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1.
In the first part of this article, we reported the crystalline memory effect on the nonisothermal crystallization of poly(L ‐lactide). The experiments were carried out by using polymer single crystals growth from dilute solution as standard starting material. In this article (Part II), we have analyzed in detail the effect of the melting condition on the overall crystallization kinetics by applying the Nakamura‐Avrami model to DSC results. The absence or the low concentration of foreign infusible heterogeneous nuclei in our system allowed us to exalt the self‐nuclei role in polymer crystallization, to follow their concentration decrease during the melting process and to find the limiting melting temperature for their disappearance. Below such a temperature, a stable equilibrium number of self‐nuclei was observed, probably deriving from ordered structures, persisting in the melt, and originated from the single crystals thickening process during the polymer dynamic melting in the DSC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   

2.
BACKGROUND: Poly(para‐dioxanone) (PPDO) is a biodegradable polyester with excellent biodegradability, bioabsorbability, biocompatibility and mechanical flexibility. However, its high cost and relatively fast degradation rate have hindered the development of commercial applications. Blending with other polymers is a simple and convenient way of modifying the properties of aliphatic polyesters. Poly(D ,L ‐lactide) (PDLLA) is another polyester that has been extensively studied for biomedical applications due to its biocompatibility and suitable degradation rate. However, to our knowledge, blends of PPDO/PDLLA have not been reported in the literature. RESULTS: A series of biodegradable polymers were blended by solution co‐precipitation of PPDO and PDLLA in various blend ratios. The miscibility, morphology and thermal properties of the materials were investigated. DSC curves for all blends revealed two discrete glass transition temperatures which matched the values for pure PPDO and PDLLA. SEM images of fracture surfaces displayed evidence of phase separation consistent with the DSC results. The contact angles increased with the addition of PDLLA. CONCLUSION: PPDO/PDLLA blends exhibit two distinct glass transition temperatures that remain nearly constant and correspond to the glass transition temperatures of the homopolymers for all blend compositions, indicating that blends of PPDO and PDLLA are immiscible. Images of the surface obtained using SEM were also suggestive of a two‐phase material. The crystallinity of the PPDO phase in the blends was affected by the PDLLA content. The mechanical properties of the blends changed dramatically with composition. Adding PDLLA makes the blends less hydrophilic than PPDO. Copyright © 2008 Society of Chemical Industry  相似文献   

3.
A silane‐grafting water‐crosslinking approach was developed to crosslink poly(L ‐lactide) (PLLA) by grafting vinylalkoxysilane onto PLLA using dicumyl peroxide, followed by silane hydrolysis to form siloxane linkages between PLLA chains. The degree of silane grafting onto PLLA was qualitatively characterized using Fourier transform infrared spectroscopy and quantitatively determined using inductively coupled plasma mass spectrometry. Crosslinked PLLA films were obtained by curing of silane‐grafted PLLA in hot water. Gel fractions were evaluated in order to calculate the crosslinking reaction kinetics and crosslinking density. Various techniques were used to investigate the effect of silane water‐crosslinking on the thermomechanical properties, hydrolysis resistance and biodegradation of PLLA. In addition to an improvement in thermal stability and mechanical properties, hydrolysis resistance was significantly enhanced as a result of silane water‐crosslinking of PLLA. Moreover, the biodegradation of silane water‐crosslinked PLLA was retarded compared with neat PLLA. Copyright © 2010 Society of Chemical Industry  相似文献   

4.
Poly(L‐lactide)‐poly(ethylene glycol) multiblock copolymers with predetermined block lengths were synthesized by polycondensation of PLA diols and PEG diacids. The reaction was carried out under mild conditions, using dicyclohexylcarbodiimide as the coupling agent and dimethylaminopyridine as the catalyst. The resulting copolymers were characterized by various analytical techniques, such as GPC, viscometry, 1H‐NMR, FTIR, DSC, X‐ray diffractometry, and contact angle measurement. The results indicated that these copolymers presented outstanding properties pertinent to biomedical use, including better miscibility between the two components, low crystallinity, and hydrophilicity. Moreover, the properties of the copolymers can be modulated by adjusting the block length of the two components or the reaction conditions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1729–1736, 2002; DOI 10.1002/app.10580  相似文献   

