The Properties of Poly(<Emphasis Type="SmallCaps">l</Emphasis>-Lactide) Prepared by Different Synthesis Procedure

Different synthesis methods were applied to determine optimal conditions for polymerization of (3S)-cis-3,6-dimethyl-1,4-dioxane-2,5-dione (l-lactide), in order to obtain poly(l-lactide) (PLLA). Bulk polymerizations (in vacuum sealed vessel, high pressure reactor and in microwave field) were performed with tin(II) 2-ethylhexanoate as the initiator. Synthesis in the vacuum sealed vessel was carried out at the temperature of 150 °C. To reduce the reaction time second polymerization process was carried out in the high pressure reactor at 100 °C and at the pressure of 138 kPa. The third type of rapid synthesis was done in the microwave reactor at 100 °C, using frequency of 2.45 GHz and power of 150 W at the temperature of 100 °C. The temperature in this method was controlled via infrared system for in-bulk measuring. The solution polymerization (with trifluoromethanesulfonic acid as initiator) was possible even at the temperature of 40 °C, yielding PLLA with narrow molecular weight distribution in a very short period of time (less than 6 h). The obtained polymers had the number-average molecular weights ranging from 43,000 to 178,000 g mol⁻¹ (polydispersity index ranging from 1 to 3) according to the gel permeation chromatography measurements. The polymer structure was characterized by Fourier transform infrared and NMR spectroscopy. Thermal properties of the obtained polymers were investigated using thermogravimetry and differential scanning calorimetry.     

Poly(hydroxyalkanoate) Biosynthesis from Crude Alaskan Pollock (Theragra chalcogramma) Oil

Six strains of Pseudomonas were tested for their abilities to synthesize poly(hydroxyalkanoate) (PHA) polymers from crude Pollock oil, a large volume byproduct of the Alaskan fishing industry. All six strains were found to produce PHA polymers from hydrolyzed Pollock oil with productivities (P; the percent of the cell mass that is polymer) ranging from 6 to 53% of the cell dry weight (CDW). Two strains, P. oleovorans NRRL B-778 (P = 27%) and P. oleovorans NRRL B-14682 (P = 6%), synthesized poly(3-hydroxybutyrate) (PHB) with number average molecular weights (M_n) of 206,000 g/mol and 195,000 g/mol, respectively. Four strains, P. oleovorans NRRL B-14683 (P = 52%), P. resinovorans NRRL B-2649 (P = 53%), P. corrugata 388 (P = 43%), and P. putida KT2442 (P = 39%), synthesized medium-chain-length PHA (mcl-PHA) polymers with M_n values ranging from 84,000 g/mol to 153,000 g/mol. All mcl-PHA polymers were primarily composed of 3-hydroxyoctanoic acid (C_8:0) and 3-hydroxydecanoic acid (C_10:0) amounting to at least 75% of the total monomers present. Unsaturated monomers were also present in the mcl-PHA polymers at concentrations between 13% and 16%, providing loci for polymer derivatization and/or crosslinking. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.     

Conjugation of Soybean Oil and It’s Free-Radical Copolymerization with Acrylonitrile

The conjugated soybean oil was synthesized through the isomerization reaction of soybean oil to transformed the structure of linoleic acid into conjugated linoleic acid structure, and Rhodium complexes (RhCl(Pph₃)₃) was used as catalyst. The efficiency on the conjugation of catalyst RhCl (Pph₃)₃, tin dichloride dehydrate (SnCl₂·2H₂O) and triphenylphosphine (Pph₃) were evaluated. The results showed when RhCl(Pph₃)₃, SnCl₂·2H₂O and Pph₃ are 9.25, 9.0 and 13.1 mg in 100 g soybean oil respectively, the highest conversion of conjugation achieved 96%. The free radical copolymerization of conjugated soybean oil with acrylonitrile (AN) and dicyclopentadiene (DCP) was studied. AIBN was used as the initiator. FT-IR and ¹H-NMR results indicates that the conjugated soybean oil with AN and DCP did occur free radical copolymerization with the initiator AIBN. The product is light yellow powder. The thermal properties of the soy-based copolymer were investigated by TG and DSC. The initial degradation temperature of polymers is higher then 250 °C.     

