Novel Glycopolymers Based on d-Mannose and Methacrylates: Synthesis, Thermal Stability and Biodegradability Testing

This paper presents the synthesis, thermal stability and biodegradability of new d-mannose glycopolymers. These glycopolymers have been obtained by free radical bulk copolymerization of d-mannose based glycomonomer, 1-O-(2′-hydroxy-3′-methacryloyloxypropyl)-2,3:5,6-di-O-isopropylidene-d-mannofuranose (Mm), and respectively d-mannose derived oligomer (Mo) with methyl methacrylate and respectively 2-hydroxypropyl methacrylate. The chemical structures of Mm and Mo have been confirmed via FTIR, ¹H-NMR and HPLC–MS spectroscopy. The copolymerization process has been investigated using differential scanning calorimetry, which allowed calculating the activation energies by applying Kissinger–Akahira–Sunose method. The glycopolymers are thermally stable, fact assessed by TG analysis; their glass transition temperature exceeds 50 °C, so they are part of the glassy class of polymers. The biodegradability of these glycopolymers has been investigated in vitro, using pure cultures of Zymomonas mobilis and Trichoderma reesei. The glycopolymers lose up to 55 % weight in just 14 days of incubation as their surface and composition is altered by colonies of microorganisms that grow on/into them, fact demonstrated using SEM/EDX.     

Optimization of Microwave-Assisted and Conventional Heating Comparative Synthesis of Poly(lactic acid) by Direct Melt Polycondensation from Agroindustrial Banana (Musa AAA Cavendish) and Pineapple (Ananas comosus) Fermented Wastes

In Costa Rica, a lot of pineapple (Ananas comosus) and banana (Musa AAA) agroindustrial residues are generated each year. These residues can be used to obtain l-lactic acid by fermentation, ultrafiltration and electrodialysis. Poly(l-lactic acid) (PLLA) is a biodegradable and renewable polyester with many industrial and biomedical applications. There is a growing interest to improve the energetic efficiency of the synthesis of PLLA, because the main issue to produce this polymer is the high productive cost compared with petrochemical traditional commodities. In this research, the synthesis of PLLA through two different techniques was compared: microwave-assisted and conventional heating. On microwave synthesis the best results were obtained using lower temperatures and lower reaction times than the conventional heated synthesis. The reaction time was reduced from 15 h by conventional heating to 4.5 h using microwave-assisted synthesis.     

Production of Poly(l-Lactide)-Degrading Enzyme by Amycolatopsis orientalis ssp. orientalis and Its Catalytic Ability in Biological Recycling of Poly(l-Lactide)

The fermentation conditions for poly(l-lactide) (PLA)-degrading enzyme production by Amycolatopsis orientalis ssp. orientalis were statistically optimized by response surface methodology. The optimal value of the most important factors was 0.39 % PLA and 0.34 % gelatin for 2.81 days of cultivation. Under these conditions, the model predicted a PLA-degrading activity of 155.30 U/l. The verification showed the production amount of 154.2 U/l. The crude enzyme from A. orientalis ssp. orientalis showed potent PLA-degrading ability, which is efficient for the biological recycling of PLA. Up to 4,000 mg/l of PLA granule was completely degraded within 5 days at 45 °C by the crude enzyme. l-lactic acid (600 mg/l) was obtained as a degradation product of PLA after only 2 h of incubation. The results indicated that the crude PLA-degrading enzyme from A. orientalis ssp. orientalis has the potential to degrade PLA to lactic acid for the recycling of PLA industry and waste disposal.     

Investigation of pH-Sensitive Swelling and Curcumin Release Behavior of Chitglc Hydrogel

Hydrogels are in use for encapsulation of curcumin for possible use in wound healing. Encapsulation helps in targeted delivery and enhanced activity of curcumin. We report here a pH sensitive hydrogel developed from chitosan. The hydrogel was prepared by reaction of chitosan and d-glucose, facilitated by the reducing agent Na-cyanoborohydride. The maximum yield of the hydrogel was obtained at pH 4.5 with the amount of chitosan, d-glucose and Na-cyanoborohydride as 0.3, 2.0 and 2.0 g respectively. A maximum curcumin loading efficiency of 74% was observed with curcumin amount in the feed at 0.15 g. The release study revealed a sustained release pattern over a period of 80 h with an initial burst release. Curcumin loaded hydrogel showed mild antibacterial activity against Proteus mirabilis and Enterobacter aerogenes.     

