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1.
Composite nucleating agent (CNA) consisting of zinc oxide as a crystallization promoter and phenylphosphonic acid zinc salt (PPZn) as an heterogeneous nucleation agent was employed to improve the crystallization behaviors of branched poly (lactic acid) (B-PLA) which was prepared by use of multi-functional epoxy-based chain extender (CE). The differential scanning calorimeter results showed that the crystallinity and crystallization temperature of prepared B-PLA/CNA were higher than that of linear poly (lactic acid) (L-PLA) and B-PLA at a high cooling rate. The corresponding phenomena of heterogeneous nucleation of B-PLA/CNA were observed by means of polarized optical microscope. The crystalline mechanism research results show that the degradation reaction and chain extending reaction were occurred simultaneously after the addition of CE and CNA into the PLA, PPZn as an effective nucleation points could increase the nucleation density and the degraded short molecular chains with higher chain mobility would improve crystal growth during the crystallization of the branched PLA. Non-isothermal cold crystallization kinetics of various B-PLA with different content of CNA was studied. The corresponding result showed that the crystallinity and crystallization rate increased obviously with the CNA content greater than or equal to 5phr, as well as the crystallization time decreased. The similar experimental results of non-isothermal and isothermal melt crystallization kinetics also showed that CNA had a significant impact on crystallization behavior of B-PLA.  相似文献   

2.
Polyvinyl alcohol (PVA) and starch are both biodegradable polymers. These two polymers can be prepared as biodegradable plastics that are emerging as one of the environmental friendly materials available now. In this study, after reacting with sodium trimetaphosphate (STMP), modified corn starch was blended with PVA in different ratios by a barbender. Test samples were prepared for mechanical and thermal properties measurements. The surface roughness and morphology of fractured surface of the samples were observed by an atomic force microscopy (AFM) and scanning electron microscope (SEM) measurements. Aqueous degradation by enzyme, water absorption and biodegradability behavior were evaluated for the degradability. The biodegradability of these materials was followed by bio-reactivity kinetics models. Results showed that the addition of modified starch could enhance its water uptake. With an addition of 20 wt% of modified starch, the blend had a maximum weight loss during enzymatic degradation. It was found that the degradability was enhanced with the addition of the starch. Analyzing the results of the biodegradability based on the kinetic models, the growth rate of the microorganism was found to be increasing with the increase of the content of starch in the PVA/starch blends in the first order reaction fashion. In our biodegradability analysis, i.e., based on the China national standards (CNS) 14432 regulations, we estimated the decomposition behavior based on the mentioned first order reaction. We found that the PVA/starch blends would take 32.47, 16.20 and 12.47 years to degrade by 70% as their starch content 0, 20 and 40 wt%, respectively.  相似文献   

3.
Low-density polyethylene (LDPE) was employed to improve the thermal and rheological properties as well as the supercritical CO2 foaming behavior of poly(lactic acid) (PLA) through melt mixing and batch foaming method, due to its long branched chain structure, moderate crystallization capacity and good foamability. The differential scanning calorimetry and polarized optical microscope results showed that the introduction of LDPE had a slight effect for promoting the crystallization of PLA. An important synergistic effect on the rheological properties of PLA/LDPE blends was found through rotational rheometer. With the content of LDPE, the size of spherical LDPE dispersion phase became bigger gradually, which was observed by scanning electron microscope (SEM). A very interesting cellular morphology evolution from flower-like cellular structure to complex cellular structure and then to mono-porous cell structure was found in the SEM images of the PLA/LDPE blending foams with the foaming temperature at 95 °C. The effect of blending ratio and foaming temperature on the cellular morphology and foaming parameters was investigated.  相似文献   

