Effects of lipase on poly(lactic acid) fibers

Two types of lipases, L3126 and Lipex 100L, were used to modify the surface of poly(lactic acid) (PLA) fiber by measuring weight loss percentage and wettability of the fiber in this work. The influence factors were discussed and optimized based on single-factor experiments. The optimal conditions for the modification of poly(lactic acid) fiber with lipases were determined as follows: incubation with lipase L3126 of 0.5 g/l at 45 °C and pH 8.5 for 8 hours and incubation with lipase of 10 ml/l at 40 °C and pH 7.5 for 10 hours. Lipase L3126 showed higher biodegradation ability to poly(lactic acid) fiber than lipase Lipex 100L. The scanning electron microscopy confirmed that both of the two lipases could lead to the formation of etching characters on treated poly(lactic acid) fibers in comparison with the blank samples. Furthermore, the wettability of the fibers treated with the lipases was evidently improved, especially Lipase L3126.     

Effect of surface treatment of jute fibers on the interfacial adhesion in poly(lactic acid)/jute fiber biocomposites

Jute fibers have immense potential to be used as natural fillers in polymeric matrices to prepare biocomposites. In the present study jute fibers were surface treated using two methods: i) alkali (NaOH) and ii) alkali followed by silane (NaOH+Silane) separately. Effects of surface treatments on jute fibers surface were characterized using fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) analyses. Further, the effects of surface treatments on jute fibers properties such as crystallinity index, thermal stability, and tensile properties were analyzed by X-ray diffraction method (XRD), thermo gravimetric analysis (TGA), and single fiber tensile test respectively. The effects of surface treatment of jute fibers on interphase adhesion between of poly(lactic acid) (PLA) and jute fibers were analyzed by performing single fiber pull-out test and was examined in terms of interfacial shear strength (IFSS) and critical fiber length.     

Surface modification of poly(lactic acid) by UV/Ozone irradiation

Hydrophobic poly(lactic acid), PLA, was modified to give hydrophilicity and dyeability to cationic dyes via UV/O₃ irradiation. The UV irradiation treatment caused ester linkage of PLA surface to break down resulting in reduced molecular weight and generation of new photooxidized products as indicated in subtracted ATR spectra and ESCA analysis. It was found that water contact angle decreased from 61 ° to 39 ° and surface energy slightly increased with increasing UV energy, which was attributed to significant contribution of polar component rather than nonpolar component resulting from the surface photooxidation of PLA. Also the surface treatment increased dyeability of PLA to C.I. Basic Blue 41 in terms of both K/S and %E. The increased dyeability may be due to photochemically introduced anionic and dipolar dyeing sites which electrostatically interact with the cationic dye as ascertained by the decreased zeta potential and its pH dependence of the modified PLA.     

Properties of modified ethylene terpolymer/poly(lactic acid) blends based films

In order to explore an alternative method instead of plasticization for improving the toughness, flexibility and processability of PLA based packaging films, two different kinds of modified polyethylene based elastomers, such as glycidyl methacrylate or maleic anhydride functionalized ethylene-acrylate based elastomers, were melt blended with PLA. Their properties were compared with conventional PEG plasticized PLA. The chemical interaction between end groups of PLA and epoxide or maleic anhydride functional groups of elastomers was shown by FTIR. Scanning electron microscopy showed that up to 20 % PEG loading, one phase morphology was achieved, however beyond this point, a phase separation was observed for plasticized PLA. For PLA/elastomer blends, a two-phase morphology was obtained as a result of immiscible nature of PLA and elastomers. Tensile and dynamic mechanical properties indicated that elastomer based blends were better than plasticized PLA independently from elastomer type. Differential scanning calorimeter (DSC) analysis exhibited that the T _g value was remarkably lowered in the plasticized PLA; however, it did not change in the case of elastomers. In terms of oxygen permeability and biodegradability, plasticized PLA was found to be better than elastomer based blends.     

