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 15 毫秒
1.
In the present study, the effects of intumescent flame retardant (IFR) incorporating organically modified montmorillonite (O‐MMT) on the flame retardancy and melt stability of PLA were investigated. The flame‐retardant PLA was prepared using a twin‐screw extruder and a two roll mill. Then, the influence of IFR and MMT on flame retardancy and melt stability was thoroughly investigated by means of limiting oxygen index (LOI), vertical burning test, thermogravimetric analysis, scanning electronic microscopy, melt flow index (MFI), and parallel plate rheological experiments. The experimental results show that the IFR system in combination with MMT has excellent fire retardancy, i.e. the sample could achieve a UL94 V‐0 rating and LOI value increases from 20.1 for pristine PLA to 27.5 for the flame‐retarded PLA. MFI and rheological measurement indicate that O‐MMT significantly enhances the melt stability and suppresses the melt dripping. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

2.
Because of good thermal stability, nonflammability and rich structural designability, ionic liquids (ILs) have been used as flame retardants for poly(lactic acid) (PLA). However, as a small molecule, IL has the disadvantages of poor thermal stability and water resistance, and so on. In this paper, an imidazole‐type poly(ionic liquid) (PIL) containing a phosphate anion was synthesized using 1‐vinylimidazole, triethyl phosphate, and 1,2‐divinylbenzene and marked as PDVE[DEP]. The PDVE[DEP] was used to improve the flame retardancy of PLA. The flame retardancy and thermal degradation behaviors of PLA/PDVE[DEP] composites were investigated by the limited oxygen index (LOI), UL‐94 vertical burning, cone calorimetry, and thermal gravity analysis, and so on. The results showed that only 1.0 wt% PDVE[DEP] allows PLA to achieve the UL‐94 V0 rating and obtain LOI value 25.6 vol%. The PDVE[DEP] improve the flame retardancy of PLA by melting‐away mode. In addition, it catalyzes the transesterification of PLA and changes the degradation products.  相似文献   

3.
A crosslinked silicone‐containing macromolecular charring agent (CSi‐MCA) was synthesized via “one‐pot” process, and it was combined with ammonium polyphosphate (APP) to synergistically improve the flame retardancy of poly(l ‐lactic acid) (PLA). The chemical structure of synthesized CSi‐MCA was characterized by Fourier transform infrared spectroscopy and solid‐state 13C nuclear magnetic resonance. The thermal gravimetric analyzer indicated that the CSi‐MCA displayed good thermal stability and high residue via the catalytic crosslinking. Furthermore, the flame retardant effect of CSi‐MCA and APP as intumescent flame retardants in PLA system was investigated by limited oxygen index, UL94, and cone calorimeter test. When the content of CSi‐MCA was 5 wt% and APP was 10 wt% (CSi‐MCA/APP = 1/2), the limited oxygen index value of composites was 33.6 and UL94 classed a V‐0 rating. The peak heat release rate and total heat release of PLA composites containing both APP and CSi‐MCA decreased significantly in comparison with those with APP or CSi‐MCA alone. The flame retardancy mechanism was investigated via analyzing residual chars by scanning electron microscopy and X‐ray photoelectron spectroscopy as well as the possible chemical reaction between APP and CSi‐MCA by thermal gravimetric analyzer and Fourier transform infrared spectroscopy. The results showed that the enhanced flame retardancy was attributed mainly to synergistic effect of CSi‐MCA and APP, which could form a compact, continuous, and protective layer during combustion. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

