Biocomposites based on ramie fibers and poly(L‐lactic acid) (PLLA): morphology and properties

We herein report effects of morphology of PLLA and natural fiber on combination properties of biocomposites based on PLLA and ramie fibers. For this purpose, short ramie fiber (FIB), ramie fabric (FAB), PLLA film (FPLLA), and PLLA powder (PPLLA) were used to investigate the structure–property relationship of PLLA biocomposites with 30 wt% ramie fiber prepared by hot compression molding. It is revealed that mechanical properties of biocomposites are strongly dependent on the morphology of PLLA and FAB. DMA test shows that the improved storage modulus was due to the better dispersion of FIB. DSC and POM tests show that PLLA/FIB biocomposites have the highest spherulite growth rate. TGA test shows that char residue at high temperature is affected by the dispersion of PLLA and ramie fiber. SEM images exhibit the different interfacial adhesion character of FIB and FAB in the PLLA matrix after the ramie fiber treated with alkali and silane. PLLA/FAB biocomposites have not only better anti‐dripping properties when burning but also better aging resistance in UV‐irradiation hydrothermal aging, and which can be attributed to fiber bundle and laminated PLLA biocomposites structure. Copyright © 2010 John Wiley & Sons, Ltd.     

Properties and hydrolysis of PLGA and PLLA cross-linked with electron beam radiation

Radiation has been used as a processing tool to modify the properties of polymers. The aim of this study is to understand how electron beam radiation, together with pentaerythritol tetraacrylate (PTTA) as a tetra-functional monomer, can alter the properties (i.e. thermal and mechanical) and hydrolysis rates of PLGA and PLLA. The effects of radiation dose and PFM concentration on the physical properties of the polymers were investigated. The results showed that upon irradiation PLGA and PLLA cross-linked, and an increased in gel content was observed. Glass transition temperature (T_g) and mechanical properties of the polymers also increased. Cross-linked PLGA and PLLA samples were found to retard hydrolytic degradation. The mechanical properties of these polymers were also unaffected by hydrolysis. In summary, PLGA and PLLA cross-linked with PTTA were found to have enhanced mechanical properties and were able to retard hydrolytic degradation.     

Thermal and crystallization behaviour of gamma irradiated PLLA

Structure, crystallization behaviour and some thermal properties of poly-l-lactide (PLLA), gamma irradiated up to 300 kGy, have been studied. Through differential scanning calorimetry measurements, radiation-induced changes were evident in the enthalpy of melting and cold crystallization, as well as in the degree of crystallinity. Decay of the glass transition, cold crystallization and melting temperatures with irradiation dose was observed in all cases. The annealing treatment, which can substantially reduce the concentration of free radicals, also had a great impact on thermal/crystallization behaviour of irradiated PLLA. Extensive chain scission, as a dominant effect of gamma irradiation, confirmed by gel permeation chromatography, has as a consequence a growth of new thin crystal lamellae and occurrence of the second low-temperature melting peak. Thermogravimetric analyses have shown that irradiation lowered the thermal stability of PLLA.     

Preparation of waterborne polyurethane nanocomposites: Polymerization from functionalized hydroxyapatite

We report the preparation and characterization of waterborne polyurethane (WBPU)/hydroxyapatite (HAp) nanocomposites through in situ polymerization from functionalized HAp. The HAp nanoparticles (HAp NPs) were urethanated with 3-isocyanatemethyl-3,5,5-trimethyl-cyclohexylisocyanate (isophorone diisocyanate) to obtain grafted HAp NPs containing isocyanate groups (HAp-g-NCO) as crosslinkers and then the HAp-g-NCO is further polymerized with WBPU monomers to form the WBPU/HAp nanocomposites. The HAp NPs were homogeneously dispersed in the polyurethane matrix at low loading levels (?2.0 wt%), thus the mechanical strength and the elongation at break of the WBPU/HAp nanocomposites were significantly improved. Thermal stability and water resistance of the WBPU/HAp nanocomposites are also enhanced. These results suggest that the WBPU/HAp nanocomposites prepared by in situ polymerization hold the potential as new materials with improved mechanical properties, thermal stability and water resistance.     

