Laboratory composting of extruded starch acetate and poly lactic acid blended foams

Composting of extruded foams made of starch acetate and poly lactic acid (PLA) with pre-conditioned yard waste was studied using a laboratory composting system. Extruded foams of high amylose starch were used as the control. Degradation was measured by analyzing the exhaust gases for carbon dioxide. There were significant differences in the amounts of carbon dioxide produced in the vessels containing foams of high amylose starch and foams of starch acetate blended with 20% or 30% PLA. The high amylose starch foams completely degraded within 15 days. The starch acetate foams with 0% PLA took longer, with evolution of carbon dioxide still measurable after 55 days. The rate of degradation was faster for foams with higher PLA contents. The starch acetate foams took even longer to degrade. The maximum time was found to be 130 days for the starch acetate foams.     

Technological and economic potential of poly(lactic acid) and lactic acid derivatives

Abstract: Lactic acid has been an intermediate-volume specialty chemical (world production ∼ 40,000 tons/yr) used in a wide range of food processing and industrial applications. Lactic acid has the potential of becoming a very large volume, commodity-chemical intermediate produced from renewable carbohydrates for use as feedstocks for biodegradable polymers, oxygenated chemicals, plant growth regulators, environmentally friendly 'green' solvents, and specialty chemical intermediates. The recent announcements of new development-scale plants for producing lactic acid and polymer intermediates by major U.S. companies, such as Cargill, Ecochem (DuPont/ConAgra), and Archer Daniels Midland, attest to this potential.
In the past, efficient and economical technologies for the recovery and purification of lactic acid from crude fermentation broths and the conversion of lactic acid to the chemical or polymer intermediates had been the key technology impediments and main process cost centers. The development and deployment of novel separations technologies, such as electrodialysis (ED) with bipolar membranes, extractive distillations integrated with fermentation, and chemical conversion, can enable low-cost production with continuous processes in large-scale operations. The use of bipolar ED can virtually eliminate the salt or gypsum waste produced in the current lactic acid processes. Thus, the emerging technologies can use environmentally sound processes to produce environmentally useful products from lactic acid. The process economics of some of these processes and products can also be quite attractive. In this paper, the recent technical advances in lactic and polyactic acid processes are discussed. The economic potential and manufacturing cost estimates of several products and process options are presented. The technical accomplishments at Argonne National Laboratory (ANL) and the future directions of this program at ANL are discussed.     

Electrospinning of poly(lactic acid) stereocomplex nanofibers

The electrospinning of stereocomplex nanofibers of high-molecular-weight poly(L-lactic acid) (PLLA)/poly(D-lactic acid) (PDLA) (PLLA/PDLA = 1:1) was carried out with chloroform as the spinning solvent. The stereocomplex nanofibers with diameters of 830-1400 and 400-970 nm were successfully obtained at voltages of -12 and -25 kV, respectively. Wide-angle X-ray scattering indicated that with an increasing absolute value of voltage from 0 to 25 kV the crystallinity of homo-crystallites composed of either PLLA or PDLA decreased from 5% to 1%, whereas the crystallinity of stereocomplex crystallites increased slightly from 16% to 20%. The obtained results reveal that electrospinning is an effective method to prepare stereocomplex nanofibers with a negligibly small amount of homo-crystallites, even when high-molecular-weight PLLA and PDLA are used, and that the orientation caused by high voltage (or electrically induced high shearing force) during electrospinning enhances the formation and growth of stereocomplex crystallites and suppresses the formation of homo-crystallites.     

From lactic acid to poly(lactic acid) (PLA): characterization and analysis of PLA and its precursors

The quality of the monomers lactic acid and lactide as well as the chemical changes induced during polymerization and processing are crucial parameters for controlling the properties of the resulting poly(lactic acid) (PLA) products. This review presents the most important analysis and characterization methods for quality assessment of PLA and its precursors. The impurities typically present in lactic acid or lactide monomers and their possible origins and effects on resulting PLA products are discussed. The significance of the analyses for the different polymer production stages is considered, and special applications of the methods for studying features specific for PLA-based materials are highlighted.     

