading and electron beam irradiation on the physico‐mechanical properties of low‐density polyethylene/ethylene‐vinyl acetate blend

The influence of electron beam (EB) irradiation and organoclay (OC) loading on the properties of low‐density polyethylene (LDPE)/ethylene‐vinyl acetate (EVA) blends was investigated. The samples were subjected to the EB irradiation with the dose values of 50 and 250 kGy. X‐ray diffraction (XRD), gel content, mechanical, thermal, and electrical properties were utilized to analyze the characteristics of the LDPE/EVA blends with and without OC at different irradiation dosages. Gel content analysis showed that the OC promotes considerably the insoluble part so that the LDPE/EVA blends filled with OC become fully crosslinked at 250 kGy; possibly through the formation of further crosslinks between OC and polymer chains. The samples irradiated by EB showed enhanced mechanical properties due to the formation of three‐dimensional networks. In addition, thermogravimetric analysis indicated that combined OC loading and radiation‐induced crosslinking improved thermal stability of LDPE/EVA blends considerably. Copyright © 2011 John Wiley & Sons, Ltd.     

Transition metal-doped titanium(IV) dioxide: Characterisation and influence on photodegradation of poly(vinyl chloride)

The effects of transition metal dopants (V(IV), V(V), Mn(II), Cr(III), Mo(V), and W(V)), introduced into TiO₂, upon the rate of photodegradation of poly(vinyl chloride) (PVC) films containing TiO₂ have been measured. The rates were determined mainly by monitoring carbonyl group formation. In another set of experiments, the rates of chloride ion release from irradiated PVC particles suspended in water undergoing agitation with air or O₂ in the presence of particles of doped TiO₂ were measured electrochemically. The doping of TiO₂ (rutile) with Cr(III), V(V) or Mn(II) reduces the photoactivity of the pigment, while doping by Mo(V) or W(V) enhances its photoactivity; the results obtained from carbonyl index measurements are paralleled closely by those from chloride ion release. Even the most aggressive doped pigments were less reactive than Degussa P25 pigment, while the greatest protection to PVC film was offered by TiO₂ particles coated with Al₂O₃ or SiO₂. Overall, the photoactivity of doped TiO₂ is a complex function of dopant concentration, the energy levels of the dopants in the TiO₂ lattice, their d electronic configuration and their local distribution. Photoactivity is also linked to other factors such as crystal type, particle size distribution and surface area. There is a clear relationship between the tendency of the dopant to induce the rutile-to-anatase transition and its effect in enhancing the photoactivity of the pigment. The characterisation of the doped pigments was achieved using X-ray powder diffraction, EPR spectroscopy, diffuse reflectance UV-vis spectrophotometry, scanning optical and electron microscopy and particle size analysis using LALLS.     

A novel zinc chelate complex containing both phosphorus and nitrogen for improving the flame retardancy of low density polyethylene

A novel metal chelate complex containing phosphorus, nitrogen and zinc (II) ion was synthesized and used as the flame retardant of low density polyethylene (LDPE). The zinc chelate complex was synthesized by reacting zinc acetate with the ligand of tetraethyl (1,2-phenylenebis(azanediyl)) bis (2-hydroxylphenylmethylene) diphosphonate (TEPAPM). The chemical structure of the target Zn-TEPAPM was confirmed by FTIR, ¹H NMR, ¹³C NMR and ³¹P NMR spectra. The flame retardancy and thermal behavior of LDPE containing various amount of Zn-TEPAPM were investigated by limiting oxygen index test, thermogravimetric (TG) analysis and cone calorimetry. The results show that Zn-TEPAPM can greatly increase the thermal stability, the char formation and smoke suppression ability of LDPE. The TG curves show that even when the filler content of Zn-TEPAPM is as low as 1 wt% in LDPE, the onset degradation temperature of LDPE is increased from 429 °C to 442 °C, and the maximum degradation temperature is increased from 469 °C to 488 °C. Also, a reduction of 32% for the peak heat release rate (PHRR) is obtained in the cone test. Moreover, Zn-TEPAPM is demonstrated to be a very effective synergist of ammonium polyphosphate (APP). When 1 wt% of Zn-TEPAPM was introduced into the LDPE/APP (mass ratio 80/19) blend, the PHRR value is reduced by 32%, compared with that of LDPE/APP blend without Zn-TEPAPM, and the char layer becomes more compact and intact.     