4.
Poly(lactic acid) (PLA) has gained considerable attention nowadays as a biocompatible polymer owing to its advantage of being prepared from renewable resources. PLA exhibits excellent tensile strength, fabricability, thermal plasticity and biocompatibility properties comparable to many petroleum based plastics. However, low heat distortion temperature, brittleness and slow crystallization rate limit the practical applications of PLA. In order to address these limitations, an attempt has been made in the current work to prepare binary blends of PLA with ethylene vinyl acetate (EVA) at different compositions via melt mixing technique. Systematic investigation on the mechanical properties, thermal degradation and crystallization behavior for PLA-EVA blends was carried out. The impact strength of binary blends of PLA–EVA was found to increase significantly by 176% for 15 wt% of EVA compared to virgin PLA. This is due to the strong interfacial adhesion among PLA and EVA resulting in brittle to ductile transition. Scanning electron microscopy analysis for impact fractured surfaces of binary blends of PLA implied the toughening effect of PLA by EVA. Thermogravimetry analysis results revealed that the activation energy of PLA–EVA blends decreased with increase in EVA content in the PLA matrix. While, differential scanning calorimetry results obtained for PLA–EVA blends revealed the improvement in crystallinity when compared with neat PLA. The effect of EVA on non-isothermal melt crystallization kinetics of PLA was also examined via DSC at various heating rates. Decreasing trend in the t1/2 values indicated the faster rate of crystallization mechanism after addition of EVA in the PLA matrix.  相似文献   

5.
The melting and crystallization behavior of pure poly (lactic acid) (PLA) and PLA composites (1% Bamboo Fiber (BF)/PLA, 1% Talc/PLA, 1% BF/1% Talc/PLA) were studied with differential scanning calorimetry (DSC). DSC curves for PLA composites were obtained at various cooling rates, the crystallization temperature and heat of crystallization of PLA composites decreased almost linearly with increasing of log (cooling rate). Moreover, BF has minor effect and talc has the great effect on the crystallization temperature in the PLA composites. With increasing of cooling rate, the main melting temperature of PLA composites decreased. In pure PLA and 1% BF/PLA, the double-melting behavior appeared in the heating curves after slow rate of cooling, and there was the opposite phenomenon of double-melting behavior in other two PLA composites. BF promotes forming the imperfect crystal in the PLA composites during heating process. With increasing of heating rate, the main melting temperature of PLA composites increased except the 1% BF/PLA. At various heating rates, the defects of BF structure promoted the melt-recrystallization and talc promoted forming the small crystals. At last, the recrystallization model was given.  相似文献   

6.
Several starch/PVA/glycerol polymer blends were prepared by a solution casting technique and examined for biodegradation by composting over 45 days. Within this time frame, the starch and glycerol components were fully degraded, leaving the PVA component essentially intact. The lowest PVA content film (20%) was selected as a polymer with enough PVA to impart important physical characteristics, but also enough starch to be considered biodegradable. The film characteristics were further improved by surface modification with chitosan. This modification did not interfere with the biodegradation of the starch component. Furthermore, there was slight evidence that PVA biodegradation had been initiated in composted, surface modified starch/PVA blends.  相似文献   

7.
Fully-biodegradable and highly-filled thermoplastic starch plasticized with glycerol (GTPS)/poly (butylene succinate) (PBS) blends were prepared by Haake Mixer. Processing properties, thermal behaviors including melting and crystallization behavior, crystal structure, and compatibility of the blends were investigated using differential scanning calorimeter (DSC), wide angle X-ray diffractometer (WAXD), scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA). The maximum and equilibrium torques decreased with the rising of glycerol contents and the dropping of PBS contents. GTPS30/PBS blends exhibited double melting endothermic peaks in the DSC thermograms, which related to the crystallization behavior and compatibility of the blends, but no double peaks for GTPS40/PBS. The addition of starch and glycerol could lead to higher crystallinity and lower crystallization rate of PBS, but would not change the crystal types and crystallite sizes of PBS according to DSC and WAXD analysis. SEM and DMA results gave the evidence to confirm the better compatibility of GTPS40/PBS. Besides, higher storage modulus in glassy state of GTPS/PBS blends than PBS could be seen from DMA analysis, which was the contrary in rubbery state.  相似文献   