A Novel Biodegradable Fluorine-Containing Copolymer Surfactant

A novel fluorine-containing copolymer surfactant was synthesized via free radical copolymerization from maleic anhydride and rapeseed oil firstly, and then followed by an esterification reaction with dodecafluoro heptanol. The reaction progresses were monitored on-line by FTIR and the copolymerization was characterized by molecular weight (GPC) analysis. Simultaneously, the surface tension and critical micelle concentration (CMC) together with the biodegradability of the fluorine-containing copolymer surfactant were investigated in detail. The results indicate that this fluorine-containing surfactant with Mw of 66000 g/ mol and Mn of 38800 g/mol shows a strong surface tension lowering ability, the CMC is 0.1 g/L, the surface tension value at the CMC (γ_CMC) is 22.5 mN m⁻¹ and less than the corresponding copolymeric hydrocarbon surfactant; the evaluation of biodegradability indicates that the biological respiration curve of the fluorine-containing copolymer surfactant with concentration of 1000 mg/L is above the endogenous respiration curve; the BOD₅/COD value is higher than 0.45; the COD and TOC removal ratios after 5 days of biodegradation reach 91.0 and 89.4%, respectively, showing good biodegradability and environmental-friendly feature.     

Polymerization of l-lactide with SnCl2: A Low Toxic and Eco-friendly Catalyst

Polymerizations of l-lactide catalyzed either by neat SnCl₂ or by SnCl₂?+?difunctional cocatalysts were conducted in bulk at 180, 160 and 140 °C with variation of the Lac/Cat ratio and time. With neat SnCl₂ poly(L-lactide) having weight average molecular weights (uncorrected M_w’s) up to 190 000 g mol^?1 were obtained mainly consisting of linear chains. Addition of salicylic acid or 1,1-bisphenol yielded a higher fraction of cyclic polylactides but lower molecular weights. Furthermore, SnCl₂ was compared with Bu₂SnCl₂ and various other metal chlorides and the best results were obtained with SnCl₂. With ethyl L-lactate as initiator SnCl₂-catalyzed ROPs were performed at 120 °C and the lac/initiator ratio was varied. All these experiments were conducted under conditions allowing for comparison with ROPs catalyzed with neat Sn(II)-2-ethyhexanoate. Such a comparison was also performed with ε-caprolactone as monomer.

     

Sonophotocatalytic Degradation of Chitosan in the Presence of Fe(III)/H2O2 System

The degradation of chitosan by means of ultrasound irradiation and its combination with homogeneous photocatalysis (photo-Fenton) was investigated. Emphasis was given on the effect of additive on degradation rate constants. 24 kHz of ultrasound irradiation was provided by a sonicator, while an ultraviolet source of 16 W was used for UV irradiation. To increase the efficiency of degradation process, degradation system was combined with Fe(III) (2.5 × 10⁻⁴mol/L) and H₂O₂ (0.020–0.118 mol/L) in the presence of UV irradiation and the rate of degradation process change from 1.873 × 10⁻⁹−6.083 × 10⁻⁹ mol^1.7 L s⁻¹. Photo-Fenton process led to complete chitosan degradation in 60 min with the rate increasing with increasing catalyst loading. Sonophotocatalysis in the presence of Fe(III)/H₂O₂ was always faster than the respective individual processes. A synergistic effect between ultrasound and ultraviolet irradiation in the presence of Fenton reagent was calculated. The degraded chitosans were characterized by X-ray diffraction (XRD), gel permeation chromatography (GPC) and Fourier transform infrared (FT-IR) spectroscopy and average molecular weight of ultrasonicated chitosan was determined by measurements of intrinsic viscosity of samples. The results show that the total degree of deacetylation (DD) of chitosan change, partially after degradation and the decrease of molecular weight led to transformation of crystal structure. A negative order for the dependence of the reaction rate on total molar concentration of chitosan solution within the degradation process was suggested. Results of this study indicate that the presence of catalyst in the reaction medium can be utilized to reduce molecular weight of chitosan while maintaining the power of irradiated ultrasound and degree of deacetylation.     