水溶性聚合物和两亲聚合物

研究了晶种存在下，丙烯酸／乙酸乙烯酯无规共聚物对二水合硫酸钙从过饱和水溶液中结晶动力学的影响。发现该共聚物存在下ＣａＳＯ４·２Ｈ２Ｏ的结晶过程存在诱导期。诱导期随共聚物浓度或共聚物中乙酸乙烯酯含量的增加而增加，随温度、晶种含量或初始钙离子浓度的降低而增加。诱导期后的结晶生长速度与共聚物浓度、共聚物组成和晶种用量几乎无关。     

Effect of oscillatory shear on the mechanical properties and crystalline morphology of linear low density polyethylene

In this study,effects of oscillatory shear with different frequencies(0-2.5 Hz) and amplitudes(0-20 mm) on the mechanical properties and crystalline morphology of linear low density polyethylene(LLDPE) were investigated.It was found that the mechanical properties of LLDPE are improved because of the more perfect crystalline structure when LLDPE crystallizes under low-frequency and small-amplitude(0.2 Hz/4 mm) oscillatory shear.The mechanical properties can be further improved by increasing either the frequency or the amplitude of oscillatory shear.The Young's modulus and tensile strength of LLDPE are improved by 27% and 20%,respectively,when the frequency is increased to 2.5 Hz and the amplitude is maintained at 4 mm; while the Young's modulus and tensile strength are improved by 49% and 47%,respectively,when the amplitude is increased to 20 mm and the frequency is remained as 0.2 Hz.The crystallinity and microstructure of LLDPE under different oscillatory shear conditions were investigated by using differential scanning calorimetry,wide angle X-ray diffraction and scanning electron microscopy to shed light on the mechanism for the improvement of mechanical properties.     

Effect of ethylene-acrylic acid copolymer on flame retardancy and properties of LLDPE/EAA/MH composites

Halogen-free flame retardant linear low density polyethylene (LLDPE)/ethylene-acrylic acid copolymer (EAA) blends were prepared in a melt process using magnesium hydroxide (MH) as flame retardant. The effect of EAA on flame retardancy and properties of LLDPE/EAA/MH composites was studied. The flammability of composites was investigated using Limiting Oxygen Index (LOI) and Cone calorimeter test. The results showed that the introduction of EAA into composites apparently increased LOI from 28% to 39%, meanwhile, reduced heat release rate (HRR) and smoke production rate (SPR) according to Cone calorimeter results, which was mainly due to the uniform dispersion of MH as a result of hydrogen bonding and acid-base reaction between MH and EAA. This improved interfacial adhesion was confirmed by Scanning Electronic Microscopy (SEM). Thermogravimetric analysis (TGA) showed that EAA could enhance the thermal oxidative stability of composites. It was attributed to the formation of a stable barrier to prevent the heat and mass transfer in fire, which was confirmed by the observation of fire performance with Cone calorimeter. The crystallization and rheological behaviour of composites were studied using Differential scanning calorimeter (DSC) and oscillatory rheological measurements. Mechanical test results indicated that the addition of EAA could increase the elongation at break and impact strength of composites.     