Mechanical properties of denim fabric reinforced poly(lactic acid)

Denim, a twilled cotton fabric, was used to enhance the mechanical and thermal properties of poly(lactic acid) (PLA). The denim fabric reinforced composites with different numbers of denim layers were fabricated by using a hand layup method. The impact, tensile, and dynamic mechanical properties of the composites were observed with increasing denim layers to examine the reinforcing effect of denim fabrics. Numerical analysis was carried out to model the elastic modulus of the composite by using a commercial software. Three-dimensional geometry of the denim fabric reinforced PLA composite was generated through a CAD program, and the elastic modulus was calculated by applying uniform deformation on one surface. The impact strength, tensile strength, and thermal properties of the composites were improved by piling denim fabrics. The denim fabric reinforced composites exhibited outstanding impact strength due to the retarded crack propagation as well as large energy dissipation. The 3 layer denim reinforced composite showed best results among all specimens, and its impact strength, tensile strength, and tensile modulus were measured to be 82 J/m, 75.76 MPa, and 4.65 GPa, respectively. The PLA/denim composites have good mechanical properties and can substitute traditional composites such as glass fiber or carbon fiber reinforced composites.     

Thermal and structure properties of biobased cellulose nanowhiskers/poly (lactic acid) nanocomposites

Cellulose nanowhiskers were used to improve the performance of poly (lactic acid) (PLA). The nanocomposites mixed with three different molecular weight of poly (ethylene glycol) (PEG) were characterized by mechanical testing, thermal gravimetry and differential scanning calorimetry. The tensile test showed an increase in tensile strength and elongation at break with the addition of PEG to PLA/CNW nanocomposites, the thermal analysis results showed an increase of crystallization temperature (T _c) and crystallization compatibility (larger crystallization and melting areas), which indicated that the cellulose nanowhiskers (CNW) and PEG or CNW alone should not be considered as nucleating agents for the PLA matrix; The CNW was homo-dispersed which contributed to decreasing mobility of polymer chain segments. The compatibility between hydrophobic PLA matrix and the hydrophilic CNW was improved by the addition of different molecular weight polymeric-PEG. The thermo gravimetric analysis indicated that the thermal stability of the different composites were reflected well in the region between 25 °C and 245 oC. The structure of the PLA/CNW/PEG composites was characterized by AFM, which showed that the CNW dispersed in the PLA matrix evenly.     

Cellulose nanowhisker-incorporated poly(lactic acid) composites for high thermal stability

In this study, biodegradable composites were prepared using cellulose nanowhiskers and poly(lactic acid). For processing at high temperature over 200 °C, cellulose nanowhiskers were prepared by ultra-sound treatment, with the high thermal stability of natural cellulose. The nanowhiskers were confirmed using transmission electron microscopy, X-ray diffraction, and thermo-gravimetric analysis. Surface modification of the cellulose nanowhiskers was performed to increase the adhesion between hydrophilic nanofillers and hydrophobic polymer matrix. The dynamic mechanical thermal analysis of the composites showed better reinforcing effect of the modified cellulose nanocrystals. The effects of cellulose nanowhiskers on the biodegradability of poly(lactic acid) were studied using a microbial oxidative degradation analyzer.     

Soy protein isolate/poly(lactic acid) injection-molded biodegradable blends for slow release of fertilizers

A slow release fertilizer system consisting of materials derived exclusively from biomass, and suitable for i) production of injection-molded parts such as containers for growing plants, and ii) use as granules, is reported. Soy (Glycine max L. Merr.) protein isolate/poly(lactic acid) blends plasticized with triacetin (SPI/PLA-TA) were used as matrix for NPK fertilizer incorporation. Upon melt processing, this composite material formed a highly ordered porous matrix of SPI in which PLA domains are homogeneously dispersed with NPK salts. Dynamic conductivity measurements indicated good release properties as the cumulative amount increased much slower with time as compared to pure NPK sample. Biodegradation was accessed by examining weight loss and surface morphology as a function of incubation time in soil.     