8.
The common biodegradable properties of polymer make them an excellent pair for blending, and the water solubility of polyvinyl alcohol (PVA) makes it easy to mix evenly with the starch. In this study, PVAs with different molecular weights were blended with various compositions of cross-linked starch (CLS) to explore the effects of molecular weight of PVA on the biodegradable characteristics of the PVA/starch blends. Comparing the biodegradability of all the various PVA/starch blends, a PVA was singled out from the PVA/starch blends of higher biodegradability. Further, the chosen PVA was then blended with the acid-modified starch (AMS) to systematically investigate the effects of the modified processing of starch on the biodegradable characteristics of the PVA/starch blends. Differential scanning calorimetry (DSC) analysis of PVA and PVA/starch specimens reveal that the Tm values of PVA/starch specimens reduce gradually as their CLS or AMS contents increase. After the CLS is blended in PVAs of different molecular weights, the tensile strength (??f) and elongation at break (??f) values of (P100S0)G20M1 specimen increase and simultaneously reduce, respectively, as their molecular weights of PVA increase from about 80,000 (PVABF-17) to 120,000 (PVABF-26). The ??f and ??f values of the PVA/modified-starch blends decrease with an increase in the modified starch contents. The ??f values of the PVA/AMS specimens decrease with an increase in the concentrations of hydrochloric acid. Comparing the ??f values of the PVA/CLS specimens with those of the PVA/AMS specimens, the ??f values of the PVA/CLS specimens are better than those of the PVA/AMS specimens. On the contrary, the ??f values of the PVA/AMS specimens are better than those of the PVA/CLS specimens. According to the biodegradability of all the PVA/starch blends, PVA with higher molecular weights displays higher biodegradability. The biodegradability of the PVA/modified-starch blends increase as the modified starch contents of the PVA/modified-starch blends increase. As evidenced by the results of the biodegradability test, the biodegradability of the PVA/modified-starch blends, therein PVA is blended with 1N AMS, shows better biodegradability. The result of bio-reaction kinetics experiment can evaluate the decomposition tendency of the PVA/starch blends up to any biodegradable rate under ambient environment. Using the kinetic model of the first order reaction, it is estimated that 16.20?years and 12.47?years will be needed for the PVABF-17/starch blends, containing 20 and 40% of CLS respectively, to be degraded up to 70% under ambient environment. In addition, it is 1.68?years for the PVABF-26 blends with the 40% 2N AMS under decomposition environment while it is 1.94?years for the 40% 1N AMS. Overall, the decomposition potential of PVA/AMS specimens is better than PVA/CLS specimens. Furthermore, the 1N(26P60AS40)100G20M1 specimen is coincidence the biodegradable material criteria of Environmental Protection Administration (EPA) of Taiwan.  相似文献   

9.
Two biodegradable polyesters, poly(butylene adipate-co-terephthalate) (PBAT) and poly(butylene succinate) (PBS) were melt-compounded in a twin screw extruder to fabricate a novel PBS/PBAT blend. The compatibility of the blend was attributed to the transesterification reaction that was confirmed by Fourier transform infrared spectroscopy. The Gibbs free energy equation was applied to explain the miscibility of the resulting blend. Dynamic mechanical analysis of the blends exhibits an intermediate tanδ peak compared to the individual components which suggests that the blend achieved compatibility. One of the key findings is that the tensile strength of the optimized blend is higher than each of the blended partner. Rheological properties revealed a strong shear-thinning tendency of the blend by the addition of PBAT into PBS. The phase morphology of the blends was observed through scanning electron microscopy, which revealed that phase separation occurred in the blends. The spherulite growth in the blends was highly influenced by the crystallization temperature and composition. In addition, the presence of a dispersed amorphous phase was found to be a hindrance to the spherulite growth, which was confirmed by polarizing optical microscopy. Furthermore, the increased crystallization ability of PBAT in the blend systems gives the blend a balanced thermal resistance property.  相似文献   