Crystallization,rheological, and mechanical properties of PLLA/PEG blend with multiwalled carbon nanotubes

Functionalized multiwalled carbon nanotubes (FMWCNTs) were introduced into poly(L‐lactide)/polyethylene glycol (PLLA/PEG) blend and the effects of FMWCNTs on crystallization behaviors, rheological, and mechanical properties of PLLA/PEG/FMWCNTs were investigated. The results show that FMWCNTs exhibit good distribution in the nanocomposites and absorb some PEG to agglomerate around them. The crystallization behavior of PLLA in the nanocomposites is greatly dependent on the content of FMWCNTs. At low content of FMWCNTs, the addition of FMWCNTs improves the crystallization behavior of PLLA by enhancing the crystallization temperature and accelerating the crystallization rate, whereas at high content of FMWCNTs, the crystallization of PLLA is restricted to a certain degree. Rheological properties show the formation of the network structure of FMWCNTs at high content, which is the main reason for the retarded crystallization behavior of PLLA due to the network structure providing restriction to mobility and diffusion of PLLA chains to crystal growth fronts. The mechanical properties show that FMWCNTs exhibit reinforcement effect for plasticized PLLA. Copyright © 2010 John Wiley & Sons, Ltd.     

The chiral effects on the responses of osteoblastic cells to the polymeric substrates

In order to study the chiral effects of polylactides on responses of osteoblastic cells, poly(l-lactide) (PLLA), poly(d-lactide) (PDLA), poly(dl-lactide) (PDLLA) and the stereocomplex of PLLA and PDLLA (SC) films with different stereoforms were prepared. The surface properties of the four polylactide films were tested and the osteoblastic ROS 17/2.8 cells were cultured on the films. The protein adsorption behaviors of fibrinogen and bovine serum albumin on films were studied. The cell proliferation, total protein amount, DNA content and alkaline phosphatase activity of osteoblastic ROS 17/2.8 cells were evaluated. The results showed that the protein adsorption was dependant on the type of proteins. The observation of cell morphologies revealed that the PDLA film provide an unfavorable surface for cell attachment. The total protein amount, DNA content and ALP activity were closely related to the stereoforms of polylactide films. All the levels of total protein amount, DNA content and ALP activity of ROS 17/2.8 cells on PDLA film were decreased. The racemic stereocomplex of PLLA and PDLA showed relatively higher positive effects on both cell growth and proliferation.     

Toughening modification of PLLA with PCL in the presence of PCL‐b‐PLLA diblock copolymers as compatibilizer

To obtain an effective compatibilizer for the blends of poly(L‐lactide) (PLLA) and poly(ε‐caprolactone) (PCL), the diblock copolymers PCL‐b‐PLLA with different ratios of PCL/PLLA (CL/LA) and different molecular weights (M_n) were synthesized by ring‐opening polymerization (ROP) of L‐lactide with monohydric poly(ε‐caprolactone) (PCL‐OH) as a macro‐initiator. These copolymers were melt blended with PLLA/PCL (80/20) blend at contents between 3.0 and 20 phr (parts per hundred resin), and the effects of added PCL‐b‐PLLA on the mechanical, morphological, rheological, and thermodynamic properties of the PLLA/PCL/PCL‐b‐PLLA blends were investigated. The compatibility between PLLA matrix and PCL phase was enhanced with decreasing in CL/LA ratios or increasing in M_n for the added PCL‐b‐PLLA. Moreover, the crystallinity of PLLA matrix increased because of the added compatibilizers. The PCL‐b‐PLLA with the ratio of CL/LA (50/50) and M_n ≥ 39.0 kg/mol were effective compatibilizers for PLLA/PCL blends. When the content of PCL‐b‐PLLA is greater than or equal to 5 phr, the elongations at break of the PLLA/PCL/PCL‐b‐PLLA blends all reached approximately 180%, about 25 times more than the pristine PLLA/PCL(80/20) blend.     