Hydrolytic Degradation of PPDO/PDLLA Blends Containing the Compatibilizer PLADO

The poly(para-dioxanone) (PPDO)/poly poly (dl-lactide) (PDLLA) blends containing various contents of compatibilizer (0, 1, 3, 5, 10 %) were prepared by solution co-precipitation, which were dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) to form 10 % wt/vol solutions. Then in vitro hydrolytic degradation of PPDO/PDLLA blends containing poly (dl-lactide-co-para-dioxanone) (PLADO) as the compatibilizer was studied by the changes of weight loss, water absorption, thermal properties, surface morphology and mechanical properties of samples in phosphate buffered saline (pH 7.44) at 37 °C for 8 weeks. During the degradation, the weight loss and water absorption increased significantly for all blends, whereas hydrolysis rate of blends varied with the blend composition. The samples’ glass transition temperature decreased notably, while the degrees of crystallinity increased. Compared with uncompatibilized PPDO/PDLLA blends, PPDO/PDLLA blends with compatibilizer exhibited higher hydrolysis rate. The results suggested that the compatibilizer (PLADO) accelerated the hydrolysis rate of PPDO/PDLLA blends during the degradation.     

Effects of washing with water on enzymatic saccharification and d-lactic acid production from steam-exploded sugarcane bagasse

This study investigated the production of d-lactic acid from unutilized sugarcane bagasse using steam explosion pretreatment. The optimal steam pressure for a steaming time of 5?min was determined. The steam-exploded sugarcane bagasse was hydrolyzed using cellulase (Meicelase) and then the hydrolyzate was subjected to fermentation substrate. By enzymatic saccharification using Meicelase, the highest recovery of glucose from raw bagasse, 73.7?%, was obtained at a steam pressure of 20?atm. For extracted residue with water after steam explosion, the glucose recovery increased up to 94.9?% at a steam pressure of 20?atm. These results showed that washing with water is effective in removing enzymatic reaction inhibitors. After steam pretreatment (steam pressure of 20?atm), d-lactic acid was produced by Lactobacillus delbrueckii NBRC 3534 from the enzymatic hydrolyzate of steam-exploded bagasse and washed residue. The conversion rate of d-lactic acid obtained from the glucose concentration was 66.6?% for the hydrolyzate of steam-exploded bagasse without washing with water and 90.0?% for that derived from the extracted residue with water after steam explosion. These results also demonstrated that the hydrolyzate of steam-exploded bagasse (without washing with water) contains fermentation inhibitors and washing with water can remove them.     

Poly(Lactic Acid)-co-Aspartic Acid Copolymers: Possible Utilization in Drug Delivery Systems

The synthesis and characterization of poly(lactic acid)-co-aspartic acid copolymers (PLA-co-Asp) were presented. Subsequently, the synthesized PLA-co-Asp copolymers were tested as biodegradable carriers in drug delivery systems. PLA-co-Asp copolymers were synthesized by solution polycondensation procedure, using different molar ratios PLA/l-aspartic acid (2.33/1, 1/1, 1/2.33), manganese acetate and phosphoric acid as catalysts and N,N′-dimethyl formamide (DMF)/toluene as solvent mixture. The copolymers were characterized by FT-IR and ¹H-NMR spectroscopy, gel permeation chromatography (GPC), DSC and TG-DTG analyses. Diclofenac sodium, a non steroidal anti-inflammatory drug was subsequently loaded into PLA-co-Asp copolymers. The in vitro drug release experiments were done by dialysis of the copolymer/drug systems, in phosphate buffer solution (pH = 7.4, at 37 °C) and monitored by UV spectroscopy.     

