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1.
    
Our main objective of this study was to study the parameters affecting the free‐radical melt grafting of maleic anhydride (MA) onto linear low‐density polyethylene (LLDPE) with dicumyl peroxide (DCP) in an internal mixer. The degree of grafting (DG) was measured with titrometry and Fourier transform infrared spectroscopy. The extent of chain‐branching/crosslinking was evaluated with gel content and melt flow index measurements. The flow behavior and melt viscoelastic properties of the grafted samples were measured by using rheometric mechanical spectrometry. Feeding order, DCP and MA concentration, reaction temperature, rotor speed, and grade of LLDPE were among parameters studied. The results show that the reactant concentration (MA and DCP) played a major role in the determination of the grafting yield and the extent of the chain‐branching/crosslinking as competitive side reactions. The order of feeding also had an appreciable effect on the DG and the side reactions. Increasing the rotor speed increased the grafting yield and reduced side reactions by means of intensification of the mixing of reactants into the polyethylene (PE) melt. Chain‐branching dominated the side reactions for lower molecular weight PE, whereas for higher molecular weight PE, chain‐branching led to crosslinking and gel formation. The results of the melt viscoelastic measurements on the grafted samples provided great insight into the understanding of the role of influential parameters on the extent of side reactions and resulting changes in the molecular structure of the grafted samples. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 141–149, 2006  相似文献   

2.
    
In this work, we chemically modified linear low‐density polyethylene with maleic anhydride in the molten state using, in a first step, different doses of ultraviolet irradiation to generate hydroperoxide groups, which were highly reactive at the processing temperature. Then, in a second reactive extrusion step, maleic anhydride was grafted to the linear low‐density polyethylene under different processing conditions. Characterization of the modified and unmodified linear low‐density polyethylene material was performed with Fourier transform infrared spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

3.
    
In the present study, the properties of metallocene polyethylene–octene elastomer (POE) and wood flour (WF) blends were examined by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), an Instron mechanical tester, and scanning electron microscopy (SEM). The results showed that the mechanical properties of POE were obviously lowered, due to the poor compatibility between the two phases, when it was blended with WFs. A fine dispersion and homogeneity of WF in the polymer matrix could be obtained when acrylic acid‐grafted POE (POE‐g‐AA) was used to replace POE for manufacture of the blends. This better dispersion is due to the formation of branched and crosslinked macromolecules since the POE‐g‐AA copolymer had carboxyl groups to react with the hydroxyls. This is reflected in the mechanical and thermal properties of the blends. In comparison with a pure POE/WF blend, the increase in tensile strength at break was remarkable for the POE‐g‐AA/WF blend. The POE‐g‐AA/WF blends are more easily processed than are the POE/WF blends, since the former had a lower melt viscosity than that of the latter. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1919–1924, 2003  相似文献   

4.
    
The photografting of methacrylic acid (MAA) on a linear low‐density polyethylene film (thickness = 30 μm) under air and nitrogen atmospheres was investigated at 60°C in mixed solvents consisting of water and an organic solvent, with xanthone as a photoinitiator. The organic solvents used were acetone, methanol, tetrahydrofuran, and dioxane. A maximum percentage of grafting occurred at a certain concentration of the organic solvent in the mixed solvent. This was observed for the systems under both air and nitrogen. The grafting reaction under air exhibited an induction period, but the rate of grafting after the period was greater than that under nitrogen. The formation of poly(ethylene peroxide)s by photoirradiation seemed to be a factor for the accelerated photografting under air. On the basis of attenuated total reflection infrared spectroscopy and scanning electron microscopy of the grafted film, the MAA‐grafted chains of the sample prepared under air tended to penetrate more deeply inside the film than those of the sample prepared under nitrogen. The resulting grafted films exhibited a pH‐responsive character: the grafted films shrank in an acidic medium but swelled in alkaline medium. This was evaluated from measurements of dimensional changes in the grafted films. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 992–998, 2003  相似文献   

5.
    