4.
Two types of three‐arm and four‐arm, star‐shaped poly(D,L ‐lactic acid‐alt‐glycolic acid)‐b‐poly(L ‐lactic acid) (D,L ‐PLGA50‐b‐PLLA) were successfully synthesized via the sequential ring‐opening polymerization of D,L ‐3‐methylglycolide (MG) and L ‐lactide (L ‐LA) with a multifunctional initiator, such as trimethylolpropane and pentaerythritol, and stannous octoate (SnOct2) as a catalyst. Star‐shaped, hydroxy‐terminated poly(D,L ‐lactic acid‐alt‐glycolic acid) (D,L ‐PLGA50) obtained from the polymerization of MG was used as a macroinitiator to initiate the block polymerization of L ‐LA with the SnOct2 catalyst in bulk at 130 °C. For the polymerization of L ‐LA with the three‐arm, star‐shaped D,L ‐PLGA50 macroinitiator (number‐average molecular weight = 6800) and the SnOct2 catalyst, the molecular weight of the resulting D,L ‐PLGA50‐b‐PLLA polymer linearly increased from 12,600 to 27,400 with the increasing molar ratio (1:1 to 3:1) of L ‐LA to MG, and the molecular weight distribution was rather narrow (weight‐average molecular weight/number‐average molecular weight = 1.09–1.15). The 1H NMR spectrum of the D,L ‐PLGA50‐b‐PLLA block copolymer showed that the molecular weight and unit composition of the block copolymer were controlled by the molar ratio of L ‐LA to the macroinitiator. The 13C NMR spectrum of the block copolymer clearly showed its diblock structures, that is, D,L ‐PLGA50 as the first block and poly(L ‐lactic acid) as the second block. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 409–415, 2002  相似文献   

5.
The economic and environmentally friendly flame‐retardant compound, tetramethyl (6‐chloro‐1,3,5‐triazine‐2,4‐diyl)bis(oxy)bis(methylene) diphosphonate ( CN‐1 ), was synthesized by a simple two‐step procedure from dimethyl phosphate, and its chemical structure was characterized by 1H, 13C, and 31P nuclear magnetic resonance and gas chromatography mass spectroscopy. Using the traditional pad–dry–cure method, we obtained several different add‐ons (wt%) by treating cotton twill fabric with flame retardant ( CN‐1 ). Thermogravimetric analysis, in an air and nitrogen atmosphere, of the modified cotton showed that decomposition occurred ~230°C with 16% residue weight char yield at 600°C, indicating high thermal stability for all treated levels. Limiting oxygen index (LOI) and the vertical flammability test were employed to determine the effectiveness of the flame‐retardant treatments on the fabrics. LOI values increased from ~18 vol% oxygen in nitrogen for untreated fabric to maximum of 34 vol% for the highest treatment level. Fabrics with higher levels of flame retardant also easily passed the vertical flammability test. Furthermore, Fourier transform infrared and scanning electron microscopy were utilized to characterize the chemical structure as well as the surface morphology of the flame‐retardant treated twill fabrics, including char area and the edge between unburned fabric and char area. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

6.
《先进技术聚合物》2018,29(4):1294-1302
For the sake of improving the flame retardancy of epoxy resin (EP), a novel phosphorus‐containing phenolic resin (PPR) synthesized in our group instead of conventional phenolic resin (PR) was used to cure EP in the present research. The curing processes and the corresponding crosslinking structure and mechanical performance were investigated by differential scanning calorimeter and dynamic mechanical thermal analysis. Because of the introduction of flame‐retarding elements including P and Si, PPR exhibited higher charring capacity in the condensed phase, which is helpful to construct a char layer of higher quality. Correspondingly, PPR‐cured EP displayed remarkably improved flame retardance as compared to conventional PR‐cured EP through the related evaluations including limiting oxygen index, vertical burning test, and microscale combustion colorimeter. As a multifunction agent, it is believable that PPR possesses potential commercial value to prepare flame‐retardant EP with high performance.  相似文献   