Preparation and characterization of nano‐platelet‐like hydroxyapatite/gelatin nanocomposites

Nature has succeeded in creating numerous bionanocomposites such as bones and teeth consisting of nano‐platelets and biopolymers. Understanding of the mechanisms of formation and of the relation between structure and properties is vital for development of new materials for biomedical and engineering applications. In this work, varying contents of nano‐platelet‐like hydroxyapatite (HAp) has been used to reinforce gelatin (Gel) to produce nanocomposites. The prepared HAp/Gel nanocomposites were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric (TG/DTG) analyses. XRD, TEM, and FTIR results confirm the synthesis of intercalated and exfoliated nanostructures depending on the amount of gelatin. TG results reveal that the intercalated HAp/gelatin nanocomposites show improved thermal properties as compared to pristine gelatin. The results reported here can be expanded to other HAp–polymer systems, thus paving a new way of designing and fabricating biomemitic nanocomposites for future engineering and particularly for biomedical applications. Copyright © 2010 John Wiley & Sons, Ltd.     

Improvement in toughness of poly(l-lactide) (PLLA) through reactive blending with acrylonitrile-butadiene-styrene copolymer (ABS): Morphology and properties

Poly(l-lactide) (PLLA) was melt-blended with acrylonitrile-butadiene-styrene copolymer (ABS) with the aim of enhancing impact strength and elongation at break of PLLA, but not sacrificing its modulus and stiffness significantly. However, PLLA and ABS were found to be thermodynamically immiscible by simply melt blending and the formed blends show deteriorated mechanical properties. The reactive styrene/acrylonitrile/glycidyl methacrylate copolymer (SAN-GMA) by incorporating with ethyltriphenyl phosphonium bromide (ETPB) as the catalyst was used as the in situ compatibilizer for PLLA/ABS blends to improve the compatibility between PLLA and ABS. The reactive process during melt blending was investigated by Fourier transformed infra-red (FTIR). It showed that the epoxide group of SAN-GMA reacted with PLLA end groups under the mixing conditions and that the addition of ETPB accelerated the reaction. Phase structure and physical properties of the compatibilized blends were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic mechanical analysis (DMA), tensile tests and impact property measurements. It was found that the size of ABS domains in PLLA matrix is significantly decreased by addition of the reactive compatibilizer. The dynamic mechanical analysis revealed markedly shifted glass transition temperatures for both PLLA and ABS, indicating the improved compatibility between PLLA and ABS. The mechanical tests showed the compatibilized PLLA/ABS blends had a very nice stiffness-toughness balance, i.e., the improved impact strength and the elongation at break with a slightly loss in the modulus.     

Poly(l‐Lactic Acid)/Gelatin Fibrous Scaffold Loaded with Simvastatin/Beta‐Cyclodextrin‐Modified Hydroxyapatite Inclusion Complex for Bone Tissue Regeneration

Recently, the application of nanostructured materials in the field of tissue engineering has garnered attention to mediate treatment and regeneration of bone defects. In this study, poly(l ‐lactic acid) (PLLA)/gelatin (PG) fibrous scaffolds are fabricated and β‐cyclodextrin (βCD) grafted nano‐hydroxyapatite (HAp) is coated onto the fibrous scaffold surface via an interaction between βCD and adamantane. Simvastatin (SIM), which is known to promote osteoblast viability and differentiation, is loaded into the remaining βCD. The specimen morphologies are characterized by scanning electron microscopy. The release profile of SIM from the drug loaded scaffold is also evaluated. In vitro proliferation and osteogenic differentiation of human adipose derived stem cells on SIM/HAp coated PG composite scaffolds is characterized by alkaline phosphatase (ALP) activity, mineralization (Alizarin Red S staining), and real time Polymerase chain reaction (PCR). The scaffolds are then implanted into rabbit calvarial defects and analyzed by microcomputed tomography for bone formation after four and eight weeks. These results demonstrate that SIM loaded PLLA/gelatin/HAp‐(βCD) scaffolds promote significantly higher ALP activity, mineralization, osteogenic gene expression, and bone regeneration than control scaffolds. This suggests the potential application of this material toward bone tissue engineering.