Preparation of biocompatible chitosan grafted poly(lactic acid) nanoparticles

Chitosan grafted poly(lactic acid) (CS-g-PLA) copolymer was synthesized and characterized by FT-IR and elemental analysis. The degree of poly(lactic acid) substitution on chitosan was 1.90 ± 0.04%. The critical aggregation concentration of CS-g-PLA in distilled water was 0.17 mg/ml. Three methods of preparing CS-g-PLA nanoparticles (diafiltration method, ultrasonication method and diafiltration combined with ultrasonication method) were investigated and their effect was compared. Of the three methods, diafiltration combined with ultrasonication method produced nanoparticles with optimal property in terms of size and morphology, with size ranging from 133 to 352 nm and zeta potential from 36 to 43 mV. Also, the hemolytic activity and cytotoxicity of the CS-g-PLA based nanoparticles was tested, and results showed low hemolysis rate (<5%) and no significant cytotoxicity effect of these nanoparticles.     

Stereocomplex formation between enantiomeric poly(lactic acid)s. 12. spherulite growth of low-molecular-weight poly(lactic acid)s from the melt

The spherulite growth of stereocomplex crystallites in the blend from low-molecular-weight poly(L-lactide) [i.e., poly(L-lactic acid) (PLLA)] and poly(D-lactide) [i.e., poly(D-lactic acid) (PDLA)] from the melt, together with that of the homocrystallites in pure PLLA and PDLA films, was investigated using polarization optical miscroscopy. The spherulite growth of stereocomplex crystallites occurred at a wider temperature range (相似文献   

Preparation and properties of plasticized poly(lactic acid) films

Poly(lactic acid), PLA, was blended with monomeric and oligomeric plasticizers in order to enhance its flexibility and thereby overcome its inherent problem of brittleness. Differential scanning calorimetry, dynamic mechanical analysis, transmission electron microscopy, and tensile testing were used to investigate the properties of the blends. Monomeric plasticizers, such as tributyl citrate, TbC, and diethyl bishydroxymethyl malonate, DBM, drastically decreased the T(g) of PLA, but the blends showed no morphological stability over time since rapid cold crystallization caused a size reduction of the amorphous domains in PLA. Consequently, the ability of PLA to accommodate the plasticizer diminished with the increase in crystallinity and migration of the plasticizer occurred. Increasing the molecular weight of the plasticizers by synthesizing oligoesters and oligoesteramides resulted in blends that displayed T(g) depressions slightly smaller than with the monomeric plasticizers. The compatibility with PLA was dependent on the molecular weight of the oligomers and on the presence or not of polar amide groups that were able to positively interact with the PLA chains. Aging the materials at ambient temperature revealed that the enhanced flexibility as well as the morphological stability of the films plasticized with the oligomers could be maintained as a result of the higher molecular weight and the polar interactions with PLA.     

Metalloinitiation routes to biocompatible poly(lactic acid) and poly(acrylic acid) stars with luminescent ruthenium tris(bipyridine) cores

Poly(lactic acid) (PLA) and poly(acrylic acid) (PAA) biomaterials with luminescent ruthenium tris(bipyridine) centers couple drug delivery and imaging functions. Hydrophobic [Ru(bpyPLA2)3](PF6)2 (1) was generated from [Ru[bpy(CH2OH)2]3](PF6)2 in bulk monomer using 4-(dimethylamino)pyridine as the catalyst. The bromoesters, [Ru[bpy(CH2OR)2]3](PF6)2, [Ru[bpy(C13H27)2][bpy(CH2OR]2](PF6)2 (4), and [Ru[bpy(PLAOR)2]3]2+ (9) (R=COCBr(CH3)2), served as initiators for tert-butyl acrylate (tBA) polymerization. Conversion of PtBA to PAA via hydrolysis affords water soluble materials, [Ru(bpyPAA2)3]2+ (7) and [Ru[bpy(C13H27)2](bpyPAA2)2]2+ (8) and the amphiphilic star polymer [Ru[bpy(PLA-PAA)2]3)](PF6)2 (11), which is soluble in a H2O/CH3CN (1:1) mixture. Luminescence excitation and emission spectra of the Ru polymers were in agreement with the parent [Ru(bpy)3]2+ chromophore (lambdaex=468, lambdaem=621 nm). Lifetimes of tau approximately 700 ns in both air and nitrogen atmospheres are typical for most materials; however, the amphiphilic star block copolymer 11 is quenched by oxygen to some degree. Thermal analysis shows the expected glass transitions for the polymeric ruthenium complex materials.     

