Production Of Polylactic Acid Research Articles

Anaerobic Codigestion of Food Waste and Polylactic Acid: Effect of Pretreatment on Methane Yield and Solid Reduction

Food waste and biopolymers, plastics derived from plants, are unexploited sources of energy when discarded in landfills without energy recovery. In addition, polylactic acid (PLA) and food waste have complimentary characteristics for anaerobic digestion; both are organic and degrade under anaerobic conditions. Lab-scale reactors were set up to quantify the solubilization of pretreated amorphous and crystalline PLA. Biochemical methane potential (BMP) assays were performed to quantify CH4 production from both treated and untreated PLA in the presence of food waste and anaerobic digested sludge. Amorphous and crystalline PLA reached near-complete solubilization at 97% and 99%, respectively, when alkaline pretreatment was applied. The PLA that received alkaline treatment produced the most of CH4 throughout the run time of 70 days. The PLA without treatment resulted in 54% weight reduction after anaerobic digestion. Results from this study show that alkaline pretreatment has the greatest solid reduction of PLA and maximum production of CH4 when combined with food waste and anaerobic digested sludge.

Steps Toward High-Performance PLA: Economical Production of d-Lactate Enabled by a Newly Isolated Sporolactobacillus terrae Strain.

Optically pure d-lactate production has received much attention for its critical role in high-performance polylactic acid production. However, the current technology can hardly meet the comprehensive demand of industrialization on final titer, productivity, optical purity, and raw material costs. Here, an efficient d-lactate producer strain, Sporolactobacillus terrae (S. terrae) HKM-1, is isolated for d-lactate production. The strain HKM-1 shows extremely high d-lactate fermentative capability by using peanut meal, soybean meal, or corn steep liquor powder as a sole nitrogen source; the final titers (205.7 g L-1 , 218.9 g L-1 , and 193.9 g L-1 , respectively) and productivities (5.56 g L-1 h-1 , 5.34 g L-1 h-1 , and 3.73 g L-1 h-1 , respectively) of d-lactate reached the highest level ever reported. A comparative genomic analysis between S. terrae HKM-1 and previously reported d-lactate high-producing Sporolactobacillus inulinus (S. inulinus) CASD is conducted. The results show that many unrelated genetic features may contribute to the superior performance in d-lactate production of S. terrae HKM-1. This d-lactate producer HKM-1, along with its fermentation process, is promising for sustainable d-lactate production by using agro-industrial wastes.

Exfoliated graphite/acrylic composite film as hydrophobic coating of 3D-printed polylactic acid surfaces

Three-dimensional (3D) printers utilize polylactic acid (PLA) as feedstock filament due to its renewability, low extrusion temperature, and good mechanical properties. One major drawback of 3D-printed PLA products is their limited application in harsh environments due to their low hydrolytic resistance. We developed exfoliated graphite (EG)/acrylic composite films as protective coatings of 3D-printed PLA surfaces. This paper reports on the water contact angles (WCAs) and weight change behavior of 3D-printed PLA surfaces coated with EG/acrylic composite films under humid exposure. We obtained hydrophobic films (WCA > 90°) after adding EG platelets to the acrylic resin. Moreover, the films retain their hydrophobicity after a long humid exposure. The films also reduce the water absorption of 3D-printed PLA surfaces. The addition of stearic acid in the coating formulation further enhances the water resistance of the films. In conclusion, the hydrophobic EG/acrylic composite films improve the hydrolytic resistance of 3D-printed PLA surfaces. The use of EG over defect-free graphene to create hydrophobic polymeric films will need to be considered in future studies.

Recent Advances in d-Lactic Acid Production from Renewable Resources: Case Studies on Agro-Industrial Waste Streams.