7.
In this study, a novel drug‐carrying micelle composed of methoxy poly(ethylene glycol) (mPEG)‐b‐poly(L‐lactic acid) (PLLA) with gas‐forming carbonate linkage was fabricated. Here, the gas‐forming carbonate linkage was formed by the chemical coupling of the terminal hydroxyl group of the PLLA block and benzyl chloroformate (BC). mPEG‐b‐PLLA‐BC was self‐organized in aqueous solution: the PEG block on the hydrophilic outer shell and the PLLA‐BC block in the hydrophoboic innor core. The cleavage of carbonate linkage by hydrolysis and formation of carbon dioxide nanobubbles in the micellar core enabled an accelerated release of the encapsulated anticancer drug (doxorubicin: DOX) from the mPEG‐b‐PLLA‐BC micelles. The amount of drug (DOX) released from the mPEG‐b‐PLLA‐BC micelle was higher than that from the conventional mPEG‐b‐PLLA micelle, which allowed for increased in vitro toxicity against KB tumor cells. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

8.
Novel halogen‐free compounds [9,10‐dihydro‐9‐oxa‐10‐phosphaphanthrene‐10‐oxide/vinyl methyl dimethoxysilane/N‐β‐(aminoethyl)‐γ‐aminopropyl methyl dimethoxysilane (DOPO–VMDMS–NMDMS)] that simultaneously contain phosphorus, nitrogen, and silicon have been synthesized through the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphanthrene‐10‐oxide (DOPO), vinyl methyl dimethoxysilane (VMDMS), and N‐β‐(aminoethyl)‐γ‐aminopropyl methyl dimethoxysilane (NMDMS). The chemical structure and properties of DOPO–VMDMS–NMDMS have been investigated with Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, phosphorous nuclear magnetic resonance, and thermogravimetric analysis (TGA). These synthesized flame retardants have been blended with a poly[2,2‐propane‐(bisphenol) carbonate]/acrylonitrile butadiene styrene (PC/ABS) alloy. The flame‐retardant properties of these mixture samples have been estimated with the limiting oxygen index (LOI), and the thermal stability has been characterized with TGA. The LOI value of PC/ABS/DOPO–VMDMS–NMDMS is enhanced up to 27.2 vol % from 21.2 vol %, and the char yield is also improved slightly (from 12 to 17%) with 2.8 wt % phosphorus, 3.0 wt % silicon, and 0.5 wt % nitrogen (at a 30 wt % loading of DOPO–VMDMS–NMDMS). The results show that there is a synergistic effect of the elements phosphorus, silicon, and nitrogen on the flame retardance. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1542–1551, 2007  相似文献   

9.
A highly cross‐linked poly (cyclotriphosphazene‐resveratrol) microsphere (PRV) was synthesized by using hexachlorocyclotriphosphazene (HCCP) and bio‐based resveratrol (REV) as raw materials, and the obtained PRV microspheres were applied to improve the flame retardancy and mechanical property of epoxy resin (EP). The TGA results showed that the PRV microsphere is an excellent charring agent and the char yield is as high as 62% at 800°C. The incorporation of PRV makes the initial degradation earlier yet significantly increases the char residue of EP composites. Moreover, the introduction of PRV microspheres into EP greatly promoted the flame retardancy performance. Under 3% of addition of PRV microspheres, the peak heat release rate (PHRR) and total heat release (THR) were decreased by 58.3% and 29.6%, respectively, the limited oxygen index (LOI) value was increased to 29.7% from 25.3% of pure EP. In addition, because of the uniform distribution in EP matrix and the enhancing effect of PRV microspheres, the mechanical properties including tensile modulus of EP composites were strengthened. PRV microspheres in this paper provide a possibility to synthesize a dual functional filler, which acts as both flame retardant and strengthening agent.  相似文献   

10.
In this communication, we reported the sequence variation of stereocomplex crystals (SC) and homocrystals (HC) in poly(l ‐lactic acid)/poly(d ‐lactic acid) (PLLA/PDLA) racemic blends melts. It was evidenced that the emerging sequence of the SC and HC depends on the hydrogen bond formation in the melt, and the hydrogen bond is required for the stereocomplexation in PLLA/PDLA racemic blend. First, by combining a commercial fast‐scan chip‐calorimeter (Flash DSC 1) and micro‐FTIR, we found that hydrogen bonds were formed in the melt during cooling at 2.5 K/s, but not at 3000 K/s. Second, annealing the melt without hydrogen bonds at 100 °C led to HC emerging first, while annealing the melt with hydrogen bonds resulted in SC emerging at first. Third, the crystallization kinetics of the racemic blends after cooling to predefined Tc at 2.5 or 3000 K/s further verified that the hydrogen bonding can be inhibited effectively by cooling the racemic blends isotropic melt at fast enough rate. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 83–88  相似文献   