Unique crystallization behavior of multi-walled carbon nanotube filled poly(lactic acid)

Although poly(lactic acid) (PLA) possesses many desirable properties such as miscible, reproducible, nontoxic, and biodegradable properties, extremely slow crystallization rate is a weak point in comparison with other commercial thermoplastics. Addition of nucleating agents can be a good method to increase the overall crystallization rate and multi-walled carbon nanotube (MWCNT) is generally known as a good nucleating agent as well as reinforcement. MWCNT reinforced PLA nanocomposites were prepared by melt blending and the unique nucleation and crystallization behaviors of pure PLA and MWCNT/PLA nanocomposites were investigated. Slow homogeneous nucleation and crystallization behavior of the pure PLA and fast heterogeneous crystallization behavior of MWCNT/PLA nanocomposites were observed. Crystallization behavior of MWCNT/PLA nanocomposites was irrespective of cooling rate and the peculiar behavior was due to fast heterogeneous crystallization caused by the nucleating effect of MWCNT and fast PLA chain mobility.     

Functinalization of poly(ethylene terephthalate) fibers by grafting of maleic acid/methacrylamide monomer mixture

Functionalized poly(ethylene terephthalate) (PET) fibers were synthesized by grafting of maleic acidmethacrylamide (MAA-MAAm) monomer mixtures by using benzoylperoxide as initiator onto PET fibers in an aqueous medium. The functionalized fibers were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimeter, and scanning electron microscopy. The effects of reaction conditions, such as monomer mixture ratio, monomer mixture and initiator concentration, polymerization time, and temperature on grafting were investigated. In alone grafting of MAA, grafting was not observed. However, the use of MAAm as a comonomer increased the amount of MAA inserted to the PET fiber up to 40.7 %. An increase in the temperature between 75 and 95 °C and also, increase in monomer mixture concentration between 0.50 and 1.00 M increased the grafting rate and saturation graft yield. The graft yield has shown an increase up to an initiator concentration of 1.0×10⁻² M and decreased afterwards. The grafting increased the dyeability with disperse, acidic and basic dyes, and water absorption capacity but decreased the thermal stability of the fibers.     

Pervaporation separation of dimethyl carbonate/methanol binary mixtures with poly(vinyl alcohol)-perfluorslulfonic acid/poly(acrylonitrile) hollow fiber composite membranes

Using poly(vinyl alcohol) (PVA) and perfluorslulfonic acid (PFSA) as coating materials, poly(acrylonitrile) (PAN) hollow fiber ultrafiltration membrane as substrate, PVA-PFSA/PAN composite membranes were fabricated by dip-coating method. The fabricated composite membranes were used to the separation of dimethyl carbonate (DMC)/methanol (MeOH) binary mixtures by pervaporation process. SEM images verify that the coated layer is well combined with substrate and the thickness nearly linearly increases with the coating solution concentration. The separation factor increases but at cost of the decline of permeation flux when the concentration of the coating solution or its PVA mass fraction increase. The permeation flux increases and separation factor slightly increases with the feed temperature increasing at 30–60 °C. The increase of feed MeOH concentration leads to an improvement of permeation flux and a decline of separation factor.     

Thermo-mechanical and morphological properties of short natural fiber reinforced poly (lactic acid) biocomposite: Effect of fiber treatment

Untreated oil palm empty fruit bunch (REFB), alkali treated EFB (AEFB), ultrasound treated EFB (UEFB) and simultaneous ultrasound-alkali treated EFB (UAEFB) short fibers were incorporated in poly(lactic acid) (PLA) for fabricating bio-composites. The REFB fiber-PLA (REPC) and treated EFB (TEFB) fiber-PLA (TEPC) composites were prepared and characterized. Glass transition temperature, crystal melting temperature, decomposition temperature, melt flow index, density and mechanical properties (tensile strength, tensile modulus and impact strength) of TEPC are found to be higher than those of REPC. The observed crystallization temperature of TEPC is lower than that of REPC. Among all samples, TEPC prepared from UAEFB fiber shows better performances than other samples fabricated by REFB and AEFB fibers. Scanning electron microscopy, Fourier transform infrared spectroscopy and XRD analyses well support all the observed results.     

