• Macromolecular Research
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• v.10 no.6
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• pp.359-364
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• 2002

A series of PLA-PEO-PLA triblock stereo-copolymers with varying PLA/PEO and L-DL-LA ratios were synthesized via ring opening pelymerizations. Aqueous solutions of these copolymers undergo thermo-responsive phase transitions as the temperature monotonically increases. Further study shows that there is a critical gel concentration (CGC), and also lower and upper critical gel temperatures (CGTs), at which the thermo-responsive phase transition occurs. The CGC and CGTs are affected by various factors such as block length, as well as the compositions of the PLA blocks and of the additives. In particular, the changes in the phase diagram produced by varying the L-/DL-LA ratio in the PLA blocks were determined to be mainly due to consequent stereo-regularity changes in the PLA blocks.

• Macromolecular Research
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• v.14 no.5
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• pp.510-516
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• 2006

Lactide was produced from oligomeric PLA by back-biting reaction of the OH end groups. For optimization of the reaction conditions, the effects of temperature, pressure, PLA molecular weight, and catalyst type on the lactide synthesis were examined. The fraction of D,L-lactide decreased with increasing temperature. Among the various Sn-based catalysts, the D,L-lactide fraction was maximized when SnO was used. A higher yield with lower racemization was observed at lower pressure. The conversion of PLA was maximized at an oligomeric PLA molecular weight of ca. 1380. The yield of lactide increased but the fraction of D,L-lactide decreased with increasing molecular weight. The highest conversion with the lowest racemization degree was obtained at a catalyst concentration of 0.1 wt%. The lactide was more sensitive to racemization because of the entropic effect.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.44 no.6
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• pp.28-35
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• 2012

Water-in-oil emulsion (W/O) and oil-in-water emulsion (O/W) types biodegradable polymer emulsions prepared to PLA and PBS. The optimal mixing ratio of polymer : solvent : OA : TEA : water was found be 10 : 40 : 4 : 6 : 30(g) when preparing emulsions. Biodegradability was most retained after preparation of polymer emulsions. Particle size of PLA and PBS emulsions were 2-3 ${\mu}m$ and 3-4 ${\mu}m$, respectively. Molecular weight of PLA and PBS emulsions were 108,000 and 92,000, respectively. And molecular weight of PLA and PBS emulsions became slightly lower than those of pellets.

• Applied Chemistry for Engineering
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• v.24 no.1
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• pp.104-111
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• 2013

Poymer blends of two degradable aliphatic polyesters, relatively expensive material polylactic acid (PLA) and relatively inexpensive material poly(butylene adipate-co-terephthalate) (PBAT), were used in this study. Three different kinds of modifiers were used with various amounts. Diisocyanate type methylenediphenyl 4,4'-diisocyanate (MDI) and hexamethylene diisocyanate (HDI) were used as modifiers and epoxy type coupling agents also used. The melt flow index (MFI) and dynamic viscoelasticity of various compositions of PLA/PBAT blends were studied. The mechanical property and morphology with respect to the fracture surface of PLA/PBAT blends were also investigated using tensile test and field emission scanning electronic microscopy, respectively. These tests were also used to verify the compatibility of PLA/PBAT and the effect of mechanical properties due to the use of modifiers. Tensile properties of PLA/PBAT blends modified with HDI were improved remarkably.

• Macromolecular Research
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• v.10 no.3
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• pp.158-167
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• 2002

In order to endow with new bioactive functionality from small intestine submucosa (SIS) powder as natural source to poly (L-lactide) (PLA) and poly (lactide-co-glycolide) (PLGA) synthetic biodegradable polymer, porous SIS/PLA and SIS/PLGA as natural/synthetic composite scaffolds were prepared by means of the solvent casting/salt leaching methods for the possibility of the application of tissue engineered bone and cartilage. A uniform distribution of good interconnected pores from the surface to core region was observed the pore size of 40~500 ${\mu}{\textrm}{m}$ independent with SIS amount using the solvent casting/salt leaching method. Porosities, specific pore areas as well as pore size distribution also were almost same. After the fabrication of SIS/PLA hybrid scaffolds, the wetting properties was greatly enhanced resulting in more uniform cell seeding and distribution. Five groups as PGA non-woven mesh without glutaraldehyde (GA) treatment, PLA scaffold without or with GA treatment, and SIS/PLA (Code No.3 ; 1 : 12 of salt content, (0.4 : 1 of SIS content, and 144 ${\mu}{\textrm}{m}$ of median pore size) without or with GA treatment were implanted into the back of nude mouse to observe the effect of SIS on the induction of cells proliferation by hematoxylin and eosin, and von Kossa staining for 8 weeks. It was observed that the effect of SIS/PLA scaffolds with GA treatment on bone induction are stronger than PLA scaffolds, that is to say, in the order of PLA/SIS scaffolds with GA treatment > PLA/SIS scaffolds without GA treatment > PGA nonwoven > PLA scaffolds only with GA treatment = PLA scaffolds only without GA treatment for the osteoinduction activity. The possible explanations are (1) many kinds of secreted, circulating, and extracellular matrix-bound growth factors from SIS to significantly affect critical processes of tissue development and differentiation, (2) the exposure of SIS to GA resulted in significantly calcification, and (3) peri-implant fibrosis due to covalent bonding between collagen molecule by crosslinking reaction. In conclusion, it seems that SIS plays an important role for bone induction in SIS/PLA scaffolds for the application of tissue engineering area.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.42 no.2
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• pp.75-81
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• 2010

Characteristics of mixing biodegradable polymers and polymer impregnated paper for mulching mat for seedling were investigated. The mixed film of 70% PLA was most easily biodegradable. The surface of polymer films were changed to more rough due to enzymatic degradation of lipase. Tensile strength and breaking elongation of PLA mixed films were increased to the 0.04-0.31 kN/m and the 0.17-0.96%, respectively. With higher PLA contents, intensities of ester originated carboxyl group(about $1,748cm^{-1}$) were increased. Physical properties of prepared mulching mats were increased with PLA contents and stiffness of mulching mat was not so much changed.