11.
A multiblock copoly(ester–ether) consisting of poly(l ‐lactic acid) (PLLA) and poly(oxypropylene‐co‐oxyethylene) (PN) was prepared and characterized. Preparation was done via the solution polycondensation of a thermal oligocondensate of l ‐lactic acid, a commercially available telechelic polyether (PN: Pluronic‐F68), and dodecanedioic acid as a carboxyl/hydroxyl adjusting agent. When stannous oxide was used as the catalyst, the molecular weight of the resultant PLLA/PN block copolymers became very high (even with a high PN content) under optimized reaction conditions. The refluxing of diphenyl ether (solvent) at reduced pressure allowed the efficient removal of the condensed water from the reaction system and the feed‐back of the intermediately formed l ‐lactide at the same time in order to successfully bring about a high degree of condensation. The copolymer films obtained by solution casting became more flexible with the increasing PN content as soft segments. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1513–1521, 1999  相似文献   

12.
An aryl polyphenylphosphonate, poly(9-oxa-10-(2,5-dihydro-xyphenyl) phospha-phenanthrene-10-oxide) phenylphosphonate (WLA-3), was used to prepare a flame-retardant poly(lactic acid) (PLA) by direct melt compounding. The thermal behaviour, burning behaviour and mechanical properties of the flame-retardant PLA systems have been investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), vertical burning test (UL-94), limiting oxygen index (LOI), cone calorimeter test (CCT) and tensile test. The flame retardance mechanism has been studied via Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and P content analysis. The UL-94 ratings of PLA’s containing 7phr (W7P) and 10phr (W10P) of WLA-3 were enhanced to V-0 from no rating for neat PLA. However, the cone calorimetry of flame-retardant PLA (W7P) only showed a little decrease in heat release rate (HRR), peak of heat release rate (PHRR) and total heat release (THR) compared to neat PLA. TGA results showed that the PLA containing different amounts of WLA-3 presented more complicated thermal decomposition behaviours than neat PLA. Additionally, the results from DSC and tensile tests showed that the addition of WLA-3 into PLA had a slight impact on the crystallization behaviours and tensile properties.  相似文献   

13.
Poly(L ‐lactic acid) (PLLA) (? CH(CH3) ? COO? )n is a biodegradable polymer, which exhibits many applications in the biomedical field and where thermoplastics are employed. A comprehensive study of the normal modes and their dispersion in PLLA using Wilson′s GF matrix method as modified by Higgs is being reported. Assignments of calculated normal modes have been made and characteristic features of dispersion curves are discussed. Heat capacity has been calculated via density‐of‐states using Debye relation in the temperature range 10–250 K, which is in fairly good agreement with the experimental data. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 175–182, 2010  相似文献   

14.
Different proportion of nano zinc oxide (nano ZnO) and chain extender (ADR) were combined with the intumescent flame retardant and then added into the PLA matrix. The thermal stability, flame retardant performance, and mechanical properties were studied. The gel content results showed that crosslinking structures were obtained after the addition of nano ZnO and ADR, which were generated by the catalytic chain scission effect of nano ZnO and chain extension effect of ADR. With addition of 1% nano ZnO and 1.6% ADR, the gel content of flame retardant PLA composite reached the highest value (14.2%). Meanwhile, the corresponding flame retardant PLA composite with 1% nano ZnO and 1.6% ADR, named FRPLA/ZnO/ADR-1, exhibited an overall improved properties including the flame retardant properties and mechanical performance, which passed the UL94 V-0 level with a limiting oxygen index value of 40.1%. Compared to FRPLA (flame retardant PLA without ZnO and ADR), the peak heat release rate and the total smoke production of FRPLA/ZnO/ADR-1were reduced by 60% and 67% respectively, and the final mass improved from 12% to 38%. In addition, the tensile strength and elongation at break of FRPLA/ZnO/ADR-1 increased by 25%, 14% compared with that of FRPLA. The impact strength was 15.1 kJ/m2, which is similar to the pure PLA (15.6 kJ/m2). It indicated that the addition of nano ZnO and ADR could balance the flame retardant performance and the mechanical properties of the flame retardant PLA.  相似文献   