The influence of fiber diameter of electrospun poly(lactic acid) on drug delivery

Electrospinning is a simple process for the production of fibers with diameters in the range from submicron to micron. Herein we aim to explore the influence of fibrous diameter on the drug delivery. The feasible methods by making choice of solvents and changing flow rate were used to prepare 5-fluorouracil-loaded polylactide (PLA) fibers with a large diameter gap. The drug release behavior in vitro was investigated and analyzed in phosphate buffer solution. The drug distribution and fiber diameter both affected the initial burst release. The results showed that all the asspun fibers could not avoid of burst release. The coarse fibers exhibited slight burst release as compared to fine fibers. During the second stage, the fine fibers released faster than that of the coarse fibers. For the whole release stage, the large-diameter fibers seemed to be beneficial for drug release in the long term and smoothly. The MTT results showed that the cytotoxicity of drugs was maintained.     

Tensile behavior and structural evolution of poly(lactic acid) monofilaments in glass transition region

A series of amorphous poly(lactic acid) (PLA) monofilaments with various D-isomer contents of 1∼9 mol% have been prepared and then elongated uniaxially at 25∼65 °C in the glass transition region. Both initial modulus and maximum strength of PLA monofilaments are appreciably decreased with increasing the temperature, especially at ∼50 °C, and they were somewhat lower for the monofilament with higher D-isomer content. Structural evolution, chain orientation, and thermal properties of PLA monofilaments drawn uniaxially with various draw ratios at 65 °C were then investigated by using wide-angle X-ray diffraction, polarized Raman spectroscopy, and differential scanning calorimetry, respectively. X-ray diffraction patterns clearly exhibited the development of chain orientation and stain-induced crystallization of the monofilaments as a function of draw ratio (DR). The dichroic ratio, a measure of the chain orientation, was quantitatively evaluated from the polarized Raman spectra. It was revealed that the dichroic ratios increased up to DR=4 and decreased slightly at DR>4 owing to the strain-induced crystallization for PLA monofilaments with D-isomer contents of 1 and 4 mol%. The glass transition and cold-crystallization temperatures of PLA monofilaments increased and decreased, respectively, with the increment of DR. The strain-induced enthalpy relaxation endothermic peak appearing in glass transition region became intense with increasing the DR.     

Preparation and properties of pineapple leaf fiber reinforced poly(lactic acid) green composites

Green composites from Pattawia pineapple leaf fiber (PALF) and poly(lactic acid) (PLA) were prepared. The mechanical method was chosen to extract PALF from fresh leaves due to this method gave high yield of fiber, short extraction time, and environmental friendly. Tensile and thermal properties, together with morphology of the fibers were disclosed. The fibers were conducted into a specified length of 1–3 mm and blended with PLA, using a twin screw extruder, with the PALF content of 10–50 wt%. Tensile testing, morphology investigation and thermogravimetric analysis were applied. Preliminary results showed that tensile modulus of the composites depended on PALF content. The tensile modulus and elongation at break of the composite containing 40 % PALF was about 48 %, and 111 % increase, respectively, compared with that of PLA. With addition of maleic anhydride coupling agent, such the composite showed the tensile modulus of 5.1 GPa, which was 34 % higher than that of the non-coupling agent composite, and about 104 % higher than that of PLA. Although the elongation at break of the composite containing 40 % PALF was found to dramatically increase by 111 %, the introduction of maleic anhydride in such the composite caused only 57 % increase in the elongation at break compared with that of PLA. Finally, a pilot product of square boxes was produced successfully from the proposed composite, by conventional injection molding process.     

Development and characterization of alginate-chitosan-hyaluronic acid (ACH) composite fibers for medical applications

Natural materials and plants have a long history of medical applications due to their broad range of favorable biological functions including biocompatibility, anti-bacterial, anti-oxidant and anti-inflammatory properties. Main objective of this study was to develop alginate-chitosan-hyaluronic acid (ACH) composite fibers with controlled drug release, and liquid retention properties for better moist wound healing. The dope comprising sodium alginate was extruded into calcium chloride (CaC1₂) coagulation bath. The developed calcium alginate fibers were then passed through a bath containing hydrolyzed chitosan and dip coated with hyaluronic acid for 24 hours. The resulting ACH composite fibers were then rinsed with deionized water and dried using acetone. These fibers were tested for tensile properties, % swelling, liquid absorption (g/g) and controlled drug release. The results concluded that ACH composite fibers can be produced by wet spinning and have adequate tensile properties, high % swelling, liquid absorption (g/g) and controlled release of hyaluronic acid for improved wound healing.     

