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1.
New types of composites were prepared using low-density polyethylene (LDPE) filled with modified organic filler, Canadian switch grass coated with polypyrrole (PPy). The grass surface was entirely covered when 10 wt.% of pyrrole was used for the modification, as confirmed by scanning electron microscopy and infrared spectroscopy. LDPE composites filled with modified grass were prepared by melt mixing and their properties were compared with the properties of the composites filled with unmodified grass. The influence of crosslinking, induced by 1 wt.% of peroxide, on mechanical, thermal and electrical properties of the composites was investigated. Crosslinking enhanced the tensile strength of the prepared composites in the entire range of the filler content. The Young’s modulus of the composites prepared by crosslinking is slightly lowered when compared with the uncrosslinked composites if the filler content is less than 60 wt.%, for higher filler content it is increased. The conductivity of the uncrosslinked composites containing 40 wt.% of grass modified by PPy was in the range 1 × 10−6 S cm−1, which is a value by 5 orders of magnitude higher than the conductivity of the crosslinked materials. The presence of PPy on grass surface leads to a reduction of crosslinking of the LDPE matrix.  相似文献   

2.
The properties and biodegradation behavior of blends of poly(lactic acid) (PLA) and ethylene-vinyl acetate-glycidylmethacrylate copolymer (EVA-GMA), and their composites with cellulose microfibers (CF) were investigated. The blends and composites were obtained by melt mixing and the morphology, phase behavior, thermal and rheological properties of PLA/EVA-GMA blends and PLA/EVA-GMA/CF composite films were investigated as a function of the composition. The disintegrability in composting conditions was examined by means of morphological, thermal and chemical analyses to gain insights into the post-use degradation processes. The results indicated a good compatibility of the two polymers in the blends with copolymer content up to 30 wt.%, while at higher EVA-GMA content a phase separation was observed. In the composites, the presence of EVA-GMA contributes to improve the interfacial adhesion between cellulose fibers and PLA, due to interactions of the epoxy groups of GMA with hydroxyls of CF. The addition of cellulose microfibers in PLA/EVA-GMA system modifies the rheological behavior, since complex viscosity increased in presence of fibers and decreased with an increase in frequency. Disintegration tests showed that the addition of EVA-GMA influence the PLA disintegration process, and after 21 days in composting conditions, blends and composites showed faster degradation rate in comparison with neat PLA due to the different morphologies induced by the presence of EVA-GMA and CF phases able to allow a faster water diffusion and an efficient PLA degradation process.  相似文献   

3.
The methods for producing reference test materials for biodegradation evaluation tests have been studied. Mechanical crushing at low temperature of polymer pellets using dry ice was selected for the method of producing polymer powder of poly(lactic acid) (PLA). The powders were fractionated using 60 mesh (250 μm) and 120 mesh (125 μm) sieves. The size distributions were then measured. The average diameter of the PLA particles obtained by this method was 214.2 μm. The biodegradation speeds of these PLA polymer powders were evaluated by two methods based on the international standard and one in vitro method based on the enzymatic degradation. First, the degree of biodegradation for this PLA powder was 91% for 35 days in a controlled compost determined by a method based on ISO 14855-1 (JIS K6953) at 58 °C managed by the Mitsui Chemical Analysis and Consulting Service, Inc. (Japan). Second, these polymer powders were measured for biodegradation by the Microbial Oxidative Degradation Analyzer (MODA) in a controlled compost at 58 °C and 70 °C based on ISO/DIS 14855-2 under many conditions. The degree of biodegradation for this PLA powder was approximately 80% for 50 days. In addition, the polymer powders were biodegraded by Proteinase K which is a PLA degradation enzyme. This polymer powder was suitable as a reference material for the evaluation methods of biodegradation.  相似文献   