15.
In this work, phosphorylated chitosan‐coated carbon microspheres (PCH@CMS) was successfully synthesized. Obtained PCH@CMS used as flame retardant was added into unsaturated polyester resin (UPR). Fourier infrared spectroscopy (FTIR) and X‐ray electron spectroscopy (XPS) results indicated that C═O, P─O, and P═O appeared on the surface of PCH@CMS. Compared with UPR, the residues of UPR/PCH@CMS‐10 at 800°C under nitrogen and air atmospheres increased by 9.0 and 3.9 wt%, respectively, and the peak heat release rate (pHRR) and the peak smoke release rate (pSPR) of UPR/PCH@CMS‐3 decreased by 18.9% and 23.5%, respectively. Limiting oxygen index (LOI), thermogravimetric analyzer (TG), and cone calorimeter test (CCT) results showed that the addition of PCH@CMS could enhance the flame retardancy and smoke suppression of the UPR composites. Moreover, the residues after CCT were characterized by scanning electron microscopy (SEM), XPS, and laser Raman spectroscopy (LRS). Based on the above results, the flame retardant mechanism of PCH@CMS was proposed. The carbon layer produced by the UPR/PCH@CMS composites was tortuous and could suppress the heat and pyrolysis product exchange with UPR matrix.  相似文献   

16.
A series of CeO2‐loaded titania nanotubes (CeO2‐TNTs) hybrid materials with different CeO2 loadings were synthesized by co‐precipitation method and then incorporated into epoxy resin (EP) to prepare CeO2‐TNTs flame‐retardant epoxy nanocomposites. Structure and morphology characterization indicated the successful synthesis of CeO2‐TNTs. The effect of CeO2‐TNTs with different CeO2 loading capacity on the flame retardance of EP was compared and analyzed by the thermogravimetric analysis, Cone and Raman. The results showed that CeO2 loading could increase the carbon residue of nanocomposites, reduce the peak heat release rate (PHRR) and total heat release (THR), and improve the fire safety of EP. The residual carbon content of EP/0.1CeO2‐TNTs sample at 700°C reached 19.8% with the lowest degradation rate, and the PHRR and THR were reduced to 680 kW/m2 and 32.9 MJ/m2, respectively. Such a significant improvement in flame‐retardant properties for EP could be attributed to the protective effect of CeO2‐TNTs.  相似文献   

17.
A blend of two biodegradable and semi‐crystalline polymers, poly (L‐lactic acid) (PLLA; 70 wt%) and poly (butylene succinate‐co‐L‐lactate) (PBSL; 30 wt%), was prepared in the presence of various polyethylene oxide‐polypropylene oxide‐polyethylene oxide (PEO‐PPO‐PEO) triblock copolymer contents (0.5, 1, 2 wt%). Mechanical, thermal properties, and Fourier transform infrared (FTIR) analysis of the blends were investigated. It was found that the addition of copolymer to PLLA/PBSL improved the fracture toughness of the blends as shown by mode I fracture energies. It was supported by morphological analysis where the brittle deformation behavior of PLLA changed to ductile deformation with the presence of elongated fibril structure in the blend with copolymer system. The glass transition temperature (Tg), melting temperature (Tm) of PLLA, and PBSL shift‐closed together indicated that some compatibility exists in the blends. In short, PEO‐PPO‐PEO could be used as compatibilizer to improve the toughness and compatibility of the PLLA/PBSL blends. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