Morphological and Thermal Characterization of Linseed-Oil Based Polymers from Cationic and Thermal Polymerization

Linseed oil-based polymers have been synthesized via cationic and thermal polymerization and characterized through various techniques, such as SEM, DMA, DSC and TGA. The morphology of the polymer samples after extraction reveals the smooth structure of the polymer matrix. With an increase in oil content, the morphology is observed to be more loosely bound. With an increase in linseed oil content in the samples, the room temperature storage modulus (E′) varies from 10.4 × 10⁷ to 1.8 × 10⁷ Pa. The glass transition temperatures measured through DMA of the cationic samples ranges from 70 to −6 °C and the crosslink densities range from 18.4 × 10³ to 3.4 × 10³ mol/m³. The glass transition temperatures of the thermal samples range from 106 to −4 °C and the crosslink densities range from 7.7 × 10³ to 2.4 × 10³ mol/m³. The TGA results show three stages of degradation of the polymer samples and it is also revealed that these polymers are stable up to 200 °C, showing negligible decomposition.     

Palm Oleic Acid Based Alkyds: Effect of the Fatty Acid Content on the Polyesterification Kinetics

The kinetic behavior of polyesterification of the alkyd resins synthesized using glycerol and phthalic anhydride modified with oleic acid from the palm oil at temperatures between 120 and 240 °C was studied. Three alkyds having oleic acid contents of 28, 40, and 65% were prepared by employing fatty acid method. The extent of the polyesterification reaction and average degree of polymerization were monitored by determining the acid number of the aliquot of the reaction mixture at various intervals of time and by measuring the volume of water evolved. Kinetic studies revealed that initial reaction rates followed a second-order kinetics up to certain limit and thereafter deviations were observed. The extent of reaction varied from 77.4 to 86.3% before deviation for all the three samples and exhibited a considerable degree of conversion. The second-order rate constants calculated from the linear part were found to be of the order of 10⁻⁵ g (mg KOH)⁻¹ min⁻¹. Molecular weight of the alkyd samples was determined by GPC; number average molecular weight of the alkyds ranged from 980 to 2,070.     

Comparative Investigations on Optimum Polymerization Conditions for the Synthesis of a Sustainable Poly(Lactic Acid)

The development of synthetic biodegradable polymers using solvent free polymerization has a unique potential to be used as sustainable polymers in biomedical applications. The aim of this work was to synthesize and characterize a sustainable class of poly(lactic acid) (PLA) under different operating conditions via direct polycondensation of lactic acid (LA). Several parameters were tested including the absence of solvents and catalysts on the polymerization, in addition to polymerization temperature and time. Polymerization conditions were evaluated using response surface method (RSM) to optimize the impact of temperature, time, and catalyst. Results showed that molecular weight (M_w) of PLA increased with increasing polymerization time. Highest M_w of 28.4 kD with relatively a broad polydispersity 1.9 was achieved at polymerization temperature 170?°C at 24 h in the free solvent polymerization. This led to a relevant inherent viscosity of 0.37 dl/g. FTIR spectra exhibited a disappearance of the characteristic peak of the hydroxyl group in LA at 3482 cm^?1 by increasing the intensity of carbonyl group. The ¹H nuclear magnetic resonance (NMR) exhibited the main chain at 5.22 ppm and the signal of methyl proton at 1.61 ppm as well as a signal at 4.33 and 1.5 assigned to the methane proton next to the terminal hydroxyl group and carboxyl group respectively. Meanwhile, the PLA synthesized with a catalyst [Sn(Oct)₂] in a free solvent demonstrated comparatively high thermal transition properties of glass transition, melting, and crystallinity temperatures of 48, 106, and 158?°C, respectively. These results are of significant interest to further expand the use of PLA in biomedical applications.     