4.
Degradation of short sisal fibres/Mater Bi-Y™ biocomposites during indoor burial experiments was analysed. Within the first month, water sorption was the main event followed by weight loss. Water sorption results demonstrated that composites absorbed less water than the matrix. The lower sorption capacity of composites was related to the presence of fibre-fibre and fibre-matrix (both of carbohydrate nature) interactions which delay the water intake and enhances the material stability. In soil burial, all materials followed the same degradation pattern. The amorphous nature of the matrix favoured the preferential removal of starch, which was the most bio-susceptible material, as observed by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Fibres seemed to play a secondary role in this process, as confirmed by the slight difference in weight loss between the matrix and composites (40 and 33 wt.%, respectively). The drop in mechanical properties as a function of the exposure time was associated with the preferential loss of matrix and fibre components and the detriment of the fibre/matrix interface.  相似文献   

5.
Composites of poly(methyl methacrylate) (PMMA) with multi-walled carbon nanotubes (MWCNT) of varying aspect ratio and carboxylic acid functionality were prepared using melt mixing. The extent of dispersion and distribution of the MWCNTs in the PMMA matrix was investigated using a combination of high-resolution transmission electron microscopy (HRTEM), wide-angle X-ray diffraction (XRD) and Raman spectroscopy. The electrical resistivity and oscillatory shear rheological properties of the composites were measured as a function of MWCNT geometry, functionality, and concentration. The fundamental ballistic conductance of the pristine free-standing MWCNTs was investigated using a mechanically controlled break-junction method. The electrical conductivity of PMMA was enhanced by up to 11 orders of magnitude for MWCNT concentrations below 0.5 wt.%. MWCNTs having higher aspect ratio, above 500, or functionalized with carboxylic acid groups readily formed rheological percolated networks with thresholds, determined from a power law relationship, of 1.52 and 2.06 wt.%, respectively. The onset of pseudo-solid-like behaviour and network formation is observed as G′, η∗, and tan δ−1 are independent of frequency as MWCNT loading increased. Sufficiently long and/or functionalized tubes are required to physically bridge or provide interfacial interactions with PMMA to alter polymer chain dynamics. Carboxylic acid functionalization disrupts the crystalline order of MWCNTs due to a loss of π-conjugation and electron de-localisation of sp2 C-C bonds resulting in non-ballistic electron transport in these tubes, irrespective of how highly dispersed they are in the PMMA matrix.  相似文献   

6.
The biodegradabilities of poly(?-caprolactone) (PCL) powders (av. size = 180.7 μm) in controlled compost at 58 °C have been studied using the microbial oxidative degradation analyzer (MODA) based on ISO 14855-2 entitled “Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions - Method by analysis of evolved carbon dioxide - Part 2: Gravimetric measurement of carbon dioxide evolved in a laboratory-scale test”. The biodegradability of the PCL powders was 101.4% in a 56-day test period by the ISO method. The biodegradabilities of PCL powders have been studied using percent modern carbon (pMC) measured by accelerated mass spectrometry (AMS). Trapped CO2 was analyzed by AMS to determine the pMC (sample) using 14C radiocarbon concentration. By using the theory that the pMC (sample) was the sum of pMC (compost) (104.88%) and pMC (PCL) (0%) as the respective ratios in the determined period, CO2 (respiration) was calculated only from one reaction vessel. The biodegradability of PCL powders was 79.9% in a 56-day test period by the AMS method. It was found that respiration activities in the sample vessel including PCL, compost and sea sand were the same as that in the blank vessel including compost and sea sand without PCL during the active biodegradation period (0-33 day) at 58 °C. It was confirmed that respiration activities in the sample vessel were slightly higher than that in the blank vessel after active biodegradation due to the propagation of microorganisms using energy and metabolites by PCL biodegradation during those periods.  相似文献   

7.
It is well known that the ferroelectric performance of poly (vinylidene fluoride) (PVDF) is caused by its β-crystal structure, which can be efficiently induced through a stretching process applied to the PVDF. Though numerous PVDF nanocomposites have been reported on, there is still a lack of studies on how the stretching process affects the phase transformation in PVDF nanocomposites. In this study, the effects of stretching on the crystalline structures and alternating current (AC) conductivity of PVDF nanocomposites with different concentrations (up to 5.0 wt.%) of CNFs were investigated. Results revealed that the stretching process is not only an effective approach to produce β-crystal from pure PVDF, but also for CNF/PVDF composites. The extremely high phase transformation from α- to β-crystal (?96%) is maintained for the nanocomposites with above 1.0 wt.% CNFs. The AC conductivity of CNF/PVDF composites remarkably decreases when the resultant percolation threshold is raised from 1.0 to 4.2 wt.% CNFs after stretching. This is attributed to the reduced crystallinity induced by the phase transformation from α- to β-PVDF as well as the CNF re-orientation.  相似文献   