Preparation of high density polyethylene/polyethylene-block-poly(ethylene glycol) copolymer blend porous membranes via thermally induced phase separation process and their properties

<正>High density polyethylene(HDPE)/polyethylene-block-poly(ethylene glycol)(PE-b-PEG) blend porous membranes were prepared via thermally induced phase separation(TIPS) process using diphenyl ether(DPE) as diluent.The phase diagrams of HDPE/PE-b-PEG/DPE systems were determined by optical microscopy and differential scanning calorimetry(DSC).By varying the content of PE-b-PEG,the effects of PE-b-PEG copolymer on morphology and crystalline structure of membranes were studied by scanning electron microscopy(SEM) and wide angle X-ray diffraction(WAXD). The chemical compositions of whole membranes and surface layers were characterized by elementary analysis,Fourier transform infrared spectroscopy-attenuated total reflection(FTIR-ATR) and X-ray photoelectron spectroscopy(XPS).Water contact angle,static protein adsorption and water flux experiments were used to evaluate the hydrophilicity,antifouling and water permeation properties of the membranes.It was found that the addition of PE-b-PEG increased the pore size of the obtained blend membranes.In the investigated range of PE-b-PEG content,the PEG blocks could not aggregate into obviously separated domains in membrane matrix.More importantly,PE-b-PEG could not only be retained stably in the membrane matrix during membrane formation,but also enrich at the membrane surface layer.Such stability and surface enrichment of PE-b-PEG endowed the blend membranes with improved hydrophilicity,protein absorption resistance and water permeation properties,which would be substantially beneficial to HDPE membranes for water treatment application.     

Rheological investigation of the influence of molecular structure on natural and accelerated UV degradation of linear low density polyethylene

Metallocene and Ziegler-Natta (ZN) linear low density polyethylenes (LLDPEs) of different branch types and contents as well as linear high density polyethylene (HDPE) were exposed to natural and accelerated weather conditions. The degree of UV degradation of exposed samples was measured by rheological techniques and results were compared with unexposed polymers. Dynamic shear measurements were performed in an ARES rheometer in the linear viscoelastic range. The degree of enhancement or reduction in viscosity and elasticity was used as a measure of the degree of cross-linking or chain scission, respectively. The degradation results of LLDPE suggest that both cross-linking and chain scission are taking place. Chain scission dominated the degradation at high levels of short chain branching (SCB) and long exposure times. The degradation mechanism of m-LLDPE and ZN-LLDPE is similar; however, m-LLDPE showed a higher degradation rate than ZN-LLDPE of similar M_w and average SCB. ZN-LLDPE was found to be more stable than a similar m-LLDPE. Comonomer type had little influence on degradation. Dynamic shear rheology was very useful in revealing the influence of different molecular parameters and it exposed the degradation mechanism.     

Electrically conductive,melt‐processed ternary blends of polyaniline/dodecylbenzene sulfonic acid,ethylene/vinyl acetate,and low‐density polyethylene

Although polyaniline (PANI) has high conductivity and relatively good environmental and thermal stability and is easily synthesized, the intractability of this intrinsically conducting polymer with a melting procedure prevents extensive applications. This work was designed to process PANI with a melting blend method with current thermoplastic polymers. PANI in an emeraldine base form was plasticized and doped with dodecylbenzene sulfonic acid (DBSA) to prepare a conductive complex (PANI–DBSA). PANI–DBSA, low‐density polyethylene (LDPE), and an ethylene/vinyl acetate copolymer (EVA) were blended in a twin‐rotor mixer. The blending procedure was monitored, including the changes in the temperature, torque moment, and work. As expected, the conductivity of ternary PANI–DBSA/LDPE/EVA was higher by one order of magnitude than that of binary PANI–DBSA/LDPE, and this was attributed to the PANI–DBSA phase being preferentially located in the EVA phase. An investigation of the morphology of the polymer blends with high‐resolution optical microscopy indicated that PANI–DBSA formed a conducting network at a high concentration of PANI–DBSA. The thermal and crystalline properties of the polymer blends were measured with differential scanning calorimetry. The mechanical properties were also measured. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3750–3758, 2004     

