首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
This work studied blends of PHB with epichlorohydrin elastomers, the PEP homopolymer and its copolymer with ethylene oxide, ECO. PHB is a microbial polyester, which is accumulated intracellularly by a large number of microorganisms, presenting characteristics of biodegradability and biocompatibility. It presents a high degree of crystallinity, so is a quite brittle material, and may undergo degradation when is kept for a relatively short time at a temperature above its melting point, about 180 °C. PEP and ECO are linear and amorphous elastomers, exhibit miscibility with many aliphatic polyesters and these elastomers have been used in various branches of technology, such as the automotive industry. The proposed systems combine a polymer with high crystallinity and biodegradability, PHB, with amorphous epichlorohydrin elastomers. Blends were prepared by casting from chloroform solution at different compositions (0, 20, 40, 50, 60, 80 and 100 wt% of PHB). The phase behavior of PHB/PEP and PHB/ECO blends were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and the morphology of the crystalline phase of PHB had been examined by optical microscopy. Blends of PHB/PEP and PHB/ECO have been described in literature as miscible. However, our results from the DSC and DMA show that PHB/PEP and PHB/ECO blends are immiscible. This behavior should be related to the molecular weight of polymers used in the present work, which is higher than the molecular weight of polymers used in the previous works. The crystallization kinetics of PHB is strongly influenced by the presence of the elastomeric phase. The degree of crystallinity of PHB/PEP blends decreases with an increase in the PEP content. PHB/ECO blends present degrees of crystallinity that can be considered nearly independent of the ECO content. Differences in the morphology of the crystalline phase were also observed, and these are attributed to the presence of elastomeric phase in the intraspherulitic zone.  相似文献   

2.
Polypropylene + low density polyethylene (PP + LDPE) blends involving 0, 25, 50, 75 and 100 wt% of PP with dialkyl peroxide (DAP) were prepared by melt blending in a single‐screw extruder. The effects of adding dialkyl peroxide on mechanical and thermal properties of PP + LDPE blends have been studied. It was found that at lower concentrations of peroxide (e.g., 0–0.08 wt% of dialkyl peroxide) LDPE component is cross‐linked and Polypropylene (PP) is degraded in all compositions of PP + LDPE blends. Mechanical properties (Tensile strength at break, at yield and elongation at break), Melt flow index (MFI), hardness, Scanning Electron Microscope (SEM) and thermal analyses (DSC) of these blends were examined. Because of serious degradation or cross‐linking the mechanical properties and the crystallinty (%) of those products were decreased as a result of increasing peroxide content. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

3.
Powder blends of LDPE with cellulose, ethyl cellulose, starch, chitin, and chitosan have been prepared under shear deformation in a rotor disperser at different initial-component ratios. The composition of powder fractions is identical to the original composition of the blends. The studied polymer blends demonstrate high mechanical characteristics. X-ray diffraction analysis and DSC studies show that the blending of LDPE with polysaccharides under shear deformations results in changes in the polymer structure and leads to a decrease of their degree of crystallinity. The maximum intensity of mold fungi growth is observed in starch-LDPE (50: 50, wt/wt) and chitin-LDPE (50: 50, wt/wt) blends.  相似文献   

4.
Summary PHB polyester poly(3-hydroxybutyrate) is an interesting biodegradable polymer and intensively investigated as cast and sheet films with applications in food industry or in medicine. The films obtained are typically brittle and many scientists have attempted to reduce this brittleness by blending with other polymers. PHB from Usina da Pedra was blended with PEG poly(ethyleneglycol) 300 resulting in blend 1 and blend 2. The two mixtures were melted at 200 and quenched at 0°C. TG curves showed that the thermal stability of the blends and the PHB are identical. For these blends the crystallization temperature decreased compared to the pure PHB, which is probably due to the lower nucleation density.  相似文献   

5.
Bioresource based blends exploit the synergy between polymers derived from renewable resource and commercial polymers to obtain desirable physical, mechanical, and biodegradable properties. With the aim to develop a sustainable resource based biodegradable mulch films, nanostructured blends of epoxies of linseed oil (LOE) and dehydrated castor oil (DCOE) with poly (vinyl alcohol) (PVA) were prepared in the weight ratios of 20/80, 50/50 and 80/20. Microwave-assisted blending was used for the synthesis of DCOE/LOE blends with PVA and the results were compared with conventional solution blending using FT-IR, TGA-DTA and optical measurements. The results revealed that microwave-assisted blending proved to be an efficient method for the formation of compatible blends in a short span of time as compared to conventional solution blending. Transmission electron microscopy (TEM) analysis of DCOE/PVA and LOE/PVA blends synthesized by microwave-assisted method confirmed the formation of a nanostructured blend. Scanning electron microscopy (SEM), respirometry and mechanical measurements were carried out to compare the morphology, biodegradability, and the mechanical strength of DCOE/PVA and LOE/PVA blends. It was observed that DCOE/PVA blends exhibited higher biodegradability, better mechanical properties, and lower moisture absorption characteristics as compared to LOE/PVA blends. The mechanical strength, moisture absorption, and biodegradability of these blends were also compared with blends of other bioresource based polymers such as sugarcane bagasse (SCB), waste gelation (WG), apple peal (AP), and starch/glycerol with PVA, as available from the cited literature in the text.  相似文献   