18.
To create a novel vector for specifically delivering anticancer therapy to solid tumors, we used diafiltration to synthesize pH‐sensitive polymeric micelles. The micelles, formed from a tetrablock copolymer [poly(ethylene glycol)‐b‐poly(L ‐histidine)‐b‐poly(L ‐lactic acid)‐b‐poly(ethylene glycol)] consisted of a hydrophobic poly(L ‐histidine) (polyHis) and poly(L ‐lactic acid) (PLA) core and a hydrophilic poly(ethylene glycol) (PEG) shell, in which we encapsulated the model anticancer drug doxorubicin (DOX). The robust micelles exhibited a critical micellar concentration (CMC) of 2.1–3.5 µg/ml and an average size of 65–80 nm pH 7.4. Importantly, they showed a pH‐dependent micellar destabilization, due to the concurrent ionization of the polyHis and the rigidity of the PLA in the micellar core. In particular, the molecular weight of PLA block affected the ionization of the micellar core. Depending on the molecular weight of the PLA block, the micelles triggering released DOX at pH 6.8 (i.e. cancer acidic pH) or pH 6.4 (i.e. endosomal pH), making this system a useful tool for specifically treating solid cancers or delivering cytoplasmic cargo in vivo. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

19.
Honeycomb monolith structured porous poly (L‐lactic acid, PLA) was simply fabricated by employing a unidirectional freeze‐casting technique. Dimethyl sulfoxide (DMSO) was used as a solvent for PLA, and the solution was unidirectionally frozen. The DMSO was nucleated in the solution and was grown in the freezing direction. The PLA was solidified and structured with the DMSO crystal as a template. Then DMSO was leached by water, ethanol, or the mixture of them, and subsequently the porous PLA was dried by oven. It was found that the freeze‐casting protocol can significantly influence the morphological features such as the tube diameter and wall thickness of tube can be tuned by varying of PLA concentration, freezing temperature, and the nature of leaching solvent. Because DMSO has a special solubility of a number of polymers, this method may be a general way for designing and preparing aligned porous materials. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

20.
A nucleating agent, benzyl‐hydrazide‐derivatized poly(lactic acid) (PLA) and γ‐cyclodextrin inclusion complex (PLA‐IC‐BH), was synthesized through a series of reactions. Poly(lactic acid) and γ‐cyclodextrin inclusion complex (PLA‐IC) was first obtained by ultrasonic co‐precipitation, which was then subjected to carboxylation, acylation, and amidation using benzoyl hydrazine and thionyl chloride. The composition and structure of PLA‐IC‐BH was confirmed by 1H nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction. PLA/PLA‐IC‐BH composites were prepared by melt blending and a hot‐press forming process. Mechanical properties, thermal stabilities, and crystallization behaviors of PLA/PLA‐IC‐BH samples were investigated by thermogravimetric analysis, differential scanning calorimetry (DSC), polarized optical microscopy (POM), rheological analysis, and so on. Mechanical testing and thermogravimetric analysis showed that the tensile strengths, impact properties, and thermal stabilities of PLA/PLA‐IC‐BH composites were improved significantly compared to pure PLA and PLA/PLA‐IC. DSC results showed that crystallinity of PLA was increased from 5.17% to 38.93% after introduction of PLA‐IC‐BH. POM results showed that PLA‐IC‐BH acted as a nucleating agent for PLA and enhanced its crystallization rate. Rotational rheological behaviors of PLA/PLA‐IC‐BH demonstrated that incorporation of PLA‐IC‐BH increased the rigidity of the network structure of the PLA matrix. Compared to those of PLA, the maximum torque and apparent viscosity of PLA/PLA‐IC‐BH composites were increased by 55.56% and 25.59%, respectively. Copyright © 2017 John Wiley & Sons, Ltd.  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