聚乳酸成核剂研究进展

聚乳酸是以乳酸为原料而合成得到的一种高分子材料,具有良好生物相容性、可生物降解性。目前工业规模化生产的聚乳酸主要是以左旋乳酸合成得到的聚乳酸,制得的制品透明性好,但缺点是不能耐热。添加成核剂可以提高聚乳酸的结晶度,从而提高它的耐热性能。本文综述了有机成核剂和无机成核剂的研究进展。     

乳丝的加工、性能及其应用

乳丝学名为聚乳酸纤维,是一种可生物降解的新型绿色纤维,目前制备方法主要有熔融纺丝、溶液纺丝和静电纺丝等3种方法。作为一种新型的可降解纤维材料,其环保性、吸湿性、透气性、生物相容性以及优良的力学性能决定了其在生物医用、织物面料、非织造材料(如一次性卫生用品、过滤材料等)等很多方面都将得到广泛应用。     

Extractive lactic acid fermentation in poly (ethyleneimine)-based aqueous two-phase system

The potential of an aqueous two-phase system composed of a polycation, poly(ethyleneimine) (PEI), and an uncharged polymer, (hydroxyethyl) cellulose (HEC), for extractive lactic acid fermentation was tested. Batch fermentation with 20 g/L glucose in two-phase medium using Lactococcus lactis without external pH control resulted in 3-4 times higher amount of lactate and biomass produced as compared to that in a conventional one-phase medium. Lactic acid was preferentially partitioned to the PEI-rich bottom phase. However, the cells which favored the HEC-rich top phase in a fresh two-phase medium were partitioned to a significant extent to the bottom phase after fermentation. Addition of phosphate buffer or pH adjustment to 6.5 after fermentation caused fewer cells to move to the bottom phase. With external pH control, fermentation in normal and two-phase medium showed no marked differences in glucose consumption and lactic acid yield, except that about 1.3 times higher cell density was obtained in the two-phase broth, especially at initial glucose concentrations of 50-100 g/L. Use of higher concentration of phosphate during batch fermentation in the two-phase medium with 50 g/L sugar provided a 15% higher yield of lactic acid, but the growth rate of cells was nearly half of the normal, thus affecting the productivity. Continuous fermentation with twice the normal phosphate concentration resulted in higher cell density, product yield, and productivity in two-phase medium than in monophasic medium. (c) 1996 John Wiley & Sons, Inc.     

Solid state microcellular foamed poly(lactic acid): morphology and property characterization

Poly(lactic acid) or PLA is a plant-based biodegrable plastic which exhibits many properties that are equivalent to or better than many petroleum-based plastics. However, there have been few commercial applications due to its lower impact resistance and higher cost than synthetic plastics. In this paper, the concept of creating microcellular foamed structures in PLA as a means to improve its shortcomings is presented. The effect of the foaming conditions (temperature and time) on the void fraction, volume expansion ratio, impact strength and tensile properties of foamed PLA is discussed. Each step of microcellular processing is addressed including: the manufacture of PLA film; the saturation of the samples with gas; the microcellular foaming of PLA; the void fraction determination, volume expansion ratio calculation, impact and tensile property characterization of foamed samples. The microcellular morphologies developed in PLA samples were a strong function of the foaming conditions. Due to the presence of foamed microcells, a twofold expansion ratio and significant improvements in the impact resistance (twofold increase over unfoamed PLA), strain at break (up to twofold increase over unfoamed PLA) and toughness (up to fourfold increase over unfoamed PLA) were achieved in PLA.     

Cell morphology of extrusion foamed poly(lactic acid) using endothermic chemical foaming agent

Poly(lactic acid) (PLA) was foamed with an endothermic chemical foaming agent (CFA) through an extrusion process. The effects of polymer melt flow index, CFA content, and processing speed on the cellular structures, void fraction, and cell-population density of foamed PLA were investigated. The apparent melt viscosity of PLA was measured to understand the effect of melt index on the cell morphology of foamed PLA samples. The void fraction was strongly dependent on the PLA melt index. It increased with increasing melt index, reaching a maximum value, after which it decreased. Melt index showed no significant effect on the cell-population density of foamed samples within the narrow range studied. A gas containment limit was observed in PLA foamed with CFA. Both the void fraction and cell-population density increased with an initial increase in CFA content, reached a maximum value, and then decreased as CFA content continued to increase. The processing speed also affected the morphology of PLA foams. The void fraction reached a maximum value as the extruder’s screw speed increased to 40 rpm and a further increase in the processing speed tended to reduce the void fraction of foamed samples. By contrast, cell-population density increased one order of magnitude by increasing the screw speed from 20 to 120 rpm. The experimental results indicate that a homogeneous and finer cellular morphology could be successfully achieved in PLA foamed in an extrusion process with a proper combination of polymer melt flow index, CFA content, and processing speed.     