6.
Poly(vinyl alcohol) (PVA) was blended with soluble polyelectrolyte complex (PEC) made from poly(diallyldimethylammonium chloride) (PDDA) and sodium carboxymethyl cellulose (CMCNa). Crystallinity, thermal transition, and thermal stability of the PVA/PEC blends were characterized by using wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and thermal gravity analysis (TGA), respectively. Surface morphology, cross-section and phase structure of the blend membranes were examined by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). Surface hydrophilicity and swelling behavior of the blend membranes were examined by water contact angle (CA) and swelling tests. Blend membranes were subjected to isopropanol dehydration, and effects of blend composition, feed composition and feed temperature on pervaporation performance are discussed in terms of phase structures of blend membranes. A performance of J = 1.35 kg/m2 h, α = 1002, was obtained for blend membrane containing 50 wt% PEC in dehydrating 10 wt% water–isopropanol at 70 °C.  相似文献   

7.
The shape, porosity, and surface hydrophilicity of hematite particles formed from a forced hydrolysis reaction of acidic FeCl3 solution were controlled by using a trace of polymers (0.001 and 0.003 wt%). The spherical particles were produced on the systems with polyvinyl alcohol (PVA) and polyaspartic acid (PAS). In the case of polyacryl amide (PAAm), slightly small spherical particles were precipitated at 0.003 wt%. However, polyacrylic acid (PAAc) and poly-γ-glutamic acid (PGA) gave ellipsoidal particles. This morphological change on hematite particles depended on the order of functional groups of polymers as –OH<–CONH2<–COOH<–COOH and ⟩C=O, corresponding to the order in extent of polymer molecules for complexation to Fe3+ ions and adsorption onto particle surface. Accompanying this order, the hematite particles produced were changed from less porous to microporous. On the other hand, only the system with 0.003 wt% of PAAm produced mesoporous hematite particles. Choosing the kinds of polymers also controlled the ultramicroporosity and surface hydrophilicity of the particles.  相似文献   

8.
To evaluate the compatibilizing effects of isocyanate (NCO) functional group on the polyethylene terephthalate/low density polyethylene (PET/LDPE) blends, LDPE grafted with 2-hydroxyethyl methacrylate-isophorone diisocyanate (LDPE-g-HI) was prepared and blended with PET. The chemical reaction occurred during the melt blending in the PET/LDPE-g-HI blends was confirmed by the result of IR spectra. In the light of the blend morphology, the dispersions of the PET/LDPE-g-HI blends were very fine over the PET/LDPE blends. DSC thermograms indicated that PET microdispersions produced by the slow cooling of the PET/LDPE-g-HI blends were largely amorphous, with low crystallinity, due to the chemical bonding. The tensile strengths of the PET/LDPE-g-HI blends were higher than those of the PET/LDPE blends having a poor adhesion. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 447–453, 1998  相似文献   

9.
The molecular dynamics of poly(vinyl acetate), PVAc, and poly(hydroxy butyrate), PHB, as an amorphous/crystalline polymer blend has been investigated using broadband dielectric spectroscopy over wide ranges of frequency (10−2 to 105 Hz), temperature, and blend composition. Two dielectric relaxation processes were detected for pure PHB at high and low frequency ranges at a given constant temperature above the Tg. These two relaxation peaks are related to the α and α′ of the amorphous and rigid amorphous regions in the sample, respectively. The α′-relaxation process was found to be temperature and composition dependent and related to the constrained amorphous region located between adjacent lamellae inside the lamellar stacks. In addition, the α′-relaxation process behaves as a typical glass relaxation process, i.e., originated from the micro-Brownian cooperative reorientation of highly constraints polymeric segments. The α-relaxation process is related to the amorphous regions located between the lamellar crystals stacks. In the PHB/PVAc blends, only one α-relaxation process has been observed for all measured blends located in the temperature ranges between the Tg’s of the pure components. This last finding suggested that the relaxation processes of the two components are coupled together due to the small difference in the Tg’s (ΔTg = 35 °C) and the favorable thermodynamics interaction between the two polymer components and consequently less dynamic heterogeneity in the blends. The Tg’s of the blends measured by DSC were followed a linear behavior with composition indicating that the two components are miscible over the entire range of composition. The α′-relaxation process was also observed in the blends of rich PHB content up to 30 wt% PHB. The molecular dynamics of α and α′-relaxation processes were found to be greatly influenced by blending, i.e., the dielectric strength, the peak broadness, and the dielectric loss peak maximum were found to be composition dependent. The dielectric measurements also confirmed the slowing down of the crystallization process of PHB in the blends.  相似文献   