8.
A novel flame retardant system of poly(vinyl alcohol) (PVA) is prepared via using ammonium polyphosphate (APP) and layered double hydroxide (LDH). The flammability of PVA composites containing APP-based LDH at a 15 wt.% global percentage showed that the flame retardancy of all PVA/APP/LDH samples increase with the increase of LDH concentration in the range of 0.1-1.0 wt.%, and reach a LOI value of up to 33 and UL-94 V-0 rating for most composites. Thermo-gravimetric analysis reveals that PVA/APP/LDH samples show higher initial decomposition temperature in comparison with PVA/APP composite. The morphology and structures of residues generated during LOI test were investigated by scanning electronic microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the composition of the residue formed after thermo-oxidation to support a fundamental analysis for the mechanism of char formation. The test of mechanical properties demonstrated that LDH can enhance tensile strength, Young's modulus and elongation at break of PVA/APP composites.  相似文献   

9.
Microextraction by packed sorbent (MEPS) is a new technique for sample preparation that can be connected on-line with LC or GC. In MEPS, approximately 1-2 mg of the solid packing material is inserted into a syringe (100-250 μL) as a plug. Sample preparation takes place on the packed bed. The bed can be packed or coated to provide selective and suitable sampling conditions. The new method is very promising for extraction of drugs and metabolites from biological samples.In this paper, some factors affecting the performance of MEPS such as recovery, carry-over, leakage, washing volume and elution volume were studied using C18 and hydroxylated polystyrene-divinylbenzene copolymer (ENV+) as sorbents. Radioactively labelled bupivacaine in plasma samples was used as test analyte. For the extraction of this drug, using methanol/water 95:5 (v/v) (0.25% ammonium hydroxide) was used as elution solvent. The analyte response increased with increasing the elution volume and it was linear upp up to 100 μL utilizing liquid scintillation counter. Further, for concentrating the sample, we found that MEPS may be used such that the sample can be drawn through the needle, up and down, several times. The analyte leakage increases as the volume washing increases, though higher washing volumes may also result in cleaner extracts. To eliminate analyte carry-over, the sorbents were washed first with 3 × 250 μL elution solution and then with 3 × 250 μL washing solution. In addition, the reproducibility measurements show relatively good relative standard deviation (RSD) % values concerning analyte recovery and analyte leakage. The present study provides an understanding of basic aspects when optimizing methods for MEPS. In this study, MEPS was used off-line with liquid scintillation counter and on-line with LC-MS/MS.  相似文献   

10.
Poly(phenylene sulfide)/ferrosoferric oxide composites (PPS/Fe3O4) with various loading levels were prepared by melt compounding. The microstructure of composites was investigated using SEM and XRD. The rheological, electrical and magnetic properties were characterized respectively by the parallel plate rheometer, high resistance meter, and magnetometer. The results reveal that the Fe3O4 particles are well dispersed in the PPS matrix due to their nice affinity, which results in a weak strain overshoot at large amplitude oscillatory level. Both the rheological and the electrical responses of the composites show a typical percolation behavior. But the rheological percolation presents lower threshold (< 40 wt %) than that of electrical percolation (~ 50 wt %), which is attributed to the difference structure of the percolation network. The magnetic response, however, shows good linear relation with Fe3O4 loadings, indicating that the physical percolation has little influence on the magnetic properties. This is mainly due to the yielded long‐range magnetic interactions among Fe3O4 particles in the applied field, which are far stronger than those nonmagnetic physical interactions accounting for percolation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 233–243, 2008  相似文献   