     

Structure and mechanical properties of poly(l-lactide)/layered silicate nanocomposites

Poly(ε-caprolactone) (PCL) masterbatches with the intercalated and the exfoliated morphology were prepared by ring opening polymerization of ε-caprolactone in the presence of organomodified montmorillonite (MMT) Cloisite 30B. Poly(l-lactide) (PLLA) nanocomposites with Cloisite 30B or PCL masterbatches were prepared by melt blending. The effects of the silicate type, MMT content and the nanocomposite morphology on thermal and mechanical properties of PLLA nanocomposites were examined. The montmorillonite particles in PLLA/Cloisite 30B and PLLA/intercalated masterbatch nanocomposites were intercalated. In contrary to expectations, the exfoliated silicate layers of exfoliated masterbatch were not transferred into the PLLA matrix. Due to a low miscibility of PCL and PLLA, MMT remained in the phase-separated masterbatch domains. The stress-strain characteristics of PLLA nanocomposites, Young modulus E, yield stress σ_y and yield strain ε_y, decreased with increasing MMT concentration, which is associated with the increase in PCL content. The expected stiffening effect of MMT was low due to a low aspect ratio of its particles and was obscured by both plastifying effects of PCL and low PLLA crystallinity. Interestingly, in contrast to the neat PLLA, ductility was enhanced in all PLLA/Cloisite 30B materials and in PLLA/masterbatch nanocomposites with low MMT concentrations.     

Influence of crystal polymorphism on mechanical and barrier properties of poly(l-lactic acid)

The effect of crystal polymorphism on barrier and mechanical properties of PLLA is detailed in this contribution. PLLA films containing different amounts of α and α′ crystal forms were prepared by annealing quenched PLLA at different temperatures. The polymorphic structure of the films was analyzed by X-ray diffraction. Mechanical properties and permeability to water vapor were investigated as a function of degree of crystallinity (w_C) and related to crystal polymorphism developed during annealing. The polymorphic structure of PLLA significantly affects mechanical and barrier properties. The α crystal modification provides a better barrier to water vapor and a higher Young’s modulus, compared to films containing the α′ modification, but a lower elongation at break. The varied barrier and mechanical properties were correlated to the different packing of PLLA chains in the two analyzed polymorphs. The conformational disorder of the α′ form makes this structure a mesophase (condis crystal), with remarkable effects on material properties.     

Comparative study of poly(L‐lactide) nanocomposites with organic montmorillonite and carbon nanotubes

Organic montmorillonite (OMMT) and the one‐dimensional functionalized multiwalled carbon nanotubes (FMWCNTs) were introduced into poly(L ‐lactide) (PLLA) to prepare PLLA/OMMT and PLLA/FMWCNT nanocomposites, respectively. The effects of nanofillers on melt crystallization and cold crystallization of PLLA were comparatively investigated by using polarized optical microcopy, differential scanning calorimetry and wide angle X‐ray diffraction. The results show that FMWCNTs exhibit higher nucleation efficiency for the melt crystallization of PLLA, whereas OMMT is the better one for the cold crystallization of PLLA. Rheological properties show that both OMMT and FMWCNTs at relatively higher concentrations can form the percolated network structure in the PLLA matrix, however, the latter nanocomposites exhibit relatively denser or more compact percolated networks. The difference of the networks between OMMT and FMWCNTs is suggested to be the main reason for the different cold crystallization behaviors observed in the PLLA/OMMT and PLLA/FMWCNT nanocomposites. The dynamic mechanical analysis measurements show that OMMT is the better one to improve the stiffness of the nanocomposites in the present work. The thermogravimetric analysis measurements show that FMWCNTs have higher efficiency in improving the thermal stability of PLLA compared with OMMT. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Toughening of poly(L‐lactide)/multiwalled carbon nanotubes nanocomposite with ethylene‐co‐vinyl acetate