10.
Nucleation of polylactide and polypropylene using novel renewable resource biobased carbon nanospheres (CNS) is investigated using differential scanning calorimetry and polarized optical microscopy. Isothermal studies near the optimal crystallization temperature demonstrate at least a five-fold increase in crystallization rate in PP but only a 1.4 times faster crystallization in PLA. Non-isothermal studies reveal an asymptotic relationship of the maximum crystallization temperature with increasing CNS weight loading in PP and no relationship in PLA. Microscopy indicates some aggregation in the solution blended samples and that average spherulite size is reduced 10-fold due to faster nucleation in the composites as compared to the neat polymer. The fractional crystallinity achieved during non-isothermal crystallization increases by about 7% with addition of a small amount of CNS and decreases with weight loading higher than 1%. The crystallization rates obtained in polypropylene are competitive with widely used mineral talc nucleating agents.  相似文献   

11.
Blends of water—soluble polymers based on Poly vinyl alcohol (PVA) and Polyethylene glycol (PEG) have been prepared by the solution casting technique. The effect of various doses of γ-radiation on the structural properties of PVA/PEG polymer blends with all its compositions has been investigated. From the visual observation of all the blend compositions, it was found that, the best compatibility of the blend is up to 40% PVA/60%PEG. The structure–Property behavior of all the prepared blends before and after γ-irradiation was investigated by IR Spectroscopy, thermogravimetric analysis (TGA), mechanical properties and Scanning electron microscope (SEM). The gel content and the swelling behavior of the PVA/PEG blends were investigated. It was found that the gel content increases with increasing irradiation dose and PVA concentration in the blend. Swelling percent increased as the composition of PEG increased in the blend. The results obtained by FTIR analysis and SEM confirm the existence of possible interaction between PVA and PEG homopolymers. TGA of PVA/PEG blend, before and after γ-irradiation, showed that the unirradiated and irradiated PVA/PEG blends are more stable against thermal decomposition than pure PVA. Improvement in tensile mechanical properties of PVA/PEG blends was occurred.  相似文献   

12.
This paper investigated the influence of TiO2 nanoparticles on the morphologies, as well as crystallization behaviour and kinetics, of neat PLA and PCL, and of these polymers in different PLA/PCL blends. We used transmission electron microscopy to evaluate the morphologies of the systems, while the crystallization behaviour and kinetics were investigated through differential scanning calorimetry (DSC). In addition to standard and modulated (StepScan) DSC analyses, the self-nucleation temperatures of neat PCL and PCL in the different nanocomposites were determined, followed by a self-nucleation and annealing thermal fractionation analysis of PCL crystallization and an Avrami isothermal kinetic analysis of PCL crystallization and PLA cold crystallization. We found that the nanoparticles were well dispersed, but only in the PLA phase of the blends, with only a few on the interface or in the PCL phase. They did nucleate and accelerate, and influence the mechanism of, the PCL crystallization in neat PCL, but had little influence on PCL crystallization in the blends. They strongly influenced the rate of cold crystallization of PLA, but had little influence on this parameter in the blends. The tensile properties were also determined, and changes in these properties could be related to the morphologies of the systems.  相似文献   

13.
The presented work deals with blends composed of polyvinyl alcohol (PVA) and biopolymers (protein hydrolysate, starch, lignin). PVA does not belong to biologically inert plastics but its degradation rate (particularly under anaerobic conditions) is low. A potential solution to the issue problem lies in preparation of blends with readily degradable substrates. We studied degradation of blow-molded films made of commercial PVA and mentioned biopolymers in an aqueous anaerobic environment employing inoculation with digested activated sludge from the municipal wastewater treatment plant. Films prepared in the first experimental series were to be used for comparing biodegradation of blends modified with native or plasticized starch; in this case effect of plasticization was not proved. The degree of PVA degradation after modification with native or plasticized starch increases in a striking and practically same manner already at a starch level as low as approximately 5 wt.%. Films of the second experimental series were prepared as additionally modified with protein hydrolysate and lignin. Only lignin-modified samples exhibited a somewhat lower degree of biodegradation but regarding the measure of lignin present in blend this circumstance is not essential. Level of biodegradation with all discussed films differed only slightly—within range of experimental error.  相似文献   