Bio-composites: Development and mechanical characterization of banana/sisal fibre reinforced poly lactic acid (PLA) hybrid composites

The work focuses on the influencing effect of fiber surface treatment by BP towards mechanical properties of BSF reinforced PLA composites. BSF were treated by BP to improve the adhesion between fibres and matrix. BSF (30 wt %) reinforced PLA (70 wt %) hybrid composites were fabricated by means of twin screw extrusion followed by injection molding process. Tensile strength, flexural strength and modulus were tested by means of UTM. The morphological analysis of the untreated and treated BSF reinforced PLA composites in comparison with virgin PLA was carried out by SEM to examine the existence of interfacial adhesion between BSF and PLA. The resultant data reveals that treated BSF restricts the motion of the PLA matrix due to better wettability and bonding. Consequently, mechanical properties like tensile and flexural moduli of BSF reinforced PLA composites were enhanced in comparison to virgin PLA and untreated BSF reinforced PLA composites. The results are discussed in detail.     

Dispersant-free dyeing of poly(lactic acid) knitted fabric with temporarily solubilized azo disperse dyes

Poly(lactic acid) (PLA) is known for environmentally friendly material as it is derived from annually renewable crops and biodegradable. Dispersant-free dyeing of PLA fabric with three temporarily solubilized azo disperse dyes which contain β-sulfatoethylsulfonyl group was investigated and their dyeing and fastness properties were compared with those of commercial disperse dyes. The temporarily solubilized azo disperse dyes were successfully applied to PLA fabric without the use of dispersant. The color yield on PLA fabric was dependent on dyebath pH and dyeing temperature as well. The optimum results were obtained at pH 7-8 and 110 °C. The dyes showed markedly higher color yield on PLA fabric when compared to commercial disperse dyes. Wash fastness was very poor to poor but light fastness was good. The COD levels of the dyeing effluent from the temporarily solubilized disperse dyes were considerably lower than those from commercial disperse dyes.     

Evaluation of cotton byproducts as fillers for poly(lactic acid) and low density polyethylene

Polymeric composites based on cotton burr and cottonseed bull have been prepared by melt blending and extrusion. For poly(lactic acid) (PLA) and low-density polyethylene (LDPE), addition of the fillers slightly changed the composite's thermal properties but significantly decreased the composite's mechanical properties. Heat treatment prior to extrusion resulted in composites with better tensile strength and Young's modulus. The use of maleic anhydride and peroxide only slightly improved the physical properties of the LDPE materials, but the effect was less clear for the PLA materials. The PLA-filler composites may be useful for lowering the cost of the materials in applications that can tolerate the decreased properties. In addition, the addition of fillers to LDPE might be beneficial in applications to improve stiffness or to improve biodegradability.     

Effect of various parameters on the chemical grafting of amide monomers to poly(lactic acid)

Radical melt graft copolymerizations of poly (lactic acid) (PLA) with amide monomers using benzoyl peroxide as an initiator during reactive extrusion is studied. The effects of two monomer types at various concentrations, reaction temperatures and initiator concentrations on the grafting yield are investigated. The results showed that percentage of grafting was significantly enhanced by increasing benzoyl peroxide concentrations up to 12 mpm and then decreased by an increase in the initiator concentration. Furthermore, increasing each monomer concentration up to 450 mpm, improved the grafting yield significantly. Further increase brings about a marked fall in the grafting yield. Fourier Transform Infrared Spectroscopy (FTIR), back titration and nitrogen analyses confirmed that monomers of acrylamide and methacrylamide were successfully grafted onto PLA. The Gel Permeation Chromatography (GPC) data showed that the molecular weight of the grafted PLA samples under optimum conditions does not show any dramatic drop of PLA molecular weight by thermal degradation or hydrolysis of polyester chains, while the polydispersity index is poorly affected by the chemical modification of PLA. Also, the monomer structures affected the grafting yield as well as polymer chain combination. In addition under the same conditions, the grafting yield of acrylamide was more than that of methacrylamide. Thermal properties, molecular weight, density, moisture regain and tensile properties of the samples were also measured.