The copolymerization of ethylene and 1,7‐octadiene was carried out to synthesize polyethylene with unreacted vinyl groups. The prepared copolymer [poly (ethylene‐co‐1,7‐octadiene) (PEOD)] was epoxidized with peracetic acid, m‐chloroperbenzoic acid, or formic acid/H2O2. Of these, peracetic acid gave the best results. Epoxidized PEOD was subjected to a reaction with 2‐mercaptobenzimidazole and poly(L ‐lactic acid). The bromination of PEOD was also performed in the presence of a Br2/HBr solution at room temperature. The brominated poly(ethylene‐co‐1,7‐octadiene) (PEOD‐Br) was used as a macroinitiator for atom transfer radical polymerization. The polymerization of styrene, butyl methacrylate, and glycidyl methacrylate was performed in bulk or solution at 120°C with a PEOD‐Br/CuBr/2,2′‐dipyridyl initiator system. The thermal properties of the graft copolymers and the efficiency of the graft polymerization were investigated. These graft copolymers have potential applications as interfacial modifiers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

6.
    
The effects of screw configurations, that is, the staggering angles and disc widths of the kneading blocks, on grafting reactive extrusion for maleic anhydride grafted low-density polyethylene were investigated in a corotating twin-screw extruder. Samples were collected from three positions along the screw and the die exit. The grafting degree (GD) of the specimens was evaluated by titration. It was found that the kneading block configurations had a significant influence on the grafting reactive extrusion. In addition, another three groups of extrusion experiments were performed to explore the intrinsic relationship between the GD, the degree of fill in the screw channel, the residence time distribution (RTD), and the mixing intensity in various screw configurations. The experimental results indicated that the location of the melting endpoint significantly affected the position at which the reaction began; the degree of fill, RTD, and mixing performance of the screw played important roles in the grafting reaction. The reverse kneading blocks with a narrow disc width, which had a high degree of fill and good mixing capacity, enhanced the increase in GD along the screw during the reactive extrusion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

7.
    
The effects of polyethylene‐grafted maleic anhydride (PE‐g‐MA) on the thermal properties, morphology, and tensile properties of blends of low‐density polyethylene (LDPE) and corn starch were studied with a differential scanning calorimeter (DSC), scanning electron microscope (SEM), and Instron Universal Testing Machine, respectively. Corn starch–LDPE blends with different starch content and with or without the addition of PE‐g‐MA were prepared with a lab‐scale twin‐screw extruder. The crystallization temperature of LDPE–corn starch–PE‐g‐MA blends was similar to that of pure LDPE but higher than that of LDPE–corn starch blends. The interfacial properties between corn starch and LDPE were improved after PE‐g‐MA addition, as evidenced by the structure morphology revealed by SEM. The tensile strength and elongation at break of corn starch–LDPE–PE‐g‐MA blends were greater than those of LDPE–corn starch blends, and their differences became more pronounced at higher starch contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2904–2911, 2003  相似文献   

8.
    
Glass beads were used to improve the mechanical and thermal properties of high‐density polyethylene (HDPE). HDPE/glass‐bead blends were prepared in a Brabender‐like apparatus, and this was followed by press molding. Static tensile measurements showed that the modulus of the HDPE/glass‐bead blends increased considerably with increasing glass‐bead content, whereas the yield stress remained roughly unchanged at first and then decreased slowly with increasing glass‐bead content. Izod impact tests at room temperature revealed that the impact strength changed very slowly with increasing glass‐bead content up to a critical value; thereafter, it increased sharply with increasing glass‐bead content. That is, the Izod impact strength of the blends underwent a sharp transition with increasing glass‐bead content. It was calculated that the critical interparticle distance for the HDPE/glass‐bead blends at room temperature (25°C) was 2.5 μm. Scanning electron microscopy observations indicated that the high impact strength of the HDPE/glass‐bead blends resulted from the deformation of the HDPE matrix. Dynamic mechanical analyses and thermogravimetric measurements implied that the heat resistance and heat stability of the blends tended to increase considerably with increasing glass‐bead content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2102–2107, 2003  相似文献   

9.
    
The cellular structure, physical properties, and structure–property relationships of novel open‐cell polyolefin foams produced by compression molding and based on blends of an ethylene/vinyl acetate copolymer and a low‐density polyethylene have been studied and compared with those of closed‐cell polyolefin foams of similar chemical compositions and densities and with those of open‐cell polyurethane foams. Properties such as the elastic modulus, collapse stress, energy absorbed in mechanical tests, thermal expansion, dynamic mechanical response, and acoustic absorption have been measured. The experimental results show that the cellular structure of the analyzed materials has interconnected cells due to the presence of large and small holes in the cell walls, and this structure is clearly different from the typical structure of open‐cell polyurethane foams. The open‐cell polyolefin foams under study, in comparison with closed‐cell foams of similar densities and chemical compositions, are good acoustic absorbers; they have a significant loss factor and lower compressive strength and thermal stability. The physical reasons for this macroscopic behavior are analyzed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

10.
    