• Polymer(Korea)
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• v.36 no.6
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• pp.745-755
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• 2012

Two types of polymers were tested in this study; poly(ethylene terephthalate) (PET) as a synthetic example and poly(lactic acid) (PLA) as a natural polymer. DSC analyses showed that the use of nanofiller increased the degree of crystallinity ($X_c$) of both PET and PLA polymers, but the effect was more noticeable on PET nanocomposites. The crystallization of PLA and PET nanocomposites occurred at higher temperatures in comparison to neat polymers. According to dynamic mechanical-thermal analysis (DMTA), the damping factor of PET/$TiO_2$ nanoparticles decreased compared to the neat matrix, but for PLA nanocomposites the opposite trend was observed. Results of the mechanical test showed that for both PET and PLA nanocomposites, the most successful toughening effect was observed at 3 wt% loading of $TiO_2$ nanoparticles. SEM micrographs revealed uniform distribution of $TiO_2$ nanoparticles at 1 and 3 wt% loading levels. The results of WAXD spectra explained that the polymorphs of PLA and PET was not affected by $TiO_2$ nanoparticles. UV-visible spectra showed that $TiO_2$ nanocomposite films had high ultraviolet shielding compared to neat polymer, but there was significant reduction in transparency.

• Biomaterials and Biomechanics in Bioengineering
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• v.1 no.2
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• pp.95-104
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• 2014

The objective of this study was to evaluate the cytotoxicity of poly (lactic acid) (PLA) nanoparticles. We used a water-soluble, amphiphilic phospholipid polymer, poly (2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) (PMB30W), as a stabilizer for the PLA nanoparticles. The PLA nanoparticles and PMB30W-modified PLA (PLA/PMB30W) nanoparticles were prepared by evaporating tetrahydrofuran (THF) from its aqueous solution. Precipitation of the polymers from the aqueous solution produced PLA and PLA/PMB30W nanoparticles with a size distribution of $0.4-0.5{\mu}m$. The partial coverage of PMB30W on the surface of the PLA/PMB30W nanoparticles was confirmed by X-ray photoelectron spectroscopy (XPS) and dynamic light-scattering (DLS). A high-content automated screening assay (240 random fields per group) revealed that the PLA nanoparticles induced apoptosis in a mouse macrophage-like cell line (apoptotic population: 73.9% in 0.8 mg PLA/mL), while the PLA/PMB30W nanoparticles remained relatively non-hazardous in vitro (apoptotic population: 13.8% in 0.8 mg PLA/mL). The reduction of the apoptotic population was attributed to the phosphorylcholine groups in the PMB30W bound to the surface of the nanoparticle. In conclusion, precipitation of PLA in THF aqueous solution enabled the preparation of PLA nanoparticles with similar shapes and size distribution but different surface characteristics. PMB30W was an effective stabilizer and surface modifier, which reduced the cytotoxicity of PLA nanoparticles by enabling their avoidance of the mononuclear phagocyte system.

• Elastomers and Composites
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• v.50 no.1
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• pp.62-67
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• 2015

The surface modification of microfibriled cellulose (MFC) was carried out through the hydrolysis-condensation reaction using (3-aminopropyl)triethoxysilane (APS) and 3-glycidyloxypropyltriethoxysilane (GPS) and then the modified cellulose was compounded with bio-degradable poly(lactic acid) (PLA). Also, pristine MFC was compounded with PLA as a control groups. The confirmation of surface modification for the pristine MFC was characterized by FT-IR and SEM/EDX. The thermal and mechanical properties of the PLA/MFC composites depended on the content of MFC and the type of silane coupling agents. From the thermal, morphological and mechanical behaviors of the PLA/MFC composites, it was found that GPS-MFC was more successful to improve the interface adhesion between PLA matrix and the surface of MFC than that of APS-MFC.

• Textile Coloration and Finishing
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• v.34 no.3
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• pp.197-206
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• 2022

The purpose of this study was to confirm the optimal spinning conditions for PLA (Polylactic acid) as a fiber forming polymer. According to the melt spinning test results of PLA, the optimal spinning temperature was 258℃. However, it needs to note that relatively high pack pressure was required for spinning at 258℃. At an elevated temperature, 262℃, mono filament was broken easily due to hydrolysis of PLA at a higher temperature. In case of fiber strength, it was confirmed that the draw ratios of 2.7 to 3.3 were optimal for maximum strength of melt spun PLA. Above the draw ratio, 3.3, the strength of the PLA fibers was lowered. It was presumed that cleavage of the PLA polymer chain over maximum elongation. The heat setting temperature of GR (Godet roller) showed that the maximum strength of the PLA fibers was revealed around 100℃. The degree of crystallinity and the strength of the PLA fibers were decreased above 100℃. The optimal take-up speed (Spinning speed) was around 4,000m/min. Thermal analysis of PLA showed 170℃ and 57℃ as Tm (melting temperature) and Tg (glass transition temperature), respectively.