合成生物学助力废弃塑料资源生物解聚与升级再造

石油基合成塑料因高分子量、高疏水性及高化学键能等特性难以被生物降解,在环境中不断累积,由此导致的"白色污染"已经成为一个全球性环境问题。填埋和焚烧是目前塑料垃圾处置最简单、常用的方法,但随之带来的是更为严重的环境二次污染问题。为解决这一问题,开发绿色高效的废塑料资源回收利用技术,从源头解决塑料污染,成为发展塑料循环经济的关键。利用微生物/酶将塑料降解为寡聚体或单体,或进一步转化为高值化学品,因反应条件温和、不产生二次污染等优点将成为废塑料污染治理与资源化的新途径。本文详细介绍了废塑料生物解聚与转化方面的最新研究进展,包括塑料降解微生物和酶的挖掘、混菌/多酶体系的设计与构建、塑料解聚机制,以及塑料解聚物到化学品、能源、材料等高附加值产品的转化。然而,废塑料生物降解过程中仍存在降解元件匮乏、降解效率低、降解物难以利用等技术瓶颈。随着合成生物学的快速发展,利用高通量筛选、进化代谢、生物信息学等先进的生物技术,解析降解关键酶的催化机制、定向设计与改造降解酶、研究混菌体系中菌株间互利共生关系与适配机制、设计并构建不同塑料降解物的代谢通路成为废塑料生物降解研究的重点方向。通过建立废塑料生物降解与高值化利用平台,可为巨量的废塑料资源循环利用提供新的理论基础和关键技术,为我国塑料循环经济发展提供经济、环保、可行的技术支撑。

聚乙烯废弃塑料生物解聚与高值化转化

聚乙烯废弃塑料在环境中日益积累不仅导致视觉污染,也形成潜在的生态污染问题,开发回收和高值化转化聚乙烯废弃塑料的新方法是大势所趋。近年来,废弃塑料生物处理技术因其绿色可持续等优点,成为国内外研究热点,有望成为未来废弃塑料回收管理的重要手段。本文重点综述了聚乙烯废弃塑料生物解聚技术的研究进展,并对聚乙烯废弃塑料化学高值化和生物高值化产品的差异进行分析,在此基础上,总结和展望了目前聚乙烯废弃塑料生物解聚与生物高值化中的挑战以及相应的解决方案,期望联合多学科交叉技术协同生物技术实现聚乙烯废弃塑料的升级循环。

褐煤的分级萃取及生物解聚研究

依次采用去离子水、碱液、正己烷、二氯甲烷、苯和乙醇共沸物和丙酮萃取褐煤样品，得到组分F1～F6，对每个组分进行GC／MS分析，比较各组分结构的差异；利用白腐菌在相同条件下对每种组分进行生物解聚，得到解聚效果最显著的组分，并对此组分在降解前后作红外光谱分析，比较官能团的变化．结果表明：碱液对褐煤的萃取率最高，为30．5％；各组分主要由烷烃、芳香族物质和烃的含氧衍生物组成；碱液分离得到的组分（F2）的生物降解率最高，可达35．59％；生物解聚后芳香族化合物上的一些侧链基团减少甚至消失，且氧的特征峰也随之减少．

木质素的微生物解聚与高值转化

木质纤维素是地球上最丰富的可再生资源。我国每年产生约9亿吨农业秸秆,因得不到有效利用,不仅造成资源浪费,也产生了诸多严峻的环境问题。缺少木质素的高效降解和资源化利用技术是限制木质纤维素产业化的主要瓶颈之一。虽然木质素的降解与转化多年来一直都受到关注,但是由于木质素结构的复杂性及异质性,使其高效利用受限。近年来,微生物具有的"生物漏斗"式转化特性为木质素的高值转化和利用提供了新方向。本文就生物质利用研究以来,微生物在木质素解聚与转化方面的研究历程与最新进展进行了简要的回顾与总结,并初步讨论了目前木质素高值转化面临的机遇与挑战。

Study on Structure and Performance of Starch and Styrene Graft Copolymer

[Objective] The paper was to study the structure and performance of starch and styrene graft copolymer. [Method] The microscopic structure of corn starch and styrene graft copolymer was analyzed by using infrared spectrum and scanning electron microscope, and the property of starch and styrene graft copoly- mer was confirmed through grinding experiment, tensile strength, water absorption rate, hot water resistance properties and enzymatic properties analysis. [Result] The starch and styrene graft copolymer had the properties of thermoplastic and microbial degradation. IConclusion] The starch and styrene graft copolymer is expected to be developed as a biodegradable material.