10.
Minor (<1%) macromolecular constituents may significantly affect physical/utility properties of the multicomponent polymer systems. Separation and molecular characterization of the small amounts of macromolecular additives from the dominant polymer matrices represents an exacting analytical problem. Recently a series of unconventional liquid chromatographic methods was developed for separation of the constituents of polymer blends; their generic name is Liquid chromatography under limiting conditions of enthalpic interactions, LC LC. The LC LC procedures employ the difference in elution rate of the low molecular substances and the macromolecules within the column packed with porous particles. Small molecules permeate practically all pores of the packing and therefore they elute slowly. Polymer species are partially of fully pore excluded and in absence of enthalpic interactions they are rapidly transported along the column. The appropriately chosen low molecular substances promote interactions of macromolecules within the column. If eluted in front of sample, the interaction promoting low molecular substance may create a sort of slowly eluting barrier that is “impermeable” for the interacting macromolecules and efficiently decelerates their fast transport. The blocking action of a barrier differs for macromolecules of distinct nature, which elute from the column with a different rate to be mutually separated irrespectively of their molar mass. In present work, different approaches to the LC LC separations are compared from the point of view of their applicability to complex polymer systems, in which one constituent is present at very low concentration, and also in light of sample recovery. The practical examples are the two- and three-component polymer blends of polystyrenes, poly(methyl methacrylate)s and poly(vinyl acetate)s of different molar mass averages and distributions, as well as the diblock copolymers polystyrene-block-poly(methyl methacrylate) that contain their parent homopolymers.  相似文献   

11.
In this research, an innovative Poly (vinyl alcohol) (PVA) reverse osmosis (RO) membrane with exceptional attributes was fabricated. Graphene Oxide (GO) nanosheets and Pluronic F-127 were infused within crosslinked PVA to fabricate thin film mixed matrix membranes. The newly synthesized membranes were evaluated in terms of several parameters like surface roughness, hydrophilicity, salt rejection, water permeability, Chlorine tolerance and anti-biofouling property, utilizing a dead-end RO filtration unit. Typical characterization techniques were used to assess the characteristics of the membranes. These include SEM, AFM, contact angle measurements and mechanical strength analysis. The conjugation of Pluronic F-127 and GO enhanced the overall performance of the membranes. The modified membranes surfaces had less roughness and higher hydrophilicity in comparison with the unmodified ones. This research showed that membranes that contained 0.08 wt% and 0.1 wt% GO exhibited superior selectivity, mechanical strength, Chlorine tolerance and anti-biofouling property. The truly significant outcome to evolve from this investigation is that improvements have been accomplished while PVA was used as a stand-alone RO layer without the use of any substrate. This study showed that crosslinking of PVA and modifying it with proper fillers overcame the common PVA downsides, primarily swelling and rupture under exceptionally high pressure.  相似文献   

12.
Chitosan–poly(vinyl alcohol), CS–PVA, blended membranes were prepared by solution casting of varying proportions of CS and PVA. The blend membranes were then crosslinked interfacially with trimesoyl chloride (TMC)/hexane. The physiochemical properties of the blend membranes were determined using Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), tensile test and contact angle measurements. Results from ATR-FTIR show that TMC has crosslinked the blend membranes successfully, and results of XRD and DSC show a corresponding decrease in crystallinity and increase in melting point, respectively. The crosslinked CS–PVA blend membranes also show improved mechanical strength but lower flexibility in tensile testing as compared to uncrosslinked membranes. Contact angle results show that crosslinking has decreased the surface hydrophilicity of the blend membranes. The blend membrane properties, including contact angle, melting point and tensile strength, change with a variation in the blending ratio. They appear to reach a maximum when the CS content is at 75 wt%. In general, the crosslinked blend membranes show excellent stability during the pervaporation (PV) dehydration of ethylene glycol–water mixtures (10–90 wt% EG) at different temperatures (25–70 °C). At 70 °C, for 90 wt% EG in the feed mixture, the crosslinked blend membrane with 75 wt% CS shows the highest total flux of 0.46 kg/(m2 h) and best selectivity of 986. The blending ratio of 75 wt% CS is recommended as the optimized ratio in the preparation of CS–PVA blend membranes for pervaporation dehydration of ethylene glycol.  相似文献   