The grafting of a polymer can lead to the improvement and modification of the polymer and thus expand its applications. Grafting methods include solution grafting in organic solvents, melt grafting at high temperatures, and light grafting with radioactive sources. These methods have their advantages and disadvantages. The disadvantages include waste treatment, consumption of energy, and so on. In this study, a hydrothermal process which is called the green approach, was developed to prepare graft copolymers. The effect of various factors on the grafting degree was investigated in detail. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

11.
    
The graft copolymerization of acrylic acid onto low‐density polyethylene films by simultaneous γ‐ray irradiation was carried out. The effect of water and ethanol as grafting solvents on the distribution of grafted poly (acrylic acid) in the low‐density polyethylene films was studied with optical microscopy observations of dyed and sliced samples and attenuated total reflection/Fourier infrared spectroscopy analysis. When no vigorous homopolymerization occurred, both polyethylene and poly(acrylic acid) existed in the grafted layer, and the thickness of the grafted layer and the poly(acrylic acid) concentration in the grafted layer increased with an increasing degree of grafting, regardless of the grafting conditions, the former increasing faster than the latter. In comparison with water as the solvent, in the absence of the inhibitor, homopolymerization could be suppressed to a certain degree in the ethanol solvent system, whereas in the presence of the inhibitor, obvious homopolymerization occurred at a lower monomer concentration, and both the degree of grafting and the thickness of the grafted layer were lower. Such differences could be explained by the chain transfer and the relatively low solubility of poly(acrylic acid) in ethanol. In addition, an experimental scheme using optical microscopy to observe the dyed and sliced polymers was optimized. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1570–1577, 2007  相似文献   

12.
    
CaCO3–polyethylene (PE) compositions, containing an ultrahigh molecular polyethylene (UHMPE) interlayer between the filler surface and the PE matrix, were synthesized by two‐step polymerization of ethylene on a filler surface activated with a suitable catalyst. The properties of the compositions were studied depending on the molecular weight of the PE matrix and the thickness of the UHMPE intermediate layer at the filler particles. It was shown that the presence of UHMPE as an interlayer in chalk–UHMPE–PE compositions leads to an increase of plastic deformation of the materials as long as the Mw value of the PE matrix is higher than is the brittleness threshold for PE. Chalk–UHMPE–PE compositions exhibit a higher ability for plastic deformation compared to chalk–PE compositions based on a PE matrix of a molecular weight equal to the molecular weight of the total polymer phase (UHMPE–PE) in the first case. There is no improvment of the mechanical properties when the UHMPE is dispersed in the compositions and not as an interlayer between a filler and a matrix. This means that the method of polymerization filling allows one to incorporate the polymer interlayer with a desired nature and properties between a filler surface and polymer matrix in filled polyolefin compositions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 577–583, 2003  相似文献   

13.
High‐density polyethylene (HDPE) was modified by the grafting of polydimethylsiloxane (PDMS) through a free‐radical process, in a melt‐mixer chamber, using dicumyl peroxide (DCP) as an initiator. The influence of PDMS (0.2–0.8 mol %) and peroxide (0.03–0.08 mol %) concentrations on the grafting, final torque, and melt flow rate (MFR) of copolymers were investigated using factorial planning. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), MFR, and rheometry were used to characterize the copolymers obtained. Surface plots showed that higher degrees of grafted PDMS and higher final torques were obtained with increase in the PDMS amount at low DCP levels and with increase in the DCP amount at low PDMS levels. The peaks of fusion and crystallization of the copolymers showed no significant changes with respect to HDPE. Data of MFR and GPC suggested that crosslinking reactions and/or chain extension occurred concomitant with the grafting reactions. Copolymers with high grafting degrees showed high MFR and low dynamic shear viscosities in comparison with low grafting degree copolymers, which is probably due to the migration of the PDMS‐containing copolymers on the surface. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3460–3467, 2001  相似文献   

14.
    