Usefulness of biodegradable stents constructed of poly-l-lactic acid monofilaments in patients with benign esophageal stenosis

AIM： To report 13 patients with benign esophagea stenosis treated with the biodegradable stent. METHODS： We developed a Ultraflex-type stent by knitting poly-/-lactic acid rnonofilaments. RESULTS： Two cases were esophageal stenosis caused by drinking of caustic liquid, 4 cases were due to surgical resection of esophageal cancers, and 7 cases were patients with esophageal cancer who received the preventive placement of biodegradable stents for postendoscopic mucosal dissection （ESD） stenosis. The preventive placement was performed within 2 to 3 d after ESD. In 10 of the 13 cases, spontaneous migration of the stents occurred between 10 to 21 d after placement. In these cases, the migrated stents were excreted with the feces, and no obstructive complications were experienced. In 3 cases, the stents remained at the proper location on d 21 after placement. No symptoms of re-stenosis were observed within the follow-up period of 7 mo to 2 years. Further treatment with balloon dilatation or replacement of the biodegradable stent was not required. CONCLUSION： Biodegradable stents were useful for the treatment of benign esophageal stenosis, particularly for the prevention of post-ESD stenosis.

Synthesis, Characterization and in vitro Degradation Properties of Poly(Propylene Fumarate-co-Propylene Sebacate) Networks

Poly（propylene fumarate-co-propylene sebacate） （P（PF-co-PS）） was crosslinked with Nvinyl pyrrolidone （N-VP） to form networks. It was investigated as biodegradable bone cement. In this paper, P（PF-co-PS） was synthesized and characterized by ^1H-NMR, FTIR and GPC. The effects of the amount of sebacate segments in P（PF-co-PS） main chains and the quantity of N-vinyl pyrrolidone on the in vitro degradation of the polymer networks were examined. Cylindrical specimens were submerged in phosphate buffered saline （PBS） at 37 ℃ and the pH value of PBS is 7.4 for 10 weeks. The gravimetry and compressive mechanical properties were tested over the degradation period. Networks formed by P（PF-oo-PS）8020/N-VP exhibited higher weight loss and better mechanical properties when compared with poly（propylene fumarate）/N-VP networks. The mechanical properties of P（PF-co-PS）/N-VP can be maintained for a very long time, even for 70 days, the yield strength, fracture strength and compressive modulus are （51.78 ± 2.01） MPa, （52.331 ± 1.84） MPa and （957.78 ± 24.40） MPa, respectively. The results demonstrate that the compressive mechanical properties and degradation velocity can be modulated by the amount of crosslinking agents and sebacate segments along the main chains of copolymers.

Pharmacokinetics and Biodegradation Performance of a Hydroxypropyl Chitosan Derivative

Hydroxypropyl chitosan(HP-chitosan) has been shown to have promising applications in a wide range of areas due to its biocompatibility, biodegradability and various biological activities, especially in the biomedical and pharmaceutical fields. However, it is not yet known about its pharmacokinetics and biodegradation performance, which are crucial for its clinical applications. In order to lay a foundation for its further applications and exploitations, here we carried out fluorescence intensity and GPC analyses to determine the pharmacokinetics mode of fluorescein isothiocyanate-labeled HP-chitosan(FITC-HP-chitosan) and its biodegradability. The results showed that after intraperitoneal administration at a dose of 10 mg per rat, FITC-HP-chitosan could be absorbed rapidly and distributed to liver, kidney and spleen through blood. It was indicated that FITC-HP-chitosan could be utilized effectively, and 88.47% of the FITC-HP-chitosan could be excreted by urine within 11 days with a molecular weight less than 10 k Da. Moreover, our data indicated that there was an obvious degradation process occurred in liver(< 10 k Da at 24 h). In summary, HP-chitosan has excellent bioavailability and biodegradability, suggesting the potential applications of hydroxypropyl-modified chitosan as materials in drug delivery, tissue engineering and biomedical area.