13.
聚偏氟乙烯(PVDF)膜材料存在强疏水性的缺陷,亲水化改性是解决该问题的主要途径。以PVDF为基膜材料、聚乙烯醇(PVA)为共混材料、N,N-二甲基乙酰胺(DMAc)为溶剂,采用相转化法制备PVDF/PVA复合膜。考察了复合膜的PVDF/PVA共混比、固含量、低分子化合物添加剂、聚合物添加剂等非溶剂添加剂对复合膜接触角的影响。结果表明,当PVDF/PVA共混比为7/3,固含量为13%时,制备的复合膜接触角为22.92°;当添加剂为无水氯化锂、纳米二氧化硅、聚乙烯吡咯烷酮(PVP)时,复合膜接触角分别从53.12°、30.51°和41.89°都降低到了0°,亲水性提高,其中纳米二氧化硅作为添加剂时复合膜亲水性最好;当添加剂为丙三醇、PMMA、PEG时,复合膜接触角都增大,亲水性变差。  相似文献   

14.
This article describes electrically conductive polymer blends containing polyaniline‐dodecyl benzene sulfonic acid (PANI‐DBSA) dispersed in a polystyrene (PS) matrix or in crosslinked polystyrene (XPS). Melt blending of previously mixed, coagulated, and dried aqueous dispersions of PANI‐DBSA and PS latices lead to high conductivities at extremely low PANI‐DBSA concentrations (∼0.5 wt % PANI‐DBSA). In these blends, the very small size of the PANI‐DBSA particles and the surface properties (with surfactants used) of both the PANI and polymer particles play a major role in the PANI‐DBSA particle structuring process. The PANI‐DBSA behavior is characteristic of a unique colloidal polymeric filler with an extremely high surface area and a strong interaction with the matrix, evidenced by a significantly higher glass‐transition temperature of the matrix. The effect of the shear level on the conductivity and morphology of the PS/PANI‐DBSA blends was studied by the production of capillary rheometer filaments at various shear rates. An outstanding result was found for XPS/PANI‐DBSA blends prepared by the blending of aqueous XPS and PANI‐DBSA dispersions. Some of these blends were insulating at low shear levels; however, above a certain shear level, smooth surface filaments were generated, with dramatically increased and stable conductivities. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 611–621, 2001  相似文献   

15.
Miscibility and hydrogen-bonding interactions, as well as the morphological properties, of biodegradable polymer blends of poly(3-hydroxybutyrate) (PHB) and a 80% hydrolyzed poly(vinyl alcohol) (PVA80) were studied using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). It was found that PHB is miscible with PVA80 in the amorphous phase over the whole composition range. PVA80 or PHB assumes the amorphous state when its content in the blend is lower than 30 or 20 wt %, respectively. Due to the heavy overlapping of C=O stretching bands from both PVA80 and PHB and the nonmeasurable peak shift in the OH stretching band region, hydrogen-bonding interactions between the OH group of PVA80 and the C=O group of PHB were not detectable at room temperature, but were observed at a higher temperature of 180 degrees C. This is because hydrogen-bonding interactions are promoted above the melting points of these two crystalline polymers, by increasing the mixing entropy and reducing the Deltachi effect. Blending PHB with PVA80 does not have a significant effect on the OH groups of PVA80 that are hydrogen bonded with each other. Instead, the C=O groups of PHB dispossess some of the OH groups that are hydrogen bonded to the C=O groups of PVA80, which gives rise to the miscibility between PVA80 and PHB in the amorphous phase.  相似文献   

16.
Blends with varied ratio of polylactic acid (PLA) and thermoplastic polyurethane (TPU) were prepared by melt blending. The PLA content in blends was 20, 40, 60 and 80 wt%. Samples of pure PLA and TPU that underwent the same thermal treatment were also prepared. Biodegradation was examined by respirometry. Pure TPU started to degrade immediately due to degradation of the low molecular weight plasticizer in the polymer. Pure PLA, on the other hand, exhibited an incubation period after which degradation progressed rapidly and was almost complete after 70 days. The degradation profile of the blends can be correlated to their morphology. Samples with a co-continuous morphology initially degrade at a higher rate than the rest of the samples due to the higher exposure of the TPU phase in these blends.  相似文献   

17.