Synthesis and Properties of Poly(d,l-lactide-co-p-dioxanone) Random and Segmented Copolymers

Two different polymerization routes, one-step and two-step bulk ring-opening polymerizations of d,l-lactide (LA) and p-dioxanone (PDO) monermers using stannous octoate [Sn(Oct)₂]/n-dodecanol as the initiating system, were employed to synthesize poly(d,l-lactide-co-p-dioxanone) P(LA-co-PDO) random and segmented copolymers with different compositions and chain microstructure. For the two-step copolymers, the average sequence lengths of the lactidyl (L_LA) and dioxanyl (L_PDO) units calculated from the ¹H-NMR spectra were much longer than those values for the one-step copolymers with the same LA/PDO feed ratio. Corresponding to this difference in microstructure, the two-step copolymers were semi-crystalline even when the PDO content was as low as 14.5 mol%, while the one-step copolymers were completely amorphous with PDO content below 60.6 mol%. However, irrespective of polymerization route, both types of copolymers displayed a single glass transition temperature that was in a linear relation with composition. The decrease of maximum decomposition temperature of the copolymers was in accordance with the decrease of L_PDO value. The mechanical and degradation properties of the copolymers were significantly affected by both the polymerization route and the chemical composition as well. In conclusion, the properties of P(LA-co-PDO) copolymers could be adjusted conveniently to meet specific applications by changing the composition and microstructure of the copolymers via different polymerization routes.     

Production of 2-Pyrrolidone from Biobased Glutamate by Using Escherichia coli

We have developed a simple and highly efficient process for the production of 2-pyrrolidone (2-PRN) from biobased l-glutamic acid (Glu). First, we produced γ-aminobutyric acid (GABA) from Glu obtained by fermentation of biomass using Escherichia coli, which is known to possess GABA producing activity. The reaction solution contained only the substrate Glu, bacterial cells, and water, and did not require buffers or coenzymes, pyridoxal-5′-phosphate (PLP). Every 24 h, cells were removed by centrifugation, and GABA containing supernatant was obtained. This reaction can be repeated 14 times by adding water and Glu, without any decrease in activity. Finally, 303.7 g of GABA was produced from 560 g (40 g × 14 times) of Glu with a yield of 77.4 %. The concentration of this solution was almost 40 %. The GABA was then converted to biobased 2-PRN by heating and distillation under reduced pressure without pretreatment. The yield obtained with this chemical process was 95.8 %. These results showed that biobased 2-PRN could be produced from biomass-derived Glu. Biobased 2-PRN has great potential as a raw material to change other petroleum-based materials to biobased materials.     

Green Synthesis of Silver Nanoparticles and Study of Their Antimicrobial Properties

One of the major disadvantages of polymers when used in food-contact applications is that they are very susceptible to microbial attack. On the other hand, silver nanoparticles have received increased attention as novel antimicrobial agents. Therefore, the introduction of silver nanoparticles into conventional polymers results in new materials with improved properties. In this investigation, colloidal silver nanoparticles using an environmentally friendly procedure were synthesized. An aqueous solution of AgNO₃ was used as a silver precursor with ‘green’ reducing agents either different types of honey, or β-d-glucose. In the first case, different pH values, as well as the addition of poly(ethylene glycol), PEG were studied, while in the latter, the effect of reduction time in the presence of PEG with various average molecular weights was examined. Properties of the nanoparticles were measured using X-Ray diffraction, UV–Vis and FTIR spectroscopy. Using honey it seems that spherical particles are produced with the smaller average particle size obtained at pH 8.5. Use of honey has the advantage of being a natural product, although its main drawback is that its composition varies and it cannot be predefined to result in reproducible results. Use of β-d-glucose results in stable silver nanoparticles with small average particle size after 24 h reduction. The addition of low molecular weight PEG seems to be beneficial in the production of stable nanoparticles. Finally, the antimicrobial activity of the nanoparticles produced was investigated at different concentrations on both Gram positive and negative bacteria, such as Bacillus cereus, Bacillus subtilis, Escherichia coli and Staphylococcus aureus.     