5.
Optically active poly(L ‐phenyllactic acid) (Ph‐PLLA), poly(L ‐lactic acid) (PLLA), and poly(L ‐phenyllactic acid‐co‐L ‐lactic acid) with weight‐average molecular weight exceeding 6 × 103 g mol?1 were successfully synthesized by acid catalyzed direct polycondensation of L ‐phenyllactic acid and/or L ‐lactic acid in the presence of 2.5–10 wt % of p‐toluenesulfonic acid. Their physical properties and crystallization behavior were investigated by differential scanning calorimetry, thermogravimetry, and polarimetry. The absolute value of specific optical rotation ([α]) for Ph‐PLLA (?38 deg dm?1 g?1 cm3) was much lower than that of [α] for PLLA (?150 deg dm?1 g?1 cm3), suggesting that the helical nature was reduced by incorporation of bulky phenyl group. PLLA was crystallizable during solvent evaporation, heating from room temperature, and cooling from the melt. Incorporation of a very low content of bulky phenyllactyl units even at 4 mol % suppressed the crystallization of L ‐lactyl unit sequences during heating and cooling, though the copolymers were crystallizable for L ‐phenylactyl units up to 6 mol % during solvent evaporation. The activation energy of thermal degradation (ΔEtd) for Ph‐PLLA (200 kJ mol?1) was higher than that for PLLA (158 kJ mol?1). The ΔEtd for the copolymers increased with an increase in L ‐phenyllactyl unit content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

6.
The crystalline structure of poly(L ‐lactide) (PLLA) have been found to quite depend on the crystallization temperatures (Tcs), especially in the range of 100?120°C, which is usually used as the crystallization temperature for the industrial process of PLLA. The analysis of wide‐angle X‐ray diffraction and Fourier transformed infrared spectroscopy revealed that 110°C is a critical temperature for PLLA crystallization. At Tc < 110°C and Tc ≥ 110°C, the α′ and α crystals were mainly produced, respectively. Besides, the structural feature of the α′‐form was illustrated, and it was found that the α′‐form has the larger unit cell dimension than that of the α‐form. Moreover, the crystallization kinetics of the α′ and α crystals are different, resulting in the discontinuousness of the curves of spherulite radius growth rate (G) versus Tc and the half time in the melt‐crystallization (t1/2) versus Tc investigated by Polarized optical microscope and Differential scanning calorimetry, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

7.
Blended films of poly(L ‐lactide) [ie poly(L ‐lactic acid)] (PLLA) and poly(?‐caprolactone) (PCL) without or mixed with 10 wt% poly(L ‐lactide‐co‐?‐caprolactone) (PLLA‐CL) were prepared by solution‐casting. The effects of PLLA‐CL on the morphology, phase structure, crystallization, and mechanical properties of films have been investigated using polarization optical microscopy, scanning electron microscopy, differential scanning calorimetry and tensile testing. Addition of PLLA‐CL decreased number densities of spherulites in PLLA and PCL films, and improved the observability of spherulites and the smoothness of cross‐section of the PLLA/PCL blend film. The melting temperatures (Tm) of PLLA and PCL in the films remained unchanged upon addition of PLLA‐CL, while the crystallinities of PLLA and PCL increased at PLLA contents [XPLLA = weight of PLLA/(weight of PLLA and PCL)] of 0.4–0.7 and at most of the XPLLA values, respectively. The addition of PLLA‐CL improved the tensile strength and the Young modulus of the films at XPLLA of 0.5–0.8 and of 0–0.1 and 0.5–0.8, respectively, and the elongation at break of the films at all the XPLLA values. These findings strongly suggest that PLLA‐CL was miscible with PLLA and PCL, and that the dissolved PLLA‐CL in PLLA‐rich and PCL‐rich phases increased the compatibility between these two phases. © 2003 Society of Chemical Industry  相似文献   

8.
Triacetin (TAC) is known as a lubricant of poly(L ‐lactide) (PLLA), and it is used to improve the mechanical properties of PLLA. However, the compatibility of TAC with PLLA and the morphological changes induced by the addition of TAC to PLLA have not been clarified. This study investigates the effects of the addition of TAC on the morphological changes and physical properties of PLLA. We prepared the PLLA films containing a given amount of TAC by solvent‐cast blending with chloroform under a low temperature. From the investigation of the mechanical properties of the blends, it is found that the glass‐transition temperature of PLLA is remarkably decreased with an increasing amount of TAC, the blend films exhibit high elastic recovery, and the degree of the recovery increases linearly with the amount of TAC. The morphological changes exhibiting high elastic recovery are discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 474–480, 2003  相似文献   