Development of nitrogen-removal bioreactor using poly(lactic acid) as an energy source.

To control nitrogen such as ammonia in a rearing water of aquatic animals, we developed new bioreactor capable of both nitrification and denitrification. It was consisted of gel-plate immobilized microorganisms and a biodegradable plastic plate composed of three kind of poly(lactic acid) as an energy source of denitrification. When batch treatment experiment by the bioreactor was continuously carried out with an artificial rearing water containing ammonia, nitrogen-removal rate of the bioreactor was approximately 3 g-N/d/m2-gel surface and the activity was maintained for over 3 month without additional energy source. Therefore, the bioreactor would be effective to control nitrogen concentration in rearing water of a closed water circulating system for aquatic animals.     

Laboratory evaluation of lactic acid on attraction of Culex spp. (Diptera: Culicidae)

The role of lactic acid was evaluated for attraction of Culex nigripalpus, Culex quinquefasciatus, Culex tarsalis, and Aedes aegypti in the laboratory using a dual‐port olfactometer. When lactic acid was combined with chicken odor, attraction was increased for Cx. quinquefasciatus compared to chicken odor alone but not for Cx. nigripalpus, Cx. tarsalis, and Ae. aegypti. Lactic acid combined with hand odor did not change attraction of Cx. tarsalis and Ae. aegypti but decreased attraction of Cx. nigripalpus and Cx. quinquefasciatus. The addition of lactic acid to CO₂ increased attraction of Ae. aegypti and Cx. quinquefasciatus but reduced attraction of Cx. nigripalpus and Cx. tarsalis. Use of commercial lactic acid baits with CO₂ resulted in a similar trend except for Cx. nigripalpus which showed no difference. A blend of lactic acid, acetone, and dimethyl disulfide was attractive to Ae. aegypti (63.4%) but elicited low responses by all Culex spp. (1.3–26.8%). Addition of the blend to CO₂ increased attraction of Ae. aegypti and Cx. quinquefasciatus but reduced attraction of Cx. nigripalpus and Cx. tarsalis. The mixture of compounds plus CO₂ was as attractive as a hand for Cx. quinquefasciatus, Cx. tarsalis, and Ae. aegypti.     

Compatible ternary blends of chitosan/poly(vinyl alcohol)/poly(lactic acid) produced by oil-in-water emulsion processing

Ternary compatible blends of chitosan, poly(vinyl alcohol), and poly(lactic acid) were prepared by an oil-in-water (O/W) emulsion process. Solutions of chitosan in aqueous acetic acid, poly(vinyl alcohol) (PVA) in water, and poly(lactic acid) (PLA) in chloroform were blended with a high-shear mixer. PVA was used as an emulsifier to stabilize the emulsion and to reduce the interfacial tension between the solid polymers in the blends produced. It proved to work very well because the emulsions were stable for periods of days or weeks and compatible blends were obtained when PVA was added. This effect was attributed to a synergistic effect of PVA and chitosan because the binary blends PVA/PLA and chitosan/PLA were completely incompatible. The blends were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), stress-strain tests, and Fourier transform infrared spectroscopy (FTIR). The results indicated that despite the fact that the system contained distinct phases some degree of molecular miscibility occurred when the three components were present in the blend.     