The influence of air inflow on CH4 composition ratio in landfill gas

When landfill gas is collected, air inflow into the landfill can reduce CH₄ productivity. The decline of CH₄ content in landfill gas (LFG) negatively affects energy projects. We studied air inflow rates and LFG characteristics from 699 vertical collection facilities (VCFs) in the 2nd landfill at the Sudokwon Landfill in South Korea. We first determined whether or not N₂ was an effective indicator of air inflow at this site using argon assays. The results of this analysis showed that the denitrification processes could be disregarded and that N₂ was an effective indicator of air inflow. Using the composition of N₂ in LFG samples, we found that air inflow occurred at 73.6 % of the VCFs, and 25.6 % of samples from these facilities showed more than 80 vol% of air inflow. In addition, we observed that the O₂ consumption rate was more than 70 % of the volume in all samples. $ R_{{{\text{CH}}_{ 4} }} $ , which is the ratio of CH₄ to the sum of CH₄ and CO₂, decreased with increasing air inflow. Finally, we found that, as air inflow increased, the variation in $ R_{{{\text{CH}}_{ 4} }} $ values for samples with equal air inflow ratios also increased due to differences in air inflow routes.     

Effect of Nucleation of Tricalcium Phosphate and Isothermal Annealing on the Crystallization of Poly(l-lactide-co-glycolide)

We investigated the effect of nucleation and isothermal annealing on the crystallization behavior of a random copolymer, poly(l-lactide-co-glycolide) (PLLGA), with monomer molar ratios of 85/15 (PLLGA85/15) by scanning electron microscopy, polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction, and examination of the tensile properties of the resultant product. The effect of heterogeneous nucleation was assessed by the addition of tricalcium phosphate (TCP) as a nucleating agent. Nucleation and isothermal annealing of PLLGA at 130 °C were conducted to improve the degree of crystallinity of the copolymer. The fracture surfaces of the TCP/PLLGA85/15 composite bar showed a considerable number of spherulites with TCP as their nucleus. Addition of TCP and subsequent annealing improved the degree of crystallinity. After annealing, the TCP/PLLGA85/15 composite samples gained nearly the same strength that the pure PLLGA85/15 samples possessed. It is believed that this method will enhance the practical application of this nucleating agent in the processing of polymers.     

Microwave Assisted Short-Time Alkaline Extraction of Birch Xylan

Efficacy of microwave energy for the extraction of xylan from birch wood as an alternative to conventional method of extraction was investigated. Effect of irradiation time and microwave power input on the solubilization of wood and yield of extracted xylan was studied. The maximum yield of xylan obtained at the higher power level was significantly lesser compared to the lower power level indicating the molecular degradation of the polymer. The highest yield of xylan (60 % of the original xylan) was obtained at the lowest power level studied, 110 W, for an irradiation time of 10 min. Comparison with conventional extraction showed that 10 min of microwave extraction provided a similar wood dissolution to that at 90 °C for 1.5 h, but with a higher yield of xylan. Characterization of the precipitated xylan indicated that the extracted xylan contained 68–88 % of xylose with the major chemical structure consisting of a linear backbone of (1-4) β-d-xylopyransoyl residues. Molecular mass of the extracted xylan indicated that the xylan extracted using microwave contained 60–70 % of high molecular weight fraction, and about 30–40 % of low molecular weight fraction, whereas xylan extracted using conventional method showed a reverse trend. Molecular mass of non-aggregated xylan was reported to be 6,000 Da (in terms of dextran equivalents). Crystallinity of wood fibers increased irrespective of the method of extraction indicating no degradation of the strength of the fibers occurred during the extraction.     