9.
Amorphous poly(L ‐lactide) (PLLA) composite films with titanium dioxide (TiO2) particles were prepared by solution‐casting using methylene chloride as a solvent, followed by quenching from the melt. The effects of surface treatment, volume fraction, size, and crystalline type of the TiO2 particles on the mechanical properties and enzymatic hydrolysis of the composite films were investigated. The tensile strength of the PLLA composite films containing TiO2 particles except for anatase‐type ones with a mean particle size of 0.3–0.5 μm was lowered and the Young's modulus became higher with increasing the content of TiO2 particles. The tensile strength of the composite films containing anatase‐type TiO2 with a mean particle size of 0.3–0.5 μm at contents of 20 wt % or less was almost the same as that of the pure PLLA film. The enzymatic hydrolysis of PLLA matrix was accelerated by the addition of the hydrophilic anatase‐type TiO2 particles (nontreated or Al2O3 treated) with a mean particle size of 0.3–0.5 μm at relatively high contents such as 20 wt %. On the other hand, the enzymatic hydrolysis of PLLA matrix was inhibited by composite formation with the hydrophobic rutile‐type TiO2 particles (Al2O3‐stearic acid treated, or ZrO2‐Al2O3‐stearic acid treated). These results suggest that the mechanical properties and enzymatic hydrolyzability of the PLLA can be controlled by the kind and amount of the added TiO2 particles. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 190–199, 2005  相似文献   

10.
Hybrids of poly(L ‐lactide)/organophilic clay (PLACHs) have been prepared by a melt‐compounding process using poly(L ‐lactide) (PLLA) and different contents of surface‐treated montmorillonite modified with a dimethyl dioctadecyl ammonium salt. The dispersion structures of clay particles in PLACHs were investigated using wide‐angle X‐ray diffraction and transmission electron microscopy. The solid‐state linear viscoelastic properties for these PLACHs were examined as functions of temperature and frequency. The incorporation of organo‐modified silicate into PLLA matrix enhanced significantly both storage moduli (E′) and loss moduli (E″). The strong enhancement observed in dynamic moduli of PLACHs could be attributed to uniformly dispersed state of the clay particles with high aspect ratio (= length/thickness of clay) and the intercalation of the PLLA chains between silicate layers. Copyright © 2006 Society of Chemical Industry  相似文献   

11.
The influence of processing conditions during melt extrusion on the degradation of poly(L ‐lactide) (PLLA) has been investigated. PLLA polymer was processed by melt extrusion in a double screw extruder at 210 and 240°C. For each extrusion temperature, two screw rotation speeds, 20 and 120 rpm, were used. To investigate the influence of moisture on the thermal degradation during processing, the PLLA granules were dried at 100°C for 5 h and then either extruded directly or conditioned at 65% RH, 20°C for 24 h prior to extrusion. The results show that a decrease in molecular weight measured as number‐average (Mn) molecular weight occurs for all combinations of process parameters used. At processing temperature of 210°C, the change in molecular weight for the dry granules was shown to be dependent on the residence time (i.e., screw rotation speed) in the melt. By changing the screw rotation speed from 120 to 20 rpm at 210°C, Mn decreased from 33,600 to 30,200 g/mol. When the processing temperature was increased to 240°C, the dry granules showed an Mn of 25,600 and 13,600 g/mol when extruded at 120 and 20 rpm, respectively. Mn for the conditioned specimens extruded at 210°C was 18,400 g/mol when processed at 120 rpm and 12,300 g/mol at 20 rpm. When processed at 240°C, 20 rpm, Mn is independent of whether the granules were dry or moist prior to extrusion. It is probably due to the fact that the degradation at 240°C is so extensive that the presence of moisture in the polymer does not contribute further to the degradation process. The stress and strain at break decreased due to degradation and were dependent on the molecular weight of the samples. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2128–2135, 2001  相似文献   

12.
New biodegradable block copolymer networks were synthesized from methacrylate‐terminated poly(L ‐lactide) (mLA) and polycaprolactone (mCL) macromers. This allowed the realization of a series of materials in which the macromer ratio can be used to tailor the physical and mechanical properties of the materials. The synthesis of the macromers was characterized using Fourier transform infrared (FTIR) spectroscopy and 1H NMR spectroscopy. Poly(mCL) and poly(mLA) networks were prepared by photopolymerization of the macromers, and copolymers were also prepared from the two macromers in various proportions. The phase microstructure of the new systems and the network architecture were investigated using differential scanning calorimetry, FTIR spectroscopy, dynamic mechanical analysis and thermogravimetry studies. Copyright © 2010 Society of Chemical Industry  相似文献   