SUMMARYThe production of biodegradable polymers as alternatives to petroleum-based plastics has gained significant attention in the past years. To this end, polylactic acid (PLA) constitutes a promising alternative, finding various applications from food packaging to pharmaceuticals. Recent studies have shown that d-lactic acid plays a vital role in the production of heat-resistant PLA. At the same time, the utilization of renewable resources is imperative in order to decrease the production cost. This review aims to provide a synopsis of the current state of the art regarding d-lactic acid production via fermentation, focusing on the exploitation of waste and byproduct streams. An overview of potential downstream separation schemes is also given. Additionally, three case studies are presented and discussed, reporting the obtained results utilizing acid whey, coffee mucilage and hydrolysate from rice husks as alternative feedstocks for d-lactic acid production.

Use of Candida rugosa lipase as a biocatalyst for L-lactide ring-opening polymerization and polylactic acid production

Abstract Candida rugosa lipase (CRL, EC Number: 232–619-9) is a stable enzyme, and its use is relatively widespread in the field of biotechnology, especially in hydrolysis reactions, esterification, transesterification and enantioselective biotransformation. This study examined the role of CRL as a biocatalyst for L-lactide ring-opening polymerization in the production of metal-free polylactic acid (PLA). The ring-opening polymerization reaction was conducted at various temperatures (70, 90, 110 and 130 °C) and CRL concentrations (1, 2, 3 (%w/w)). The results revealed a strong relationship between PLA formation and CRL activity. The highest CRL activity was obtained in ring-opening polymerization of L-lactide at a temperature of 90 °C and concentration of 2% (w/w). Under these conditions, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of PLA analyzed by gel permeation chromatography was highest at 5428 and 2854 g/mol respectively, with a yield of 93% and the enzyme activity 0.39 U. The polymerization of lactide at 90 °C occurred only in the presence of the catalyst. The crystallinity and melting point of PLA were 31% and 120 °C, respectively. Scanning electron microscopy (SEM) analysis of the morphology of PLA revealed smooth and uniform pores in each region, with mass percentage of the elements carbon (C) and oxygen (O) of 52% and 48%, respectively.

Metabolic Engineered Biocatalyst: A Solution for PLA Based Problems.

Polylactic acid (PLA) is a biodegradable thermoplastic polyester. In 2010, PLA became the second highest consumed bioplastic in the world due to its wide application. Conventionally, PLA is produced by direct condensation of lactic acid monomer and ring opening polymerization of lactide, resulting in lower molecular weight and lesser strength of polymer. Furthermore, conventional methods of PLA production require a catalyst which makes it inappropriate for biomedical applications. Newer method utilizes metabolic engineering of microorganism for direct production of PLA through fermentation which produces good quality and high molecular weight and yield as compared to conventional methods. PLA is used as decomposing packaging material, sheet casting, medical implants in the form of screw, plate, and rod pin, etc. The main focus of the review is to highlight the synthesis of PLA by various polymerization methods that mainly include metabolic engineering fermentation as well as salient biomedical applications of PLA.

Systematic assessment of triticale‐based biorefinery strategies: sustainability assessment using multi‐criteria decision‐making (MCDM)

AbstractTriticale – a hybrid of rye and wheat – is a man‐made crop that has the potential to be a preferred feedstock for the biorefinery in Canada because of its ability to grow on marginal land, its high yields, and its non‐competition with food‐based crops. However, it is challenging to identify sustainable investment options among the many possible triticale‐based biorefinery pathways. Several product‐process combinations for the production of polylactic acid (PLA) were defined in this study, each involving different degrees of technology and market risk. The different biorefinery configurations had conflicting rankings considering different criteria, making a trade‐off analysis essential to assess the most sustainable biorefinery strategies. Economic, competitive, and environmental dimensions of the biorefinery alternatives were thus evaluated in a multi‐criteria decision‐making (MCDM) panel, so that the triticale‐based biorefinery strategies could be ranked using a sustainability perspective.In this study, a set of ten criteria determined as the most important through previously‐conducted MCDMs were presented to a decision‐making panel. They determined that for PLA production, maximizing electricity production through a straw‐dedicated CHP unit was the least sustainable investment option, due to poor economic and competitiveness performance associated with its capital‐intensiveness and its failure to include a value‐added product portfolio. Therefore, this investment option was screened out from the list of strategies to be further analyzed. On the other hand, options featuring higher technology risk including energy‐efficient separation processes (ultra‐filtration) and integrated fermentation processes (SSCF) attained significantly better sustainability scores due mainly to their low energy and raw materials consumption values. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd

Increasing Profits in Food Waste Biorefinery—A Techno-Economic Analysis

The present manuscript highlights the economic profit increase when combining organic waste anaerobic digestion with other mixed culture anaerobic fermentation technologies, e.g., lactic acid fermentation and dark fermentation. Here we consider the conversion of 50 tonnes/day of food waste into methane, power generation (from CHP of biomethane), lactic acid, polylactic acid, hydrogen, acetic acid and butyric acid. The economic assessment shows that the basic alternative, i.e., anaerobic digestion with methane selling to the grid, generates 19 USD/t_VS (3 USD/t_foodwaste) of profit. The highest profit is obtained by dark fermentation with separation and purification of acetic and butyric acids, i.e., 296 USD/t_VS (47 USD/t_foodwaste). The only alternative that presented losses is the power generation alternative, needing tipping fees and/or subsidy of 176 USD/t_VS (29 USD/t_foodwaste). The rest of the alternatives generate profit. From the return on investment (ROI) and payback time, the best scenario is the production of polylactic acid, with 98% ROI, and 7.8 years payback time. Production of butyric acid ROI and payback time was 74% and 9.1 years.

Effects of process parameters on the quality of PLA products fabricated by fused deposition modeling (FDM): surface roughness and tensile strength

Abstract This study investigates the effects of process parameters on the quality of products fabricated by fused deposition modeling (FDM), such as surface roughness and tensile strength. Polylactic acid (PLA) samples were built on a FDM machine at various layer thicknesses, nozzle temperature and deposition head velocity. The effect of cooling the samples during the process was also considered. The experimental study was performed according to a mixed type Taguchi L16 orthogonal array. The effectiveness of each parameter was also discussed by an analysis of variance (ANOVA). The tensile strength results were compatible with the optical images of the fracture surfaces while the surface roughness results were compatible with the surface topography of the parts along the thickness. The two dominant quality characteristics were found to be layer thickness and deposition head velocity. Lower layer thickness values yielded higher tensile strength and lower surface roughness. Use of a cooling fan and nozzle temperature were found to be the least effective parameters. Finally, the results indicated that tensile strength and surface quality of the FDM samples improved about 25 %, and 12 %, respectively at optimal process conditions.

Production of Lactic Acid from Empty Fruit Bunch of Palm Oil Using Catalyst of Barium Hydroxide

Lactic Acid as a platform chemical has broad application in various industries, especially in the production of Poly Lactic Acid (PLA) for biodegradable plastic. Empty fruit bunch (EFB), abundant by product from palm oil mill industry, is one of potential feedstock to be used in the production of lactic acid from lignocellulose biomass. EFB contains high cellulose and hemicellulose about 37– 59.7% w/w and 16–28% w/w, respectively. The aim of this paper is to study the effects of the operating conditions, such as temperature, reaction time, biomass loading, and catalyst concentration on the yield of lactic acid using barium hydroxide as alkaline catalyst. EFB pretreatment with steam explosion was applied to remove lignin content. The results showed that pretreatment reduced the lignin content from 22.66% to 9.69% w/w. Meanwhile, hemicellulose and cellulose increased from 14.40% to 16.40% w/w and 29.37% to 63.57% w/w, respectively. The highest yield of lactic acid was 21.57% C-mol, achieved by using 0.25 M Ba(OH)2 as the catalyst, with 5% w/v biomass loading, temperature 240°C, during 4 h reaction times. The yield was approximately equal to yield of lactic acid (~ 20%) compared with Pb2+ as the catalyst for EFB conversion although the later catalyst produced fewer by products during conversion.