Dynamic studies on lead volatilization from CaO–SiO2–Al2O3 molten slag under N2–CO–CO2, N2–HCl and N2–H2S gas atmospheres

Dynamic studies on the volatilization of lead from CaO–SiO₂–Al₂O₃ molten slags were conducted in a lab-scale melting furnace from 1623 to 1773 K under different mixed gas atmospheres of CO 0.05–0.3 atm to CO₂ 0–0.3 atm to N₂ (balance), HCl 1.7 × 10^?3–6.7 × 10^?3 atm to N₂ (balance), and H₂S 3.0 × 10^?4 to 1.7 × 10^?3 atm to N₂ (balance). The slag samples consisted of the mixed powders of 20–50 wt% CaO, 30–60 wt% SiO₂, and 10–40 wt% Al₂O₃, containing 2000 ppm PbO.Results showed that the rates of volatilization of lead from the CaO–SiO₂–Al₂O₃ molten slags under the N₂–CO–CO₂, N₂–HCl, and N₂–H₂S gas atmospheres were higher than those under the simulated air (N₂–O₂), which increased with CO, HCl, and H₂S partial pressures. At \(p_{{HCl}}\)  =  \(p_{H_{2}S}\)  = 1.7 × 10^?3 atm, the apparent rate constants for the volatilization of lead under the N₂–H₂S and N₂–HCl gas atmospheres were nearly equal, which increased with a rise in temperature. Results also showed that the rate of volatilization of lead from the molten slag decreased drastically with the increasing viscosity of the molten slag, in the viscosity range lower than 3 Pa s. Consequently, the volatilization of lead from the CaO–SiO₂–Al₂O₃ molten slag was significantly influenced by CO, HCl, and H₂S partial pressures and by the viscosity of the molten slag.     

Non-sterile simultaneous saccharification and fermentation of corn leaves and stalks to <Emphasis Type="SmallCaps">l</Emphasis>-lactic acid without external nutrient addition

Fermentation of lignocellulosic biomass requires auxiliary materials, including nutrients, to ensure the proliferation of microorganisms. Nutrients are usually inexpensive, but their contribution to the cost is considerable because of the very low prices of fermentation products, such as bio-ethanol. Using substances present in native lignocellulosic biomass as nutrients for fermentation was proposed and demonstrated. Leaves and stalks of corn plants were used as biomass, and nutrients were recovered as a nutrient solution by soaking them in water before alkaline peroxide pretreatment. Pretreated biomass and the nutrient solution derived from the same lot were used for non-sterile simultaneous enzymatic saccharification and thermophilic l-lactic acid fermentation (SSF). Using the nutrient solution in the saccharification step did not impact sugar recovery, and instead improved sugar yields because of the presence of eluted sugars in the solution. The l-lactic acid yield of 0.33 g g^?1 based on native biomass weight indicated that the nutrient solution functioned as a source of nutrients and sugars, especially as a source of essential phosphorus. Comparatively, autoclaved SSF yielded less or no l-lactic acid, indicating an apparent inhibitive effect derived from the nutrient solution on bacterial growth.     

Application of ameliorated wood pulp to recover Cd(II), Pb(II), and Ni(II) from e-waste

In this study, dl-malic acid and hydrogen peroxide were used as leaching agents to remove metals from e-waste (printed-circuit boards) and itaconic acid-grafted poly(vinyl alcohol)-encapsulated wood pulp (IA-g-PVA-en-WP) to uptake metals from leachate with high proficiency [11.63 mg g^?1; 93.03 % for Cd(II), 11.90 mg g^?1; 95.18 % for Pb(II), and 12.14 mg g^?1; 97.08 % for Ni(II)]. Metals were recovered from the loaded biosorbent by desorption studies. The standard analytical techniques, such as elemental analysis, Fourier-transform-infrared spectroscopy, scanning electron microscopy, atomic force microscopy, and thermogravimetric analysis, were used to characterize the recovering agent (biosorbent). At equilibrium, the metal uptake data were fitted to Langmuir and D–R isotherms (R ² > 0.99) significantly, revealing, the homogeneous distribution of active sites on biosorbent’s backbone. The possible mechanism appeared to be ion exchanges of metal ions with H⁺ together with binding over functionalities (COO^?). Dimensionless equilibrium parameter (R _L) showed the favourability of metal uptake at lower concentration, while mean adsorption energy (E) certified the physical binding of metal on functionalities which was further confirmed by sticking probability and activation energy parameters. Reusability studies were also conducted to state the performance of biosorbent.     