The photolamination of high‐density polyethylene (HDPE) by bulk photografting is described, along with a discussion of the adhesion mechanism. HDPE can be photolaminated very easily with a thin poly(acrylic acid) layer, photopolymerized from acrylic acid, with very strong adhesion obtained after a short time of UV irradiation; the adhesion failure mode is polyethylene breakage. Thicker HDPE sheets require longer irradiation times for strong adhesion. Methacrylic acid or hydroxyethyl methacrylate provides no adhesion of HDPE at all after irradiation. When glycidyl acrylate is used alone between HDPE sheets, the peel strength of the photolaminated polyethylene is only approximately 320 N/m, but when glycidyl acrylate or hydroxyethyl methacrylate is grafted with acrylic acid, very good adhesion can be obtained. It is proposed that stronger adhesion is produced by a less branched grafted chain structure, which permits much more chain entanglement. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1097–1106, 2005  相似文献   

15.
    
The thermal and mechanical properties of uncrosslinked three‐component blends of linear low‐density polyethylene (LLDPE), low‐density polyethylene (LDPE), and a hard, paraffinic Fischer–Tropsch wax were investigated. A decrease in the total crystallinity with an increase in both LDPE and wax contents was observed. It was also observed that experimental enthalpy values of LLDPE in the blends were generally higher than the theoretically expected values, whereas in the case of LDPE the theoretically expected values were higher than the experimental values. In the presence of higher wax content there was a good correlation between experimental and theoretically expected enthalpy values. The DSC results showed changes in peak temperature of melting, as well as peak width, with changing blend composition. Most of these changes are explained in terms of the preferred cocrystallization of wax with LLDPE. Young's modulus, yield stress, and stress at break decreased with increasing LDPE content, whereas elongation at yield increased. This is in line with the decreasing crystallinity and increasing amorphous content expected with increasing LDPE content. Deviations from this behavior for samples containing 10% wax and relatively low LDPE contents are explained in terms of lower tie chain fractions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1748–1755, 2005  相似文献   

16.
    
A temperature‐responsive polymer, poly(N‐isopropylacrylamide) (PNIPAAm), was grafted onto porous polyethylene membranes by a plasma‐induced graft polymerization technique. A wide range of grafting was achieved through variations in the grafting conditions, including the postpolymerization temperature, time, monomer concentration, and graft‐reaction medium. The active species induced by plasma treatment was proven to be long‐living via a postpolymerization time of 95 h. Different solvent compositions, that is, water, methanol, benzene, and water/methanol, were used as reaction media, and water showed a much higher polymerization rate than the organic solvents. Based on the hydrophilicity of the active species, a mechanism explaining the solvent effect in plasma‐induced graft polymerization was examined. Characterizations by scanning electron microscopy, X‐ray photoelectron spectroscopy (XPS), and micro Fourier transform infrared showed that the grafted polymers were located on both the outer surface and inside pores of the membranes. The XPS analysis also confirmed that the polar amide groups tended to distribute more outward when grafted PNIPAAm was in its expanding state than when it was in its shrinking state. Water permeation experiments showed that the permeability of the grafted membranes varied dramatically with a slight temperature change in the vicinity of the lower critical solution temperature (LCST) of PNIPAAm. The effective pore radii of the grafted membranes above and below the LCST could be depicted by Hagen‐Poiseuille's law. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3180–3187, 2003  相似文献   

17.
    
A thermally conductive linear low‐density polyethylene (LLDPE) composite with silicon carbide (SiC) as filler was prepared in a heat press molding. The SiC particles distributions were found to be rather uniform in matrix at both low and high filler content due to a powder mixing process employed. Differential scanning calorimeter results indicated that the SiC filler decreases the degree of crystallinity of LLDPE, and has no obvious influence on the melting temperature of LLDPE. Experimental results demonstrated that the LLDPE composites displays a high thermal conductivity of 1.48 Wm?1 K?1 and improved thermal stability at 55 wt % SiC content as compared to pure LLDPE. The surface treatment of SiC particles has a beneficial effect on improving the thermal conductivity. The dielectric constant and loss increased with SiC content, however, they still remained at relatively low levels (<102 Hz); whereas, the composites showed poorer mechanical properties as compared to pure LLDPE. In addition, combined use of small amount of alumina short fiber and SiC gave rise to improved overall properties of LLDPE composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

18.
    