Bacillus coagulans MA-13: a promising thermophilic and cellulolytic strain for the production of lactic acid from lignocellulosic hydrolysate

BackgroundThe transition from a petroleum-based economy towards more sustainable bioprocesses for the production of fuels and chemicals (circular economy) is necessary to alleviate the impact of anthropic activities on the global ecosystem. Lignocellulosic biomass-derived sugars are suitable alternative feedstocks that can be fermented or biochemically converted to value-added products. An example is lactic acid, which is an essential chemical for the production of polylactic acid, a biodegradable bioplastic. However, lactic acid is still mainly produced by Lactobacillus species via fermentation of starch-containing materials, the use of which competes with the supply of food and feed.ResultsA thermophilic and cellulolytic lactic acid producer was isolated from bean processing waste and was identified as a new strain of Bacillus coagulans, named MA-13. This bacterium fermented lignocellulose-derived sugars to lactic acid at 55 °C and pH 5.5. Moreover, it was found to be a robust strain able to tolerate high concentrations of hydrolysate obtained from wheat straw pre-treated by acid-catalysed (pre-)hydrolysis and steam explosion, especially when cultivated in controlled bioreactor conditions. Indeed, unlike what was observed in microscale cultivations (complete growth inhibition at hydrolysate concentrations above 50%), B. coagulans MA-13 was able to grow and ferment in 95% hydrolysate-containing bioreactor fermentations. This bacterium was also found to secrete soluble thermophilic cellulases, which could be produced at low temperature (37 °C), still retaining an optimal operational activity at 50 °C.ConclusionsThe above-mentioned features make B. coagulans MA-13 an appealing starting point for future development of a consolidated bioprocess for production of lactic acid from lignocellulosic biomass, after further strain development by genetic and evolutionary engineering. Its optimal temperature and pH of growth match with the operational conditions of fungal enzymes hitherto employed for the depolymerisation of lignocellulosic biomasses to fermentable sugars. Moreover, the robustness of B. coagulans MA-13 is a desirable trait, given the presence of microbial growth inhibitors in the pre-treated biomass hydrolysate.

Valorization of Agri-Food Waste via Fermentation: Production of l-lactic Acid as a Building Block for the Synthesis of Biopolymers

Global interest towards lactic acid production has recently significantly increased because lactic acid can be used as raw material for the production of polylactic acid (PLA), a polymer used in biodegradable plastics for its special, environmentally-friendly properties. However, the high production costs have hindered the large-scale application of PLA due to the high price of lactic acid. Here we evaluated the potential of pear pomace and ricotta cheese whey (RCW) as a low-cost source of nutrients for lactic acid fermentation of Lactobacillus casei and Lactobacillus farciminis in microaerophilic conditions and mild sterility. After an initial lab-scale screening of 19 lactic acid bacteria (LAB) strains to select the highest producer of lactic acid, we reported the 1L-batch scale-up to test process efficiency and productivity of the most promising LAB strains. Batch fermentation of a 25:75 mixture of pear pomace and RCW, respectively, reached an overall yield factor of 90% and a volumetric productivity of 0.42 g/L·h.