Poly(L ‐lactide)/multiwalled carbon nanotubes (PLLA/MWCNTs) nanocomposite recently attracts much attention because of its excellent comprehensive properties including improved thermostability, tensile strength, and conductivity. However, the nanocomposite exhibits similar brittleness compared with unmodified PLLA. In this work, a polar elastomer, that is, ethylene‐co‐vinyl acetate (EVA), was introduced into PLLA/MWCNTs nanocomposite. The selective distribution of MWCNTs and the effects of EVA on crystalline structure of PLLA were investigated using scanning electron microscope, transmission electron microscope, differential scanning calorimetry, and wide angle X‐ray diffraction. The results show that the presence of EVA induces the change of the distribution of MWCNTs in the nanocomposites, and consequently, the cold crystallization of PLLA is prevented. With the increase of EVA content, both the ductility and the impact resistance of PLLA/FMWCNTs are improved greatly, indicating the toughening effect of EVA on PLLA/MWCNTs nanocomposite. The decreased tensile strength and modulus can be compensated through annealing treatment. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

溶剂诱导的聚乳酸/聚乳酸衍生物共结晶行为

通过溶液浇铸法制备不同组分的左旋聚乳酸(PLLA)和聚(L-2-羟基-3-甲基丁酸)(PL-2H3MB)共混物.运用差示扫描量热仪(DSC)、偏光显微镜(POM)、广角X射线衍射(WAXD)和热重分析仪(TGA)分析共混物的结晶、熔融行为和热稳定性.通过观察到DSC加热曲线中新的熔融峰判断PLLA和PL-2H3MB共晶...     

Cell adhesive and growth behavior on electrospun nanofibrous scaffolds by designed multifunctional composites

Nanostructured biocomposite scaffolds of poly(l-lactide) (PLLA) blended with collagen (coll) or hydroxyapatite (HA), or both for tissue engineering application, were fabricated by electrospinning. The electrospun scaffolds were characterized for the morphology, chemical and tensile properties by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA), Fourier transform infrared (FTIR) measurement, and tensile testing. Electrospun biocomposite scaffolds of PLLA and collagen or (and) HA in the diameter range of 200-700 nm mimic the nanoscale structure of the extracellular matrix (ECM) with a well-interconnection pore network structure. The presence of collagen in the scaffolds increased their hydrophility, and enhanced cell attachment and proliferation, while HA improved the tensile properties of the scaffolds. The biocompatibility of the electrospun scaffolds and the viability of contacting cells were evaluated by 4',6-diamidino-2-phenylindole dihydrochloride (DAPI) nuclear staining and by fluorescein diacetate (FDA) and propidium iodide (PI) double staining methods. The results support the conclusion that 293T cells grew well on composite scaffolds. Compared with pure PLLA scaffolds a greater density of viable cells was seen on the composites, especially the PLLA/HA/collagen scaffolds.     

Preparation and characterization of polyoxymethylene‐copolymer/hydroxyapatite nanocomposites for long‐term bone implants