14.
This study presents the effect of biodegradation, in a composting medium, on properties of membrane-like crosslinked and noncrosslinked polyvinyl alcohol (PVA) and nanocomposites. The composting was carried out for 120 days and the biodegradation of these materials was characterized using various techniques. The changes in the PVA resin and nanocomposite surface topography and microstructure during composting were also characterized. The results from the analyses suggest biodegradation of PVA based materials in compost medium was mainly by enzymes secreted by fungi. The results also indicate that the enzymes degraded the amorphous regions of the specimens first and that the PVA crystallinity played an important role in its biodegradation. The surface roughness of the specimens was seen to increase with composting time as the microbial colonies grew which in turn facilitated further microorganism growth. All specimens broke into small pieces between 90 and 120 days of composting as a result of deep biodegradation. Glyoxal and malonic acid crosslinking decreased the PVA biodegradation rate slightly. Addition of highly crystalline microfibrillated cellulose and naturally occurring halloysite nanotubes in PVA based nanocomposites also decreased the biodegradation rate. The three factors: PVA crystallinity, crosslinking and additives, may be utilized effectively to extend the life of these materials in real life applications.  相似文献   

15.
The objective of this study was to investigate the properties of poly(vinyl alcohol)/chitosan nanocomposite films reinforced with different concentration of amorphous LCNFs. The properties analyzed were morphological, physical, chemical, thermal, biological, and mechanical characteristics. Oil palm empty fruit bunch LCNFs obtained from multi-mechanical stages were more dominated by amorphous region than crystalline part. Varied film thickness, swelling degree, and transparency of PVA/chitosan nanocomposite films reinforced with amorphous part were produced. Aggregated LCNFs, which reinforced PVA/chitosan polymer blends, resulted in irregular, rough, and uneven external surfaces as well as protrusions. Based on XRD analysis, there were two or three imperative peaks that indicated the presence of crystalline states. The increase in LCNFs concentration above 0.5% to PVA/chitosan polymer blends led to the decrease in crystallinity index of the films. A noticeable alteration of FTIR spectra, which included wavenumber and intensity, was obviously observed along with the inclusion of amorphous LCNFs. That indicated that a good miscibility between amorphous LCNFs and PVA/chitosan polymer blend generated chemical interaction of those polymers during physical blending. Reinforcement of PVA/chitosan polymer blends with amorphous LCNFs influenced the changes of Tg (glass transition temperature), Tm (melting point temperature), and Tmax (maximum degradation temperature). Three thermal phases of PVA/chitosan/LCNFs nanocomposite films were also observed, including absorbed moisture evaporation, PVA and chitosan polymer backbone structural degradation and LCNFs pyrolysis, and by-products degradation of these polymers. The addition of LCNFs 0.5% had the highest tensile strength and the addition of LCNFs above 0.5% decreased the strength. The incorporation of OPEFB LCNFs did not show anti-microbial and anti-fungal properties of the films. The addition of amorphous LCNFs 0.5% into PVA/chitosan polymer blends resulted in regular and smooth external surfaces, enhanced tensile strength, increased crystallinity index, and enhanced thermal stability of the films.  相似文献   

16.
The rheologies, morphologies, crystallization behaviors, mechanical and thermal properties of poly(lactic acid) (PLA)/polypropylene (PP) blends and PLA/PP/maleic anhydride-grafted PP (MAPP) blends were investigated. The results showed that the complex viscosities of PLA/PP blends were between those of neat PLA and neat PP, and MAPP had a thinning effect on those of the blends. PLA/PP blends exhibited the distinct phase separation morphologies due to the limited partial miscibility of the blend components. MAPP slightly improved the miscibility between PLA and PP. Both the cold crystallization of PLA component and melt crystallization of PP component were enhanced, probably because PLA and PP were reciprocal nucleating agents. The tensile strength and flexural modulus decreased, while the tensile strain at break and heat deflection temperature (HDT) increased with the increasing PP content. MAPP had the positive effects on the notched impact strength and HDT of PLA-rich blends and also increased the flexural modulus of the binary blends. The thermal stability of the blend was improved by PP, and the incorporation of MAPP further enhanced the thermal stability.  相似文献   