Thermal Decomposition and Kinetics of Mixtures of Polylactic Acid and Biomass during Copyrolysis

Thermal decomposition of polylactic acid （PLA） was studied in the presence of pine wood sawdust （PS）, walnut shell （WS）, corncob （CC） in order to understand the pyrolytic behavior of these components occurring in waste. A thermogravimetric analyzer （TGA） was applied for monitoring the mass loss profiles under heating rate of 10℃·min^-1. Results obtained from this comprehensive investigation indicated that PLA was decomposed in the temperature range 300 -372℃, whereas the thermal degradation temperature of biomass is 183-462℃. The difference of mass loss （AW） between experimental and theoretical ones, calculated as algebraic sums of those from each separated component, is about 17%-46% at 300-400℃. These experimental results indicated a significant synergistic effect during PLA and biomass copyrolysis. Moreover, a kinetic analysis was performed to fit thermogravimetric data, the global processes being considered as one to two consecutive reactions. A reasonable fit to the experimental data was obtained for all materials and their blends.

Biodegradation of DTP and PET Fiber by Microbe

The degradation of diethylene glycol terephthalate (DTP) and polyethylene terephthalate (PET) fiber by microbe was studied.The degree of DTP degradation was determined by High Performance Liquid Chromatography (HPLC) to be more than 90%.The products after degradation of DTP and PET fiber were various.The degradation of DTP can be described by the first-order reaction model.The degradation of PET fiber was found to be little,but surface erosion of PET fiber could be clearly seen from the SEM photographs indicating there occurred some traces of biodegradation on the PET fiber surface.

Pharmacokinetics and Biodegradation of Chitosan in Rats

Chitosan, an excellent biomedical material, has received a widespread in vivo application. In contrast, its metabolism and distribution once being implanted were less documented. In this study, the pharmacokinetics and biodegradation of fluorescein isothiocyanate(FITC) labeled and muscle implantation administrated chitosan in rats were investigated with fluorescence spectrophotometry, histological assay and gel chromatography. After implantation, chitosan was degraded gradually during its distribution to diverse organs. Among the tested organs, liver and kidney were found to be the first two highest in chitosan content, which was followed by heart, brain and spleen. Urinary excretion was believed to be the major pathway of chitosan elimination, yet 80% of chitosan administered to rats was not trackable in their urine. This indicated that the majority of chitosan was degraded in tissues. In average, the molecular weight of the degradation products of chitosan in diverse organs and urine was found to be <65 k Da. This further confirmed the in vivo degradation of chitosan. Our findings provided new evidences for the intensive and safe application of chitosan as a biomedical material.

Fabrication of a Knitted Biodegradable Stents for Tracheal Regeneration

Endoluminal stents for reinforcement and regeneration of human trachea have been developed by weft-knitting method on a small-diameter circular knitting machine. The constituent materials of the stent are Polyglactin, Polypropylene and Chitosan with Polyglactin and Polypropylene plate-stitched fabric acting as backbone while chitosan as matrix, respectively. The fabrication procedures including knitting and coating are described in this paper. Mechanical and animal tests have been carried out to evaluate the mechanical properties of the stents.

Degradation of polyvinyl-alcohol wastewater by Fenton’s reagent: Condition optimization and enhanced biodegradability

The pretreatment of refractory polyvinyl-alcohol （PVA） wastewater with low value of CODcr by Fenton＇s reagent was investigated to enhance the biodegradabilily. The effects of operating conditions such as pH of the solution, Fe2＋ dosage, H2O2 dosage, reaction time and initial PVA concentration on the removal efficiency of CODCr were discussed. It is demonstrated that the optimum value of pH for removal of CODcr is 5 and the most suitable dosages of H2O2 （2%） and FeSO4 （10 mg/L） are 5% and 8.0%, respectively. When the initial CODcr value of the PVA water is 760 mg/L, the favorable reaction time is 110 min. Under these optimum conditions, the removal ratio of CODcr is 58.6% 61.4%, and the value of biodegradability （CODB/CODcr） increases markedly from 8.9% 9.7% to 62.6% 68.3%.