11.
The effect of the C/O ratio of graphene oxide materials on the reinforcement and rheological percolation of epoxy-based nanocomposites has been studied. As-prepared graphene oxide (GO) and thermally-reduced graphene oxide (TRGO) with higher C/O ratios were incorporated into an epoxy resin matrix at loadings from 0.5 to 5 wt %. Tensile testing revealed good reinforcement of the polymer up to optimal loadings of 1 wt %, whereas agglomeration of the flakes at higher loadings caused the mechanical properties of the composites to deteriorate. The level of reduction (C/O) of the graphene oxide filler was found to influence the mechanical and rheological properties of the epoxy composites. Higher oxygen contents were found to lead to stronger interfaces between graphene and epoxy, giving rise to higher effective Young's moduli of the filler and thus to superior mechanical properties of the composite. The effective modulus of the GO in the nanocomposites was found to be up to 170 GPa. Furthermore, rheological analysis showed that highly oxidized graphene flakes did not raise the viscosity of the epoxy resin significantly, facilitating the processing considerably, of great importance for the development of these functional polymeric materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 281–291  相似文献   

12.
As the cellulose acetate butyrate possessed multichiral carbon atoms in its molecular structure unit, enantioselective membrane was prepared using cellulose acetate butyrate as membrane material. The flux and permselective properties of membrane using aqueous solutions of (R,S)-2-phenyl-1-propanol as feed solution was studied. The top surface and cross-section morphology of the resulting membranes were examined by scanning electron microscopy. When the membrane was prepared with 15 wt.% cellulose acetate butyrate and 20 wt.% DMF in the casting solution, and the operating pressure and feed concentration of racemate were 2 kgf/cm2 and 5 mmol/L, respectively, over 98% of enantiomeric excess (e.e.) was obtained. This is a report, for the first time, that the cellulose acetate butyrate is used as optical resolution membrane material for isolating the optical isomers of (R,S)-2-phenyl-1-propanol.  相似文献   

13.
Crosslinked materials derived from poly(lactide) (PLA) have been produced by radiation modification in the presence of a suitable crosslinker (triallyl isocyanurate) (TAIC). The crosslinking structure introduced in PLA films has not only much improved the heat stability but also their mechanical properties. The properties of crosslinked samples are governed by crosslinking density and these improvement seemed to increase with radiation dose. This implied that the three dimensional networks have been introduced in material by radiation and the crosslinking density depended on the structure and length of PLA chains. Biodegradability of PLA was also determined by an enzymatic degradation test and burying in compost at 55 °C. Differing with PLLA, PDLA was insignificantly degraded by proteinase K. The degradation rate of PLA in compost was postponed with the introduction of crosslinks.  相似文献   

14.
The suitability of the use of macroporous adsorbent Amberlite XAD7HP in expanded bed adsorption processes for the isolation of flavonoids from crude extracts of Ginkgo biloba L. has been assessed. The expansion and hydrodynamic properties of expanded beds were investigated and analyzed. The bed expansion as a function of operational fluid velocity was measured and correlated with the Richardson–Zaki equation. Theoretical predictions of the correlation parameters (the terminal settling velocity ut and exponent n) were improved by modifying equations in the literature. Residence time distributions (RTDs) were studied using acetone as a tracer. Three measures of liquid phase dispersion (the height equivalent of theoretical plate, Bodenstein number and axial distribution coefficient) were investigated and compared to values previously obtained with commercial EBA adsorbents developed for protein purification. A suitable bed expansion ratio was found to be 1.25 times the settled bed height, which occurred at a corresponding flow velocity of 183 cm/h. For an initial settled bed height of 42 cm, the mean residence time of liquid in the expanded bed was around 28 min. Under these flow conditions, the axial mixing coefficient Dax was 7.54 × 10−6 m2/s and the Bodenstein number was 28; the number of theoretical plates (N) was 19 and the height equivalent of a theoretical plate (HETP) was 2.77 cm. Rutin trihydrate was used as a model flavonoid for the characterization of the adsorption properties of Amberlite XAD7HP. Adsorption was observed to reach equilibrium within 3 h with 70% of the adsorption capacity being achieved within 30 min. The estimated maximum equilibrium adsorption capacity for rutin was estimated to be 43.0 mg/(g resin) when the results were fitted to Langmuir isotherms. The adsorption performance was not seriously impaired by the physical presence of G. biloba leaf powders. Assessment of the kinetics of the adsorption of rutin revealed that the rate constant for adsorption was only reduced by 15% in the presence of leaf powders at a concentration of 50 mg/mL. The results demonstrated that Amberlite XAD7HP should be suitable for expanded bed adsorption of flavonoids from crude extracts of G. biloba L.  相似文献   