Ternary miscible blends based on various ratios of poly(vinyl alcohol) (PVA), poly(acrylamide) (PAM) and carboxymethyl cellulose (CMC) were prepared by solution casting in the form of thin films. The structure‐property behavior of the ternary PVA/PAM/CMC blends, before and after they had been exposed to various doses of electron beam irradiation, was investigated by FT‐IR spectroscopy, SEM, XRD and stress‐strain curves. The visual observation showed that the cast films of the individual polymers PVA, PAM, and CMC and their blends over a wide range of composition are clear and transparent indicating the miscibility of PVA/PAM/CMC ternary blends. The FT‐IR analysis of pure polymers or their ternary blends before or after electron beam irradiation proved the formation of hydrogen bonding. In addition, it was found that the intensity of the different absorption bands depends on the ratio of PAM and CMC in the ternary blend. The XRD patterns showed that the peak position for the ternary blends decreases with increasing the ratio of CMC in the blend. However, the peak position for the ternary blend based on equal ratios of pure polymers was not affected by blending and was found in the same position as in the XRD pattern of pure PVA. The SEM micrographs give support to the visual observation indicating the complete miscibility of PVA/PAM/CMC ternary blends. The improvement in morphology leads to improvement in the tensile mechanical properties of the ternary polymer blends.  相似文献   

18.
In this study, ethylene/styrene interpolymer (ESI) was used as compatibilizer for the blends of polystyrene (PS) and low‐density polyethylene (LDPE). The mechanical properties including impact, tensile properties, and morphology of the blends were investigated by means of uniaxial tension, instrumented falling‐weight impact measurements, and scanning electron microscopy. Impact measurements indicated that the impact strength of the blends increases slowly with LDPE content up to 40 wt %; thereafter, it increases sharply with increasing LDPE content. The impact energy of the LDPE‐rich blends exceeded that of pure LDPE, implying that the LDPE polymer can be further toughened by the incorporation of brittle PS minor phase in the presence of ESI. Tensile tests showed that the yield strength of the PS/LDPE/ESI blends decreases considerably with increasing LDPE content. However, the elongation at break of the blends tended to increase significantly with increasing LDPE content. The compatibilization efficiency of ESI and polystyrene‐hydrogenated butadiene‐polystyrene triblock copolymers (SEBS) for PS/LDPE 50/50 was further compared. Mechanical properties show that ESI is more effective to achieve a combination of LDPE toughness and PS rigidity than SEBS. The correlation between the impact property and morphology of the ESI‐compatibilized PS/LDPE blends is discussed. The excellent tensile ductility of the LDPE‐rich blends resulted from shield yielding of the matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2136–2146, 2007  相似文献   

19.
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  相似文献   

20.
This paper studies the structural and electrical properties of solid polymer blend electrolytes based on polyvinyl alcohol (PVA) and methylcellulose (MC) incorporated with sodium iodide (NaI). The polymer electrolyte films were assembled through a solution casting technique. The host matrix, which is doped with different NaI salt concentrations between 10 and 50 wt%, utilizes the most amorphous blend compositions (60 wt% Polyvinyl alcohol and 40 wt% methylcellulose). The structural behaviour of the electrolyte films was examined utilizing X-ray diffraction (XRD) and Fourier transformation infrared (FTIR) techniques. The semi crystalline nature of PVA:MC with inserted NaI was derived from the X-ray diffraction studies, while the XRD analysis suggests that the highest ion conductive sample displays the minimum crystalline nature. The interaction between polymer blends and inserted salt was conceived from the FTIR investigation. Shifting of peaks and variation in the intensity of FTIR bands was detected. To investigate the structural properties and calculate the degree of crystallinity of the films, the (XRD) technique was employed, while electrical impedance spectroscopy (EIS) was utilized for studying the conductivity of the samples. In order to comprehend all of the electrical properties of the ion-conducting systems, the EIS outcome of each electrolyte was matched with Equivalent Electrical Circuits (EEC) s. Ion transport parameters including mobility, carrier density and diffusion are well assessed for the samples and the dielectric properties were compared with the conductivity measurement. At lower frequencies, the dielectric constant was elevated and dielectric loss was detected. Loss tangent and electric modulus plots were used to study the relaxation nature of the samples. The highest ambient temperature conductivity of PVA loaded 50 wt% of NaI was determined to be 1.53 × 10−5 S/cm. The loss tangent relaxation peak shifts towards high-frequency side which indicates the decrease of relaxation time and faster ion dynamics.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号