13.
Bio‐based polymer composite was successfully fabricated from plant‐derived kenaf fiber (KF) and renewable resource‐based biodegradable polyester, poly(L ‐lactide) (PLLA), by melt‐mixing technique. The effect of the KF weight contents (0, 10, 20, and 30 wt %) on crystallization behavior, composite morphology, mechanical, and dynamic mechanical properties of PLLA/KF composites were investigated. It was found that the incorporation of KF significantly improves the crystallization rate and tensile and storage modulus. The crystallization of PLLA can be completed during the cooling process from the melt at 5°C/min with the addition of 10 wt % KF. It was also observed that the nucleation density increases dramatically and the spherulite size drops greatly in the isothermal crystallization with the presence of KF. In addition, with the incorporation of 30 wt % KF, the half times of isothermal crystallization at 120°C and 140°C were reduced to 46.5% and 28.1% of the pure PLLA, respectively. Moreover, the tensile and storage modulus of the composite are improved by 30% and 28%, respectively, by the reinforcement with 30% KF. Scanning electron microscopy observation also showed that the crystallization rate and mechanical properties could be further improved by optimizing the interfacial interaction and compatibility between the KF and PLLA matrix. Overall, it was concluded that the KF could be the potential and promising filler for PLLA to produce biodegradable composite materials, owing to its good ability to improve the mechanical properties as well as to accelerate the crystallization of PLLA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007  相似文献   

14.
The effects of storage at 25°C in swelling solvents having different solubility parameter (δs) values of 16.8–26.0 J0.5 cm−1.5 on the physical properties and structure of as‐cast poly(L ‐lactide) (PLLA) films was investigated by the degree of swelling (DS), differential scanning calorimetry (DSC), and tensile tests. It was found that PLLA film shows durabity to swelling solvents having δs values much lower or higher than the value range of 19–20.5 J0.5 cm−1.5 and that the polymer solubility parameter (δp) for PLLA is in the value range of 19–20.5 J0.5 cm−1.5. The decrease in the glass transition temperature (Tg) and tensile properties and the increase in melting temperature (Tm) and crystallinity (xc) were larger for PLLA films swollen in solvents having a high DS at 7 days (DS7days). The slight increase in Tm and xc for PLLA films after swelling in solvents with high DS7days values was due to the crystallization of PLLA that occurred during swelling, while the small increase in Tg and elongation at break (εB) for PLLA films after immersion in the solvents having low DS7days values was ascribed to stabilized chain packing in the amorphous region. The Tg, εB, and Young's modulus of the PLLA films after swelling in the solvents varied in the ranges of 47–57°C, 4–8%, and 55–77 kg/mm2, depending on their DS7days or δs values. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1582–1589, 2001  相似文献   

15.
The biotic and abiotic degradation of poly (L‐lactide) (PLLA) has been studied with pyrolysis gas chromatography mass spectrometry (Py‐GC‐MS). A mixed culture of compost micro‐organisms was used as the biotic medium. Size‐exclusion chromatography (SEC), gas chromatography‐mass spectrometry (GC‐MS), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were utilized to monitor the degradation and degradation mechanism. Differences in pH, molecular weight, surface structure, and degradation mechanisms were noted between sample aged in biotic and abiotic medium. Using fractionated Py‐GC‐MS at 400 and 500°C, acetaldehyde, acrylic acid, lactoyl acrylic acid, two lactide isomers, and cyclic oligomers up to the pentamer were identified as thermal decomposition products of PLA as well as some other not completely identified products. The ratio of meso‐lactide to L‐lactide was lower in the sample aged in the biotic media than the abiotic media. This is a result of the preference of the micro‐organisms for L‐form of lactic acid and lactoyl lactic acid rather than the D‐form that in turn influences the formation and the amounts of meso and D,L‐lactide during the pyrolysis. Based on SEM micrographs, it was shown that degradation in the biotic medium proceeded mainly via a surface erosion mechanism, whereas bulk erosion was the predominant degradation mechanism in the abiotic medium. The SEC and Py‐GC‐MS data indicate that degradation was faster in the biotic than in the abiotic sample. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2369–2378, 2000  相似文献   

16.
BACKGROUND: Polymer/multi‐walled carbon nanotube (MWCNT) composites are one of the most promising alternatives to conventional polymer composites filled with micrometre‐sized fillers. This approach can also be applied for the improvement of mechanical properties and thermal stability of biodegradable aliphatic polyesters, such as poly(L ‐lactide) (PLLA), which have been receiving increasing attention due to environmental concerns. Thermal degradation behaviour provides useful information for the determination of the optimum processing conditions and for identification of potential applications of final products. RESULTS: The PLLA/MWCNT composites investigated showed a higher thermal degradation peak temperature and onset temperature of degradation along with a higher amount of residue at the completion of degradation than neat PLLA. Moreover, PLLA/MWCNT composites with a greater MWCNT content showed higher activation energy of thermal degradation than those with a lower MWCNT loading, which confirmed the positive effect of MWCNT incorporation on the enhancement of PLLA thermal stability. CONCLUSION: This study explored the thermal degradation behaviour of PLLA/MWCNT composites by observing the weight loss, molecular weight and mechanical properties during non‐isothermal and isothermal degradation. The incorporation of MWCNTs into the PLLA matrix enhanced considerably the mechanical properties and thermal stability. Copyright © 2009 Society of Chemical Industry  相似文献   