The compatibility of low‐density polyethylene and poly(ethylene‐co‐vinyl acetate) containing 18 wt % vinyl acetate units (EVA‐18) was studied. For this purpose, a series of different blends containing 25, 50, or 75 wt % EVA‐18 were prepared by melt mixing with a single‐screw extruder. For each composition, three different sets of blends were prepared, which corresponded to the three different temperatures used in the metering section and the die of the extruder (140, 160, and 180°C), at a screw rotation speed of 42 rpm. Blends that contained 25 wt % EVA‐18 were also prepared through mixing at 140, 160, or 180°C but at a screw speed of 69 rpm. A study of the blends by differential scanning calorimetry showed that all the prepared blends were heterogeneous, except that containing 75 wt % EVA‐18 and prepared at 180°C. However, because of the high interfacial adhesion, a fine dispersion of the minor component in the polymer matrix was observed for all the studied blends with scanning electron microscopy. The tensile strengths and elongations at break of the blends lay between the corresponding values of the two polymers. The absence of any minimum in the mechanical properties was strong evidence that the two polymers were compatible over the whole range of composition. The thermal shrinkage of the blends at various temperatures depended mainly on the temperature and EVA‐18 content. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 841–852, 2003  相似文献   

19.
    
It is difficult to prepare polyethylene/montmorillonite by direct melt mixing because of the difference in character between polyethylene and montmorillonite. Therefore, it is necessary to modify polyethylene with polar groups, which can increase the hydrophilicity of polyethylene. At the same time, the inorganic montmorillonite should be modified with long‐chain alkyl ammonium to increase the basing space between the interlayers. Thus, through the grafting of the polar monomer onto the main chain of polyethylene by reactive extrusion, polyethylene/montmorillonite nanocomposites can be prepared by the melt mixing of the grafter and organic montmorillonite. Fourier transform infrared has been used to prove that the monomers are grafted onto polyethylene. X‐ray diffraction and transmission electron microscopy have been employed to characterize the nanocomposites. Furthermore, thermogravimetric analysis measurements show that the thermal stability of the nanocomposites is improved in comparison with that of the virgin materials. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 805–809, 2006  相似文献   

20.
    
The effects of the blend ratio, reactive compatibilization, and dynamic vulcanization on the dynamic mechanical properties of high‐density polyethylene (HDPE)/ethylene vinyl acetate (EVA) blends have been analyzed at different temperatures. The storage modulus of the blend decreases with an increase in the EVA content. The loss factor curve shows two peaks, corresponding to the transitions of HDPE and EVA, indicating the incompatibility of the blend system. Attempts have been made to correlate the observed viscoelastic properties of the blends with the blend morphology. Various composite models have been used to predict the dynamic mechanical data. The experimental values are close to those of the Halpin–Tsai model above 50 wt % EVA and close to those of the Coran model up to 50 wt % EVA in the blend. For the Takayanagi model, the theoretical value is in good agreement with the experimental value for a 70/30 HDPE/EVA blend. The area under the loss modulus/temperature curve (LA) has been analyzed with the integration method from the experimental curve and has been compared with that obtained from group contribution analysis. The LA values calculated with group contribution analysis are lower than those calculated with the integration method. The addition of a maleic‐modified polyethylene compatibilizer increases the storage modulus, loss modulus, and loss factor values of the system, and this is due to the finer dispersion of the EVA domains in the HDPE matrix upon compatibilization. For 70/30 and 50/50 blends, the addition of a maleic‐modified polyethylene compatibilizer shifts the relaxation temperature of both HDPE and EVA to a lower temperature, and this indicates increased interdiffusion of the two phases at the interface upon compatibilization. However, for a 30/70 HDPE/EVA blend, the addition of a compatibilizer does not change the relaxation temperature, and this may be due to the cocontinuous morphology of the blends. The dynamic vulcanization of the EVA phase with dicumyl peroxide results in an increase in both the storage and loss moduli of the blends. A significant increase in the relaxation temperature of EVA and a broadening of the relaxation peaks occur during dynamic vulcanization, and this indicates the increased interaction between the two phases. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2083–2099, 2003  相似文献   

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