15.
Granular cornstarch was treated with microbial glucoamylase (50 mM sodium acetate buffer at pH 5.5 at 30 °C, 150 rpm) for up to 8 h. Treated starch was recovered and evaluated for changes in granular morphology, chemical properties, thermal properties, crystallinity and impact on its biodegradability. As the enzyme treatment progressed, reducing sugars began to accumulate in the liquid culture media (total of 6% in 8 h) and the granule suffered roughly 6% weight loss within 8 h of incubation. While the granules appeared intact morphologically, numerous small pits developed throughout the surface of the granules as a result of the enzyme treatment. Even after 8 h of enzyme treatment, the pitted granules were not disrupted and remained intact. X-ray diffraction indicated no loss of crystallinity in the enzyme treated granules but rather an increase in relative crystallinity, suggesting that the enzyme preferentially catalyzed the anhydroglucose units in amorphous regions of the granule. These findings were further supported by FTIR data suggesting that granules become more resistant to enzyme attack as amorphous amylose is hydrolyzed faster than the crystalline amylopectin domains. These results also suggest that variations in the crystallinity of different types of starches have the potential to affect their rates of biodegradation. Enzyme treated starch granules exhibited resistance to biodegradation, and the degree of resistance was related to the length of enzyme treatment. Granules treated with enzyme for a total of 7 h and subjected to biodegradation in soil produced 40-50% less CO2 in a closed circuit respirometer compared to the untreated samples. Differential scanning calorimetry (DSC) thermograms showed an endothermic reaction with little change in the onset and peak temperatures indicating that glucoamylase started by degrading the starch granules from the surface.  相似文献   

16.
Poly(vinyl alcohol) (PVA) is considered to be one of the very few vinyl polymers soluble in water and susceptible to biodegradation in aqueous media by specific microorganisms, implying oxidation of the carbon backbone followed by a random endocleavage of the polymer chains. The overall process does not appear to be appreciably affected by either degree of polymerization (DPn) or degree of hydrolysis (HD) of PVA at least in the 100-1000 and 80-100% ranges, respectively.In order to assess the effect of HD on the biodegradation propensity of PVA, different PVA samples having similar DPn and noticeably different HD values were synthesized by controlled acetylation of commercial PVA (HD = 99%) and submitted to biodegradation tests in aqueous medium, mature compost and soil by using respirometric procedures. Re-acetylated PVA samples characterized by HD of between 25 and 75% underwent extensive mineralization when buried in solid media, whilst PVA (HD = 99%) showed recalcitrance to biodegradation under those conditions. An opposite trend was indeed observed in aqueous solution, thus suggesting that biodegradation is not an absolute attribute directly related to structural features of the substrate under investigation. Boundary conditions related to the framework under which the biodegradation assessment is undertaken have to be taken into account and specifically well defined.  相似文献   

17.
LDPE and its blend with cellulose, obtained by extrusion, were UV-irradiated with different doses or biodegraded in soil up to 1 year. Simultaneously, the same samples were 1 year biodegraded after 20 h UV pre-irradiation in the same conditions. The course of photo- and biodegradation was monitored by estimation of average molecular weights and polydispersity, gel amount, changes of PE crystallinity and mechanical properties. Moreover, the biodegradation degree was calculated on the basis of carbon dioxide evolved and surface morphological changes were observed by SEM. It was found that biodegradation of PE + cellulose is hampered by intermolecular crosslinking of both components. Although, the rate of decomposition of PE + cellulose blends is low it is enough for disintegration of such materials in the natural environment.  相似文献   