PREPARATION AND CHARACTERIZATION OF PLASTICIZED POLYLACTIC ACID/STARCH BLEND

Petroleum based packaging materials has raised environmental concerns due to its non-environmentally friendly degradation. Conventional plastic takes a long time to degrade and remains in the waste dump. Since then, attention to biodegradable plastics has been heightened for its greener degradation. Polylactic acid (PLA) is a renewable polymer with mechanical properties comparable to those of the conventional plastics. This study aims to improve the mechanical and thermal properties and reducing the cost of PLA production by blending PLA with starch as filler and epoxy palm oil (EPO) as plasticizer. The PLA/starch/EPO blends were prepared by solution casting and melt blending methods and properties of the blends were studied and characterized. The thermal properties of plasticized PLA/starch were investigated by Differential Screening Calorimetry (DSC) followed by Fourier Transform Infra-Red Spectroscopy (FT-IR) in order to observe the degree of interaction of plasticized PLA/starch blend. The mechanical properties were investigated using Universal Tensile Test

Technological aspects of the production of biodegradable polymers and other chemicals from renewable sources using lactic acid

Lactic acid produced from renewable sources is used for the production of polylactic acid and lactic acid-based biodegradable polymers. However, large-scale production of biodegradable polymers and other large-tonnage lactic acid-based chemical products is limited by the difficulties of production-related waste and low productivity. To overcome these problems, we developed a method of ammonium lactate production from carbohydrates using a membrane bioreactor and semicontinuous cultivation with controlled parameters. During the 130 cycles, the average specific productivity of the biochemical reactor for ammonium lactate was 56 g L−1·h−1, which was 10-fold higher than that obtained using traditional industrial processes. This method of using concentrated biomass in membrane reactors may also be applied in other similar processes of microbial transformation of organic substances. To significantly reduce the waste produced in the form of calcium sulfate, lactic acid derivatives were isolated from the butyl lactate intermediate without calcium sulfate formation. A method for the production of large-volume chemicals such as propylene glycol was also developed through hydrogenation of butyl lactate on a copper oxide–silica catalyst. This highly effective process gave 99% yield and 99% selectivity for propylene glycol formation. Our data on the development and improvement of the production processes of lactic acid and its derivatives pave the way for the development of competitive industrial processes for the production of biodegradable polymers and large-tonnage chemical products based on renewable raw materials.

Improved lactic acid productivity by simultaneous recovery during fermentation using resin exchanger

Lactic acid is a versatile organic acid that can be used in various applications. One of the promising applications of lactic acid is in bioplastic industry. Lactic acid is used as the monomer building block in polylactic acid synthesis. Unlike the existing applications in food and pharmaceutical industries in which lactic acid is used as the additive, it becomes the major raw material in polylactic acid production. This, therefore, raises the demand of lactic acid and eventually increases the market price. In order to expedite the bioplastic industry, cost competitiveness to the existing plastic is a big concern. The cost effectiveness and process robustness are the key success factors in bioplastic industry. Currently, lactic acid is produced via bacterial fermentation using the lime-based process. After fermentation, lactic acid was recovered from the fermentation broth by various techniques including solvent extraction, reactive distillation, ion exchanger, and electrodialysis. To achieve low production cost, not only high fermentation rate is necessary, effective recovery process is also required. In this study, we attempted simultaneous recovery of lactic acid coupled with fermentation to drive the productivity and long-term operation in continuous culture. Anion exchange resin, Amberlite IRA-400, was selected for recovering lactic acid from the bacterial culture. The preliminary results in batch adsorption showed that among other resins studied, Amberlite IRA-400 provided the best separation efficiency. Further study on fixed bed adsorption and simultaneous fermentation and lactic acid recovery using this resin were conducted and the results will be discussed in this presentation.

ChemInform Abstract: Lactide Synthesis and Chirality Control for Polylactic Acid Production

AbstractReview: [67 refs.

Biochemical and Structural Insights into Enzymatic Depolymerization of Polylactic Acid and Other Polyesters by Microbial Carboxylesterases.