Process engineering in electrochemical energy devices innovation

This review focuses on the application of process engineering in electrochemical energy conversion and storage devices innovation. For polymer electrolyte based devices, it highlights that a strategic simple switch from proton exchange membranes(PEMs) to hydroxide exchange membranes(HEMs) may lead to a new-generation of affordable electrochemical energy devices including fuel cells, electrolyzers, and solar hydrogen generators. For lithium-ion batteries, a series of advancements in design and chemistry are required for electric vehicle and energy storage applications. Manufacturing process development and optimization of the LiF eP O_4/C cathode materials and several emerging novel anode materials are also discussed using the authors' work as examples.Design and manufacturing process of lithium-ion battery electrodes are introduced in detail, and modeling and optimization of large-scale lithium-ion batteries are also presented. Electrochemical energy materials and device innovations can be further prompted by better understanding of the fundamental transport phenomena involved in unit operations.

WAXD and FTIR Studies of Electron Beam Irradiated Biodegradable Polymers

Poly（L-lactic acid） （PLLA） and poly（e-caprolactone） （PCL） have been receiving much attention lately due to their biodegradability in human body as well as in the soil, also due to their biocompatibility, environmentally friendly characteristics and non-toxicity. Morphology of biodegradable polymers affects the rate of their biodegradation. A polymer that has high degree of crystallinity will degrade at a slower rate due to the inherent increased stability. PCL homopolymer crosslinking degree increases with increasing doses of high energy radiation. On the other hand, the irradiation ofPLLA homopolymer promotes mainly chain-scissions at doses below 250 kGy. In the present work, twin screw extruded films of PLLA and PCL biodegradable homopolymers and 50：50 （w：w） blend were electron beam irradiated using electron beam accelerator Dynamitron （E = 1.5 MeV） from Radiation Dynamics, Inc. at doses in the range of 50 kGy to 103 kGy in order to evaluate the effect of electron beam radiation. Wide-angle X-ray diffraction （WAXD） patterns of non irradiated and irradiated samples were obtained using a diffractometer Rigaku Denki Co. Ltd., Multiflex model; and Fourier transform infrared spectroscopy （FTIR） spectra was obtained using a NICOLET 4700, attenuated total reflectance （ATR） technique. By WAXD patterns of as extruded non irradiated and irradiated PLLA it was verified broad diffusion peaks corresponding to amorphous polymer. There was a slight increase of the mean crystallite size of PCL homopolymer with increasing radiation dose. PCL crystalline index （CI） decreased with radiation dose above 500 kGy. But then, PLLA CI increased with radiation dose above 750 kGy. From another point of view, PLLA presence on the 50：50 blend did not interfere on the observed mean crystallite size increase up to 250 kGy. From 500 kGy to 103 kGy the crystallite size of PCL was a little bigger in the blend than the homopolymer. In contrast, FTIR results have shown that this technique was not sensitive enough to observe the degradation promoted by ionizing radiation of the studied homopolymers and blends, and neither on the miscibility of the blends.

Infrared Spectroscopy for Studying Foods and Biodegradable Packaging

The results of study of foods and biodegradable film structure with the use of infrared spectroscopy （IR spectra） are presented. For the first time detailed decodings of IR spectra of some foods and biodegradable film packaging materials are shown. Interpretation of the spectra of basic biopolymers of foods and biodegradable films is given. It is corroborated with the help of IR spectra that the chemical reactions in biopolymers when heated to 130 ~C do not occur, which makes it possible to use biologically valuable raw materials. Furthermore, the expediency of use of IR spectroscopy for studying changes in foods and films produced on biopolymer base is established. IR spectroscopy is a fast method that allows you to monitor changes that occur with the raw materials in the technological process. Previously, IR spectroscopy was used to identify the compounds in chemical synthesis. This study shows that IR spectra can be used for study of foods and biodegradable film structure.