Effect of the content of urea groups on the particle size in water-borne polyurethane or polyurethane/polyacrylate dispersions

A series of anionic water-borne polyurethane and polyurethane/polyacrylate dispersions and their paint films was prepared. It was found by using TEM that there were three phases in the polyurethane/polyacrylate film, i.e. the hard segment-rich phase and the soft segment-rich phase of polyurethane, and the polyacrylate phase. By increasing the content of urea groups, the glass transition temperature of the soft segments and the dissociation temperature of the long-distance ordering of the hard segments were raised. This should mean that the motion of macromolecular chains was hindered by increasing the content of urea groups, and the hydrophilic carboxyl groups embedded initially in macromolecular coils could thus not transfer easily to the particle surface, which resulted in a greater average particle size in the dispersion.     

Effect of biodegradation conditions on morphology of ternary compositions of low density polyethylene with poly(lactic acid) and starch

Polyethylene–poly(lactic acid)–starch ternary compositions were obtained in a rotor disperser under conditions of shear deformation. Their biodegradation under the action of mold fungus spores and soil was investigated using IR spectroscopy and SEM. The changes under the fungal action revealed that the ternary blends represented a nutrient medium, while the exposure to soil led to alteration in morphology due to the whole range of numerous environmental factors.     

Effect of equal channel angular pressing on thermal and mechanical properties of carbon nanotube/high density polyethylene composite

High density polyethylene (HDPE) nanocomposite reinforced with 2 weight percent carbon nanotube (CNT) was fabricated using mechanical milling method. Microscopic evaluations revealed appropriate dispersion of CNTs in the matrix, and tensile tests demonstrated that the tensile strength was increased by 17%. Thermal and mechanical properties of the composite samples were investigated after equal channel angular pressing (ECAP) for up to 3 passes via route A at temperature of 80°C. Density and differential scanning calorimetry (DSC) results represented decrement in crystallinity after ECAP which was led to drop in hardness and tensile yield strength of the deformed samples. Micro Vickers and Shore D hardness results also revealed clear anisotropy in mechanical properties caused by ECAP. Dilatometry results and observation of the impact fractured surfaces of deformed samples demonstrated that oriented structures formed in amorphous and crystalline regions of the composite. This microstructure evolution also caused increase in impact strength of ECAP deformed specimens. Dynamic mechanical behavior of the processed samples was modified following ECAP. The α and γ relaxation temperatures were decreased due to the reduction of thickness of crystalline lamella obtained from DSC results, in 1 pass ECAP deformed sample. Dynamic storage and loss modulus of 3 passes ECAP deformed samples were significantly decreased due to the sharp drop in their crystallinity.     

Effect of annealing on the viscoelastic and viscoplastic responses of low‐density polyethylene

Two series of tensile tests with constant crosshead speeds (ranging from 5 to 200 mm/min) and tensile relaxation tests (at strains from 0.03 to 0.09) were performed on low‐density polyethylene in the subyield region of deformations at room temperature. Mechanical tests were carried out on nonannealed specimens and on samples annealed for 24 h at the temperatures T = 50, 60, 70, 80, and 100 °C. Constitutive equations were derived for the time‐dependent response of semicrystalline polymers at isothermal deformations with small strains. A polymer is treated as an equivalent heterogeneous network of chains bridged by temporary junctions (entanglements, physical crosslinks, and lamellar blocks). The network is thought of as an ensemble of mesoregions linked with each other. The viscoelastic behavior of a polymer is modeled as a thermally induced rearrangement of strands (separation of active strands from temporary junctions and merging of dangling strands with the network). The viscoplastic response reflects sliding of junctions in the network with respect to their reference positions driven by macrostrains. Stress‐strain relations involve five material constants that were found by fitting the observations. Fair agreement was demonstrated between the experimental data and the results of numerical simulation. This study focuses on the effects of strain rate and annealing temperature on the adjustable parameters in the constitutive equations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1638–1655, 2003