Crystallization Behavior and Dynamic Mechanical Properties of Poly(l-Lactic Acid) with Poly(Ethylene Glycol) Terminated by Benzoate

Effect of the addition of poly(ethylene glycol) terminated by benzoate (PEG-BA) on the crystallization behavior and dynamic mechanical properties of poly(l-lactic acid) PLLA is studied as compared with poly(ethylene glycol) (PEG-OH). It is found that PEG-BA is miscible with PLLA and shows good plasticizing effect. Because PEG-OH having the same degree of polymerization is immiscible with PLLA, the end group in PEG-BA, i.e., benzoate, plays an important role in the miscibility. Furthermore, PEG-BA does not induce the PLLA degradation at melt-processing, whereas PEG-OH leads to the hydrolysis degradation. Finally, the addition of PEG-BA pronounces the crystallization rate of PLLA at low crystallization temperatures and thus enhances the degree of crystallinity at conventional processing. Consequently, the temperature dependence of dynamic mechanical properties are similar to that for isotactic polypropylene.     

Characterization of dried sewage sludge for co-firing in coal power plant by using thermal gravimetric analysis

This research studied the characteristics of dried sewage sludge using TGA to co-fire dried sewage sludge with coal in power plants. The sewage sludges that were discharged from Daejeon, Korea were dried and examined fundamental properties to use them as a fuel. Also, the properties of bituminous coal and wood pellet, which are used in domestic coal power plants, were analyzed and compared with them of sewage sludges and non-isothermal analyses of dried sewage sludges were performed at the heating rates of 5, 10, 20, and 30C /min using TG analyzer to investigate the basic combustion characteristics. As a results of these TGA/DTG analyses, sewage sludges showed its primary peak at the temperature of 250–500?°C, which overlapped with main peak of wood and secondary peak at around 500–600?°C, which overlapped with main peak of coals. Also for the interpretation by Friedman method, the activation energies in the section of highest weight loss were 525.16 kJ/mole for dried digested sewage sludge, 544.88 kJ/mole for dried excess sewage sludge, 203.86 kJ/mole for wood pellet and 146.4585 kJ/mole for bituminous coal. The reaction orders for dried digested excess sewage sludge, dried excess sewage sludge, wood pellet and bituminous coal were 28.775, 24.319, 18.398 and 9.1005, respectively, and the frequency factors were 5.89?\(\times \hspace{0.17em}\)10²⁸, 1.65?\(\times \hspace{0.17em}\)10^24,, 9.59?\(\times \hspace{0.17em}\)10¹⁶ and 1.77?\(\times \hspace{0.17em}\)10⁸ for each, respectively.     

Comparison of three ornamental plants for phytoextraction potential of chromium removal from tannery sludge

Based on pre-experimentation, three ornamental plants, Mirabilis jalapa, Impatiens Balsamin (I. Balsamin) and Tagetes erecta L., were selected as target plants to study the phytoextraction of chromium (Cr) in tannery sludge irrigated with four treatments according to Cr concentration gradient [Control (CK); 20.50 × 10³ mg kg^?1 (T1); 51.25 × 10³ mg kg^?1 (T2); 102.50 × 10³ mg kg^?1 (T3)]. Results of pot experiments showed that the biomass of Mirabilis jalapa and Tagetes erecta L. had no significant differences among the four treatments, while I. Balsamin showed a decline trend in the biomass with the increase of Cr concentration, probably due to some extent to the poisoning effect of Cr under treatment T2 or T3. Mirabilis jalapa accumulated Cr concentration, with 408.97, 124.97, 630.16 and 57.30 mg kg^?1 in its roots, stems, leaves and inflorescence, respectively. The translocation factor and the bioaccumulation coefficient of Mirabilis jalapa are each greater than 1, indicating that Mirabilis jalapa has the strong ability to tolerate and enrich Cr by biological processes. Comparing accumulation properties of the three ornamental plants, in the amount and allocation, Mirabilis jalapa showed the highest phytoextraction efficiency and could grow well at the high Cr concentration. Our experiments suggest that Mirabilis jalapa is the expected flower species for Cr removal from tannery sludge.