17.
The enzymatic degradation of poly(D ,L ‐lactide) (PLA) was investigated using two different lipases, Novozym 435 and Lipolase. The optimum temperature was 50°C for the enzymatic degradation of PLA. The effect of various solvents on the degradation of PLA was investigated at 50°C using Novozym 435, and toluene was found to be the best solvent among the solvents investigated. The enzymatic degradation of the blends of PLA and PVAc was investigated at 50°C in toluene. The enzymatic degradation of the blends of PLA and PVAc showed that there is an interaction between the polymers during degradation, which results in the reduction of degradation rate of both polymers in the blend. A continuous distribution model was used to determine the rate coefficients for polymer degradation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 657–680 2006  相似文献   

18.
Reaction between epoxidized natural rubber and poly(L ‐lactide) (PLLA) was investigated quantitatively in terms of conversion of the epoxidized natural rubber. The epoxidized natural rubber was prepared by epoxidation of high ammonia natural rubber (HA‐NR) or deproteinized natural rubber (DPNR) with peracetic acid followed by depolymerization with ammonium persulfate. The resulting liquid HA‐NR having epoxy group (LENR) or liquid DPNR having epoxy group (LEDPNR) were subjected to heating at 473 K for 20 min, after blending with PLLA. The products were characterized through morphology observation, DSC measurement, and 1H‐NMR spectroscopy. The conversions of the rubbers were estimated from intensity ratio of signals in 1H‐NMR spectrum for the products after removing unreacted rubber with toluene. Difference in the estimated conversion between the LENR/PLLA and LEDPNR/PLLA blends was interpreted in relation to proteins present in the rubber. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   

19.
A series of biodegradable polylactide‐based polyurethanes (PLAUs) were synthesized using PLA diol (Mn = 3200) as soft segment, 4,4′‐diphenylmethane diisocyanate (MDI), 2,4‐toluene diisocyanate (TDI), and isophorone diisocyanate (IPDI) as hard segment, and 1,4‐butanediol as chain extender. The structures and properties of these PLAUs were studied using infrared spectroscopy, differential scanning calorimetry, tensile testing, and thermomechanical analysis. Among them, the MDI‐based PLAU has the highest Tg, maximum tensile strength, and restoration force, the TDI‐based PLAU has the lowest Tg, and the IPDI‐based PLAU has the highest tensile modulus and elongation at break. They are all amorphous. The shape recovery of the three PLAUs is almost complete in a tensile elongation of 150% or a twofold compression. They can keep their temporary shape easily at room temperature (20 °C). More importantly, they can deform and recover at a temperature below their Tg values. Therefore, by selecting the appropriate hard segment and adjusting the ratio of hard to soft segments, they can meet different practical demands for shape memory medical devices. Copyright © 2007 Society of Chemical Industry  相似文献   

20.
The effect of poly(D ,L ‐lactide‐copara‐dioxanone) (PLADO) as the compatibilizer on the properties of the blend of poly(para‐dioxanone) (PPDO) and poly(D ,L ‐lactide) (PDLLA) has been investigated. The 80/20 PPDO/PDLLA blends containing from 1% to 10% of random copolymer PLADO were prepared by solution coprecipitation. The PLADO component played a very important role in determining morphology, thermal, mechanical, and hydrophilic properties of the blends. Addition of PLADO into the blends could enhance the compatibility between dispersed PDLLA phase and PPDO matrix; the boundary between the two phases became unclear and even the smallest holes were not detected. On the other hand, the position of the Tg was composition dependent; when 5% PLADO was added into blend, the Tg distance between PPDO and PDLLA was shortened. The blends with various contents of compatibilizer had better mechanical properties compared with simple PPDO/PDLLA binary polymer blend, and such characteristics further improved as adding 5% random copolymers. The maximum observed tensile strength was 29.05 MPa for the compatibilized PPDO/PDLLA blend with 5% PLADO, whereas tensile strength of the uncompatibilized PPDO/PDLLA blend was 14.03 MPa, which was the lowest tensile strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011  相似文献   

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