Polylactic acid (PLA) is a biodegradable polyester derived from renewable resources, which is a leading candidate for the replacement of traditional petroleum-based polymers. Since the global production of PLA is quickly growing, there is an urgent need for the development of efficient recycling technologies, which will produce lactic acid instead of CO2 as the final product. After screening 90 purified microbial α/β-hydrolases, we identified hydrolytic activity against emulsified PLA in two uncharacterized proteins, ABO2449 from Alcanivorax borkumensis and RPA1511 from Rhodopseudomonas palustris. Both enzymes were also active against emulsified polycaprolactone and other polyesters as well as against soluble α-naphthyl and p-nitrophenyl monoesters. In addition, both ABO2449 and RPA1511 catalyzed complete or extensive hydrolysis of solid PLA with the production of lactic acid monomers, dimers, and larger oligomers as products. The crystal structure of RPA1511 was determined at 2.2 Å resolution and revealed a classical α/β-hydrolase fold with a wide-open active site containing a molecule of polyethylene glycol bound near the catalytic triad Ser114-His270-Asp242. Site-directed mutagenesis of both proteins demonstrated that the catalytic triad residues are important for the hydrolysis of both monoester and polyester substrates. We also identified several residues in RPA1511 (Gln172, Leu212, Met215, Trp218, and Leu220) and ABO2449 (Phe38 and Leu152), which were not essential for activity against soluble monoesters but were found to be critical for the hydrolysis of PLA. Our results indicate that microbial carboxyl esterases can efficiently hydrolyze various polyesters making them attractive biocatalysts for plastics depolymerization and recycling.

Lactide Synthesis and Chirality Control for Polylactic acid Production.

Polylactic acid (PLA) is a very promising biodegradable, renewable, and biocompatible polymer. Aside from its production, its application field is also increasing, with use not only in commodity applications but also as durables and in biomedicine. In the current PLA production scheme, the most expensive part is not the polymerization itself but obtaining the building blocks lactic acid (LA) and lactide, the actual cyclic monomer for polymerization. Although the synthesis of LA and the polymerization have been studied systematically, reports of lactide synthesis are scarce. Most lactide synthesis methods are described in patent literature, and current energy-intensive, aselective industrial processes are based on archaic scientific literature. This Review, therefore, highlights new methods with a technical comparison and description of the different approaches. Water-removal methodologies are compared, as this is a crucial factor in PLA production. Apart from the synthesis of lactide, this Review also emphasizes the use of chemically produced racemic lactic acid (esters) as a starting point in the PLA production scheme. Stereochemically tailored PLA can be produced according to such a strategy, giving access to various polymer properties.

Life-Cycle Assumptions of Landfilled Polylactic Acid Underpredict Methane Generation

The life-cycle assessment (LCA) tool, Waste Reduction Model, currently applies no methane generation to landfilled polylactic acid (PLA), considering the carbon sequestered. A selection of PLA products were analyzed by the biochemical methane potential (BMP) assay, and the results were compared to LCA model values. BMPs were performed at 35 and 55 °C on a variety of single-use products that would be disposed alongside food scraps. No biodegradation was observed for any product after incubation at 35 °C for 60 days. PLA products generated 185–372 mL of CH4/g of volatile solids at 55 °C after 60 days, some approaching the theoretical methane potential. The results here indicate that PLA may generate significant quantities of methane in an anaerobic landfill environment, which can reach thermophilic temperatures, and the current assumption of PLA as an absolute carbon sink in landfills is incorrect.

From Laboratory to Industrial Continuous Production of Polylactic Acid with Low Residual Monomer

SummaryPolylactic acid (PLA) is a 100 % bio‐based polyester with strong market growth potential in commodity applications as a substitute of fossil‐based polymers such as PET, PE and PS. The successful commercialization of this material relies on the possibility to devolatilize efficiently the unreacted monomer, which, in turn, requires an effective quenching of the polymerization catalyst. In this contribution we report an experimental screening of potential catalyst deactivators performed in small scale batch reactions. The best performing deactivator was then tested on a continuous PLA production plant of 1 kta to prove the reliability of the experimental approach. The plant data confirmed that the use of the selected deactivator improves the efficiency of the devolatilization process and leads to PLA with superior optical properties.