17.
Poly(lactic acid) (PLA) presents high strength and modulus, but very low toughness as well as slow crystallization. Natural rubber (NR) was blended to enhance the toughness and nucleating agent was added to improve the crystallization. Cyclodextrin (CD), considered as a green compound, as well as calcium carbonate (CaCO3) and talc were used as nucleating agents. Effects of these nucleating agents on crystallization, mechanical properties and morphology of neat PLA and PLA/NR blend were investigated. It was found that the addition of talc and CD decreased cold crystallization temperature (Tcc) of the PLA. Same result was obtained in PLA/NR blend containing talc. All nucleating agents increased the degree of crystallinity (ΧC) of PLA, whereas only talc and CaCO3 increased ΧC of PLA in PLA/NR blends. The enhanced toughness of PLA by the addition of nucleating agent was attributed to its increased crystallinity, as well as decreased spherulite size. For PLA/NR blends, the increase in toughness was mainly contributed by the presence of the rubber.  相似文献   

18.
Multilayers of natural rubber (NR) and polyvinylalcohol (PVA) were processed by casting natural rubber latex (NRL) then PVA with varying layer thickness. Adhesion between NR and PVA was found to be very poor, as determined with the peel method. The films of interfacial blend were composed of NRL and PVA having different ratios as a layer between NR/PVA layer, possessing good adhesion and exhibited one mechanical phase in tensile-elongation at break tests. The result of adhesion was confirmed by thermogravimetric analysis and scanning electron microscopy study. Also, adhesion was too strong for delamination at the interface when the unit of three layers NR/blend/PVA was irradiated at 25 kGy. To probe the effect of the adhesion difference on mechanical behavior and deformation of NR/blend/PVA layers at dry and wet conditions, the peel strength was examined as a function of layer thickness and aging time. The results indicated that the interfacial blend, irradiation process and film thickness were the key parameters affecting adhesion of NR/PVA layer.  相似文献   

19.
采用臭氧氧化—A/O工艺处理聚乙烯醇(PVA)废水,研究了臭氧氧化时间、臭氧流量以及废水pH等因素对臭氧氧化效果的影响。实验结果表明:当气体臭氧质量浓度为30 mg/L、臭氧氧化时间为45 min、臭氧流量为4 L/min、废水pH为8时,PVA质量浓度从进水的93.2 mg/L降至4.5 mg/L;PVA溶液的BOD5/COD从0.014增加至0.310,可生化性明显改善;臭氧氧化—A/O工艺处理后出水COD降至50 mg/L左右,达到GB 8978—1996《污水综合排放标准》中的一级排放标准;出水PVA质量浓度为1.6 mg/L,明显优于A/O工艺(33.1 mg/L)。  相似文献   

20.
Biodegradable nanocomposites comprising of biodegradable polymers and bioactive organically modified layered silicates commonly reveal extremely enhanced mechanical and various other properties when compared to those of virgin polymers. This work was undertaken with a view to preparation of polymer bionanocomposites consisting of biodegradable poly(vinyl alcohol) (PVA) and organo-nanoclay. Cloisite Na+ and ammonium salt of l-isoleucine amino acid was used for the preparation of the novel chiral organo-nanoclay via an intercalation reaction in an aqueous solution. PVA/organo-nanoclay bionanocomposites of various compositions were created through the solution intercalation method by ultrasound-assisted technique. The resulting novel materials were characterized by X-ray diffraction and Fourier transform infrared spectroscopy techniques. Thermogravimetric analysis (TGA) and UV/vis spectroscopy were applied to test the properties of PVA bionanocomposites. TGA indicate that the thermal stability is enhanced distinctly, without a sacrifice in optical clarity. The improvement of thermal properties was attributed to the homogeneous and good dispersion of organo-nanoclay in polymeric matrix and the strong hydrogen bonding between O?CH groups of PVA and the oxygen atoms of silicate layers or carbonyl group as well as OH group of intercalated amino acid. The morphology of the organo-nanoclay and PVA bionanocomposites was examined by scanning electron microscopy and transmission electron microscopy techniques. Uniform distribution of clay due to intimate interaction between clay and polymer appears to be the cause for improved properties.  相似文献   

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