Characterization and Release Kinetics of Allylthiosufinate and its Transforments from Poly(d,l-Lactide) Microspheres

In this work was described poly(d,l-lactide) microwave synthesis using tin(II) 2-ethylhexanoate initiated ring-opening polymerization. Polymerization was performed at 100 °C with monomer to initiator molar ratio ([M]/[I]) of 5,000 in 30 min. The achieved number average molar mass of obtained polymers (determined by gel permeation chromatography) was 102,320 g/mol, with the polydispersion index, Q, 2.80. Structural characterization was performed by FT-IR spectroscopy followed characteristic bands. For applicative purposes the obtained polymer was purified during the procedure of microsphere preparation. Biodegradable microspheres prepared from poly(d,l-lactide) have been widely studied in recent years and have become well established controlled drug delivery systems. In this work microspheres were loaded with allyl thiosulfinate (allicin) and its transforments products (ajoene and vinyldithiine), as pharmacological active substances. The morphology of the microspheres was analyzed using a scanning electron microscope. Allicin was synthesized by acid oxidation of allyl disufide and purification of obtained products by liquid–liquid extraction with diethyl ether. Obtained allicin, purity 73%, was transformed using microwave in acetone solution, at solvent boiling temperature, for 5 min. For the quality and quantity analysis of allicin and its transformation process was used LC/MS chromatography. (E)- and (Z)-ajoene were detected at retention time 3.1 and 3.3 min, respectively, whence 3-vynil-4H-1,2-dithiine and 2-vynil-4H-1,3-dithiine were detected at 4.3 and 4.8 min, respectively. Retention time of allicin was 2.93 min, according to liquid chromatography results. HPLC method was used for assessment of pharmaceutical substances (alicine and alicine transforments) releasing from microspheres at room temperature in solutions with different pH (pH = 3 and pH = 8) for 24 h.     

Changes in carbonyl index and average molecular weight on embrittlement of enhanced-photodegradable polyethylenes

Weathering behavior of two types of enhanced-photodegradable polyethylenes was studied using FTIR spectroscopy, tensile property changes, and gel-permeation chromatography to monitor structural changes accompanying photodegradation. Changes in elongation at break and carbonyl index during degradation showed a strong correlation with the average molecular weight of the polymers. At the point of embrittlement, the highest extent of degradation measured using tensile properties, the number-average molecular weights for both polymers were in the 10⁴ g/mol range. Facile biodegradation is not expected of polyethylenes of this degree of polymerization.     

Biodegradable Polymers from 5-Hydroxylevulinic Acid: 1. Synthesis and Characterization of Poly(5-hydroxylevulinic acid)

As an attempt to synthesize new biodegradable polymers from renewable cellulose resources, melt polycondensation of 5-hydroxylevulinic acid (5-HLA) was reported for the first time. The resulting product, poly(5-hydroxylevulinic acid) (PHLA), was synthesized and characterized with GPC, FTIR, ¹H NMR and DSC. The in vitro degradation behaviors in phosphate-buffered saline (PBS) and in deionized water (DW) were also examined. The molecular weight of PHLA is not high (several 1,000s), but it possesses unordinary high glass transition temperature (as high as 120 °C). This is very different from existing aliphatic polyesters that usually have T _gs lower than 60 °C. The high T _g is attributed to the formation of inter- and/or intramolecular hydrogen bonds due to a characteristic keto–enol tautomerism equilibrium in the polymer structure. PHLA readily degraded hydrolytically in aqueous media.     

Suspension Polymerization of Poly(l-lactide-co-p-dioxanone) in Supercritical Carbon Dioxide

Biodegradable copolymers of l-lactide(l-LA) and p-dioxanone(PDO) were synthesized in supercritical carbon dioxide (scCO₂) with stannous octoate as the ring-opening catalyst and a fluorocarbon polymer surfactant as an stabilizer. Fine powderous products were achieved when more than 90% (w/w) l-LA was fed. Scanning electron micrographic images and laser diffraction particle size analysis of the products showed the mean diameter of particles greatly increased as the content of PDO increased. The obtained polymers had the number-average molecular weights ranging from 15,000 to 26,000 g mol⁻¹ (polydispersity index ranging from 1.3 to 2.1) according to the gel permeation chromatography measurements. The polymer structure was characterized by NMR spectroscopy, indicating the formation of copolymers. Thermal properties of the obtained polymers investigated using differential scanning calorimetry showed that the morphology of products was directly relevant to the crystallinity of the copolymers. The polymerization of l-LA and PDO copolymers in scCO₂ is also proposed as a novel production technique for high-purity, biodegradable polymers.     