In this work, new polyoxymethylene (POM)/hydroxyapatite (HAp) nanocomposites for long‐term bone implants have been obtained via extrusion and injection molding processes and characterized by differential scanning calorimetry (DSC), temperature‐modulated DSC (TMDSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), wide‐angle X‐ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), and tensile mechanical and in vitro stability tests. Based on the DSC results, it was found that the degree of crystallinity increases for POM/0.5% HAp sample and decreases for POM/1.0% HAp and POM/2.5% HAp. SEM and TEM observations for POM/HAp nanocomposites indicated that the dispersion of HAp in the polymer matrix was uniform and the diameter of the HAp particles was less than 100 nm for most of them. Young's modulus increases with increasing HAp concentration, whereby elongation at break decreases. On the contrary, HAp concentration does not have a significant influence on the tensile strength. TG results show that for POM/0.5% HAp, POM/1.0% HAp, and POM/2.5% HAp, thermal stability slightly increases in comparison to pure POM, whereas for POM/5.0 HAp and POM/10.0% HAp, lower thermal stability was observed. In vitro data reveal that with an increase of HAp content, bioactivity of nanocomposites increases; a good in vitro chemical stability of POM and POM nanocomposites was confirmed. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of MA-g-PP and lignocellulosic filler addition on several properties of poly(L-lactic acid)/polypropylene composites

The aim of this study was to investigate the effects of maleic anhydride-graft-polypropylene (MA-g-PP) as a compatibilizer and wood fiber as a lignocellulosic filler on technical properties of poly(l-lactic acid) (PLLA)/polypropylene composites. The obtained composites were characterized through mechanical tests, thermogravimetric analysis, differential scanning analyzer, and chemical analysis via Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). The obtained results showed that the mechanical properties of the composites containing MA-g-PP were higher than those of the composites without MA-g-PP. SEM images revealed that the morphological properties of the composites including PP and PLLA were improved. The chemical interactions between PP and PLLA were demonstrated through FTIR results of composites with MA-g-PP.     

Electrospun Aligned Poly(L-lactide)/Poly(ϵ-caprolactone) /Poly(ethylene glycol) Blend Fibrous Membranes

Aligned poly(L-lactide) (PLLA)/poly(?-caprolactone) (PCL)/poly(ethylene glycol)(PEG) fibrous membranes were fabricated by electrospinning. Their morphology, thermal stability, mechanical properties, hydrophilic properties and in vitro degradation behaviors were investigated. With increasing the content of PEG, the PLLA/PCL/PEG blend fibers become thinner due to the increment in solution conductivity and decrease in solution viscosity. The thermal stability, hydrophilic properties, the tensile strength and elongation-at-break of PLLA/PCL/PEG blend fibrous membranes were improved, but porosity were decreased with the content of PEG changing from 10 wt% to 30 wt%. Furthermore, the incorporation of PEG enhanced the degradation of the PLLA/PCL/PEG fibrous membranes due to the better hydrophilic properties. In addition, the PLLA/PCL/PEG fibrous membranes have no toxic effect on proliferation of adipose-derived stem cells.     

Systematic investigation and in vitro biocompatibility studies on mesoporous europium doped hydroxyapatite

This paper reports the systematic investigation of europium doped hydroxyapatite (Eu:HAp). A set of complementary techniques, namely Fourier Transform Infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and the Brunauer-Emmett-Teller (BET) technique were used towards attaining a detailed understanding of Eu:HAp. The XPS analysis confirmed the substitution of Ca ions by Eu ions in the Eu:HAp samples. Secondly, Eu:HAp and pure HAp present type IV isotherms with a hysteresis loop at a relative pressure (P/P₀) between 0.4 and 1.0, indicating the presence of mesopores. Finally, the in vitro biological effects of Eu:HAp nanoparticles were evaluated by focusing on the F-actin filament pattern and heat shock proteins (Hsp) expression in HEK293 human kidney cell line. Fluorescence microscopy studies of the actin protein revealed no changes of the immunolabelling profile in the renal cells cultured in the presence of Eu:HAp nanoparticles. Hsp60, Hsp70 and Hsp90 expressions measured by Western blot analysis were not affected after 24 and 48 hours exposure. Taken together, these results confirmed the lack of toxicity and the biocompatibility of the Eu:HAp nanoparticles. Consequently, the possibility of using these nanoparticles for medical purposes without affecting the renal function can be envisaged.