PREPARATION AND PROPERTIES OF POLY(LACTIC ACID-CO-GLYCOL TEREPHTHALIC ACID)COPOLYESTER

To obtain a kind of biodegradable polymer material with satisfactory properties, a new biodegradable copolyester poly（lactic acid-co-glycol terephthalate） （PETA）, was synthesized from three monomers of lactic acid, glycol and terephthalic acid. The resulting copolyesters, PETA, were characterized by FT-IR, ^1H-NMR, DSC, TGA and by the ways of weight loss rate to characterize their biodegradability. The findings in this work indicated that, the Tins and Tas of copolyesters PETA increased with increasing contents of the terephthalic acid units. From the biodegradation tests in natural soil, boiling water, acid buffer solution and alkali buffer solution, it was shown that the biodegradability of copolyesters PETA decreased with increasing contents of the terephthalic acid units.

STUDIES ON GRAFT COPOLYMERIZATION OF DL-LACTIDE ON CORN STARCH AND BIODEGRADABILITY OF THE COPOLYMERS

The starch/D,L-lactide graft copolymers were synthesized by reacting D,L-lactide with corn starch in N,N-dimethylacetamide (DMAM) in the presence of triethylamine (NEt3) and anhydrous lithium chloride. The effect of reaction time and the molar ratio of D,L-lactide to glucose structural unit of starch on monomer conversion(C%), graft (G%) and graft efficiency (GE%) were studied. The C%, G% and GE% could approach 37.3%,179.7% and 68.0%, respectively when the molar ratio of D,L-lactide to glucose structural unit of starch is 10:1 and the graft copolymerization was carried out at 80-85℃ for 4 hours under nitrogen atmosphere. The Fourier transforms infra-red (FTIR) spectroscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) spectroscopy were used in order to characterize the graft copolymers. FTIR spectra show that absorption band at 1740 cm-1 confirmed the formation of ester bond, indicating the starch /D,L-lactide graft copolymers were produced, the DSC characteristic results show the melting temperature of the graft copolymer were elevated slightly as the molar ratio of D,L-lactide to glucose structural units of starch increased and the X-ray diffraction spectra show the synthesized graft copolymers were amorphous. The degradability of graft copolymer was tested with the aid of acid, alkali and microbe such as bacillus subtilis and staphylococcus aureus. The results of water resistance show the graft copolymer produced can be used as a component of impermeable coating for cardboard.

Preparation and Characterization of Nimodipine-loaded Methoxy Poly(ethylene glycol)-poly(lactic acid) Diblock Copolymer Nanoparticles

Amphiphilic diblock copolymers, methoxy poly （ ethylene glycol）-poly（lactic acid） （MePEG-PLA）, were synthesized from monomers of DL-lactide and methoxy poly （ethylene glycol） by a ring opening bulk polymerizatiou in the presence of stannous octoate. Their chemical structure and physical properties were investigated using FTIR, NMR, GPC, and fluorescence spectroscopy. To estimate the feasibility as colloidal drug carrier, nimodipine （ND） was loaded into MePEG-PLA block copolymer nanoparticles by phaseseparation/dialysis method. The mean diameter and drug loading efficiency of ND-loaded MePEG-PLA copolymer nanoparticles depended ou PLA/MePEG block composition of the copolymer and drug/polymer feed ratio in preparatiou. NMR study confirmed that nimodipine was entrapped into the hydrophobic inner core of MePEG-PLA copolymer nanoparticles and hydrophilic PEG chains were located ou the surface of the drug-loaded polymer nanoparticles. In vitro release experiments exhibited the sustained release behavior of nimodipine from MePEG-PLA copolymer nanoparticles, without any burst effect.

Study on Kinetics of Dissolving Biomass Using Sodium Hypochlorite in the Recovery of Poly-β-hydroxybutyrate

The effects of sodium hypochlorite concentration in the recovery of poly-β-hydroxybutyrate (PHB) are investigated. A simple reaction equation and a mathematical model describe the reaction kinetics. Results showed that the stoichiometric coefficient increases with increasing CAO/CBO, where CAO is the concentration of the active chlorine at t = 0 and CBO is the initial concentration of the non-PHB materials.