Stereocomplex formation by enantiomeric poly(lactic acid) graft-type phospholipid polymers for tissue engineering

A porous scaffold as a cell-compatible material was designed and prepared using a phospholipid copolymer composed of 2-methacryloyloxyethyl phosphorylcholine (MPC), n-butyl methacrylate, and enantiomeric macromonomers, the poly(L-lactic acid) (PLLA) macromonomer, and poly(D-lactic acid) (PDLA) macromonomer. On the basis of the wide-angle X-ray diffraction and differential scanning calorimetry measurements, the formation of a stereocomplex between the PLLA and PDLA segments of the copolymer was observed on the porous scaffold. The porous structure was prepared by a sodium chloride leaching technique, and the pore was linked to the scaffold. The pore size was confirmed by scanning electron microscopy and found to be ca. 200 microm. These observations suggest that the porous scaffold makes it possible to produce cell-compatible materials, which may involve the following advantages for tissue engineering: (i) cell compatibility using phospholipid copolymer, (ii) adequate cell adhesion by poly(lactic acid), and (iii) complete disappearance of scaffold by dissociation of stereocomplex. The cell experiment using the porous scaffold will be the next subject and reported in a forthcoming paper.     

Tacticity control in the synthesis of poly(lactic acid) polymer stars with dipentaerythritol cores

The synthesis of a family of polymer stars with arms of varied tacticities is discussed. The effect of polymer tacticity on the physical properties of these polymer stars is presented. Dipentaerythritol cores support six poly(lactic acid) (PLA) arms. Lewis acidic tin and aluminum catalysts control the polymerization to afford polymer stars of variable tacticity. The analysis of these polymers by NMR spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and differential scanning calorimetry reveals the effects of tacticity control on the physical properties of the polymer stars. Preliminary decomposition studies suggest that the biodegradation profile of a polymer star may also be tuned by stereochemical control. This is the first systematic altering of tacticity in PLA polymer stars, showing that polymer tacticity can have a great impact on star properties.     

Cellular behavior of neointima-like cells onto vitamin E-enriched poly(D,L)lactic acid

In-stent restenosis is a process that occurs in 10-50% of cases currently treated with stent and it is caused by an abnormal smooth muscle cell (SMC) proliferation and migration in the vascular lumen. One of the most promising strategy to reduce restenosis is stent coating with biodegradable polymers to deliver in situ anti-proliferative drugs. Poly(D,L)lactic acid (P(D,L)LA), one of the most interesting candidate for stent coating, has been observed to induce inflammation and neointimal proliferation. In our laboratory, we developed P(D,L)LA enriched with Vitamin E (Vit.E), an anti-oxidative and anti-inflammatory agent that reduces also SMC proliferation. In order to evaluate the in vitro cellular behaviour of neointima cells onto Vitamin E-enriched P(D,L)LA, cell adhesion and proliferation along with the expression of two SMC migration markers (MMP-9 and hyaluronic acid receptor CD44) were measured in rat vascular SMC A10 cells seeded onto control P(D,L)LA (PLA) and P(D,L)LA films containing 10-30% (w/w) Vit.E (PLA10-30). Cell adhesion, proliferation and MMP-9 production were unaffected by the Vit.E presence in the PLA films after 24 h, while proliferation was slowed or blocked after 48 and 72 h onto PLA10, 20 and 30. MMP-9 production was almost blocked and CD44 density decreased significantly after 72 h for cells grew onto PLA30 compare to cells seeded onto PLA. These data indicate that Vit.E-enriched P(D,L)LA could be an interesting polymer for stent coating.     

Molecular recognition by Kluyveromyces of amphotericin B-loaded, galactose-tagged, poly (lactic acid) microspheres

In an effort to develop a new way of drug delivery, especially for polyenic antifungal molecules, we have incorporated amphotericin B (AmB) into biodegradable galactosylated poly (L-lactic acid) (L-PLA) and poly (L-lactic-co-glycolic acid) (PLGA) microspheres. These drug carriers were prepared by solvent evaporation using an oil/water (o/w) emulsion. The ratio of galactosyl spacers with different chain lengths was 1.74-2.78%. The maximal quantity of AmB encapsulated reported to 100 mg of the galactosylated microspheres was 7.14 mg for L-PLA (encapsulation rate 45% of mole) and 6.42 mg for PLGA derivatives (encapsulation rate 81% of mole). In our yeast model, drug release depended on three factors: (i) presence of galactosylated antennae, (ii) length of galactosyl antenna and (iii) nature of the polymer. More of the AmB trapped in PLGA microspheres was released than from PLA microspheres. These novel functionalised microspheres could be required for the delivering of therapeutic agents according to their recognition to specific cells.