18.
Carbon black coated with polyaniline, forming a core-shell structure, was synthesized by in situ polymerization at different carbon black contents (5-30 wt.%) and introduced into epoxy resin to be a microwave absorber. The spectroscopic characterizations of the formation processes of polyaniline/carbon black composites were studied using Fourier transform infrared, ultraviolet-visible spectrophotometer, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron spin resonance. Microwave absorbing properties were investigated by measuring reflection loss in the 2-18 and 18-40 GHz microwave frequencies range using the free space method. The results showed that a wider absorption frequency range could be obtained by adding different carbon black contents in polyaniline.  相似文献   

19.
The objective of this study was to develop a novel kind of hyaluronic acid-based biomaterials which had the great potentials to be used as dermal fillers or applied in tissue augmentation or filling. A series of sponge-like composites were prepared by cross-linking different amounts of hyaluronic acid (HA) and carboxymethylcellulose sodium (CMC-Na). Adipic dihydrazide (ADH) was employed as the cross-linker and water-soluble 1-ethyl-3-[3-(dimethylaminopropyl)] carbodiimide (EDC) as the carboxyl-activating agent. Fourier-Transform Infrared (FT-IR) analysis was performed to characterize the expected amide linkages in the cross-linked composites, and the scanning electron microscopic (SEM) analysis was carried out to view the microstructures of the composites. Furthermore, the physico-chemical properties, such as swelling property, thermostability, the resistance to hyaluronidase (HAse) degradation and the antioxidant abilities against hydroxyl free radical (OH), were characterized. The presence of the amide peak at 1476.11 cm−1 in FT-IR spectra indicated the cross-linking between HA and CMC-Na by ADH. As demonstrated by scanning electron microscopy (SEM), the microstructures of the composites were dependent on HA content. The equilibrium swelling ratio was 20.091 ± 0.070, indicating the excellent water-uptake abilities of the composites. The HA-CMCNa composites showed a thermal stability up to 237 °C, independent of the composition of the prepared biomaterials. When exposed to phosphate-buffered saline (PBS) solution containing HAse (100 U/ml), all of the composites could be degraded quickly in 15 h. But when the concentrations of ADH and EDC in the cross-linking reaction system were increased up to 10 mmol/L, respectively, the degradation process lasted for 60 h. The prepared composites possessed great antioxidant abilities against OH and the ability to scavenge OH depended on the composition. With the high water-keeping ability and improved physico-chemical stabilities, the prepared biocompatible HA-CMCNa composites could be used as ideal alternatives for dermal fillers, tissue augmentation/filling biomaterials.  相似文献   

20.
This paper presents a fully automated method for determining ten primary amines in wastewater at ng/L levels. The method is based on simultaneous derivatization with pentafluorobenzaldehyde (PFBAY) and headspace solid-phase microextraction (HS-SPME) followed by gas chromatography coupled to ion trap tandem mass spectrometry (GC–IT-MS–MS). The influence of main factors on the efficiency of derivatization and of HS-SPME is described in detail and optimized by a central composite design. For all species, the highest enrichment factors were achieved using a 85 μm polyacrylate (PA) fiber exposed in the headspace of stirred water samples (750 rpm) at pH 12, containing 360 g/L of NaCl, at 40 °C for 15 min. Under optimized conditions, the proposed method achieved detection limits ranging from 10 to 100 ng/L (except for cyclohexylamine). The optimized method was then used to determine the presence of primary amines in various types of wastewater samples, such as influent and effluent wastewater from municipal and industrial wastewater treatment plants (WWTPs) and a potable water treatment plant. Although the analysis of these samples revealed the presence of up to 1500 μg/L of certain primary amines in influent industrial wastewater, the concentration of these compounds in the effluent and in municipal and potable water was substantially lower, at low μg/L levels. The new derivatization–HS-SPME–GC–IT-MS–MS method is suitable for the fast, reliable and inexpensive determination of primary amines in wastewater in an automated procedure.  相似文献   

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