1,3-Propanediol Production Potential by a Locally Isolated Strain of Klebsiella Pneumoniae in Comparison to Clostridium Beijerinckii NRRL B593 from Waste Glycerol

The fermentative production of 1,3-propanediol (1,3-PDO) by Klebsiella pneumoniae under different initial substrate concentrations (between 5 and 110 g/L) was investigated. It was found that glycerol was almost 100% utilized and 1,3-PDO production increased up to 20 g/L of influent substrate concentration, but there was a significant decrease in both glycerol consumption and 1,3-PDO production at substrate concentrations exceeding 20 g/L. Furthermore, pH control was essential, and a lack of pH control negatively effects of 1,3-PDO production. In the second part of the study, two microorganisms, namely Clostridium beijerinckii NRRL B593 and K. pneumoniae were comparatively studied in terms of their 1,3-PDO productivity under pH controlled conditions. Higher 1,3-PDO production was achieved under pH controlled fermentation conditions (pH = 7) for both microorganisms. Even though the two microorganisms had almost the same 1,3-PDO yield (0.60 mol/mol for C. beijerinckii, 0.61 mol/mol for K. pneumoniae) at the end of fermentation period, K. pneumoniae completed the 1,3-PDO production in one-third of the time (t = 8 h with a productivity of 1.34 g/L/h) than C. beijerinckii (t = 24 h). The results of this study clearly indicated that a substrate inhibition is a challenge that needs to be studied further for higher productivities.     

Soybean Oil-Based Photo-Crosslinked Polymer Networks

Novel soybean oil-based crosslinked polymer networks were prepared by UV photopolymerization and their mechanical properties were evaluated. Poly(ethylene glycol) diacrylate (PEGDA) and biodegradable poly(ε-caprolactone) diacrylate (PCLDA) were synthesized and used as crosslinking agent to form crosslinked polymer networks by UV-initiated free-radical polymerization with acrylated epoxidized soybean oil (AESO). The synthesis of acrylate end-capped macromers was confirmed using FT-IR and ¹H NMR spectroscopic techniques. Photopolymerization time, the composition of reaction mixture, and the type and length of crosslinking agent were changed to obtain crosslinked polymer networks with various mechanical properties. Polymers prepared from AESO and PCL degraded 6% of the initial weight in 24 days in phosphate buffer solution (pH 7.2) containing lipase enzyme. These potentially biodegradable and biocompatible polymers can be used as ecofriendly materials for biomedical and other applications to replace the existing petroleum-based polymers currently used.     

Material Properties and Influence of Molecular Weight and Testing Rate on Adhesion Properties of Epoxidized Natural Rubber-Based Adhesives

The effect of molecular weight and testing rate on peel and shear strength of epoxidized natural rubber (ENR-50)-based adhesive was investigated using petro resin as the tackifier. Toluene and polyethylene terephthalate were used as the solvent and substrate respectively. Peel and shear strength were determined by a Llyod Adhesion Tester operating at different rates of testing. Result shows that peel strength and shear strength increases up to an optimum molecular weight of 4.2 × 10⁴ g/mol of ENR-50. This observation is attributed to the combined effects of wettability and mechanical strength of rubber for peel strength. For shear strength, it is ascribed to the optimum cohesive and adhesive strength. Both peel strength and shear strength increases with increasing rate of testing, an observation which is associated to the viscoeslastic response of the adhesive. Thermal study, SEM and FTIR study confirms the miscibility of tackifier with ENR-50.     

Enzyme-Based Vinyl Polymerization

In vitro enzyme-mediated polymerization of vinyl monomers is reviewed. Oxidoreductase enzymes have been used for the polymerization of styrene, derivatives of styrene, acrylates, and acrylamide in water and water-miscible co-solvents. Kinetic and mechanistic studies revealed that a ternary system (horseradish peroxidase, H₂O₂, initiator, or -diketone) is required for efficient polymerization and the initiator controls the polymer characteristics.     

Polyethylene conversion by partial oxidation in supercritical water

This paper gives the results of partial oxidation experiments of polyethylene (PE) in supercritical water (SCW). The experiments were carried out at a reaction temperature of 693K and a reaction time of 30 min using 6 cm³ of a batch-type reactor. The loaded sample weight was 0.3 g and there was 2.52 g water (0.42 g/cm³). The ratio of oxygen atoms to carbon atoms was 0.3. The results show a significant CO formation in O₂–SCW, and the 1-alkene/n-alkane ratio in partial oxidation was higher than that in SCW pyrolysis. These results suggest the possibility of the hydrogenation of hydrocarbon through partial oxidation followed by a water–gas shift reaction. Received: July 19, 2000 / Accepted: September 28, 2000     

Itaconic Acid Grafted Starch Hydrogels as Metal Remover: Capacity,Selectivity and Adsorption Kinetics

Hydrogels were synthesized by free radical graft copolymerization of itaconic acid (IA) onto corn starch (S-g-IA). For this purpose, potassium permanganate (KMnO₄)-sodium bisulfite (NaHSO₃) was used as redox initiation system. The formation of grafted starches was confirmed by Fourier transform infrared spectroscopy, wide angle X-ray scattering, thermogravimetric analysis and scanning electron microscopy. The effect of monomer concentration, neutralization, addition of crosslinking agent, N,N-bismetilenacrilamide (MBAm), and initiator concentration on grafting efficiency and adsorption capacity of the starch hydrogels was investigated. It was demonstrated that the introduction of carboxyl and carbonyl groups promoted starch hydration and swelling. Grafting degree increased with the decrease of monomer concentration, increase of initiator concentration, grade of neutralization and the addition of MBAm without neutralization. Remarkably the resulting materials exhibited water absorption capacities between 258 and 1878% and the ability to adsorb metal ions. It was experimentally confirmed the metal uptake, obtaining the higher adsorption capacity (q _e  = 35 mg/g) for the product prepared with the pre-oxidation and lower initiator concentration. The removal capacity order was Pb²⁺>Ni²⁺>Zn²⁺>Cd²⁺. Moreover, the experimental kinetic and the equilibrium adsorption data for Ni²⁺ and Pb²⁺ were best fitted to the pseudo-second order and Freundlich isotherm models, respectively. This work describes for the first time the preparation of metal removal hydrogels based on starch and itaconic acid using the pair redox system KMnO₄/NaHSO₃, which avoids the starch hydrolysis and allows itaconic acid grafting incorporation without the requirement of more reactive comonomers.     

Leaching behavior of copper from waste printed circuit boards with Brønsted acidic ionic liquid

In this work, a Brønsted acidic ionic liquid, 1-butyl-3-methyl-imidazolium hydrogen sulfate ([bmim]HSO₄), was used to leach copper from waste printed circuit boards (WPCBs, mounted with electronic components) for the first time, and the leaching behavior of copper was discussed in detail. The results showed that after the pre-treatment, the metal distributions were different with the particle size: Cu, Zn and Al increased with the increasing particle size; while Ni, Sn and Pb were in the contrary. And the particle size has significant influence on copper leaching rate. Copper leaching rate was higher than 99%, almost 100%, when 1 g WPCBs powder was leached under the optimum conditions: particle size of 0.1–0.25 mm, 25 mL 80% (v/v) ionic liquid, 10 mL 30% hydrogen peroxide, solid/liquid ratio of 1/25, 70 °C and 2 h. Copper leaching by [bmim]HSO₄ can be modeled with the shrinking core model, controlled by diffusion through a solid product layer, and the kinetic apparent activation energy has been calculated to be 25.36 kJ/mol.