Molecular dynamics of chiral semi-crystalline poly(R)-(3-hydroxyalkanoates)

The inversion-recovery cross-polarization (IRCP) sequence used for measuring cross-relaxation time (T_CH) is modified to obtain signals that show exponential or spin-lock (SL) decay to zero. The new sequence may, therefore, be analogously abbreviated as SLCP. Poly(R)-(3-hydroxybutyrate-co-3-hydroxyhexanoate) {P(HB-HHx) (85:15)} is found to be more mobile than poly(R)-(3-hydroxybutyrate) {PHB} in the crystalline regions. The molecular-level evidence by solid state nuclear magnetic resonance (NMR) that the P(HB-HHx) chain is more flexible than PHB is echoed by the dynamic frequency sweep measurements of the biopolymer melts, which show that the PHB melt has an unusual rheological response with the dynamic loss moduli dominating the storage moduli at all frequencies. This is most likely to be caused by the local anisotropic melt structures due to the long persistence length of PHB in the melt. Upon cooling the PHB melt to the solid state, such high levels of anisotropy may be frozen into the solid causing lower chain mobility, and hence giving rise to lower toughness. The incorporation of longer side chain unit to the main chain gives rise to a dynamic rheological response in P(HB-HHx) similar to that of an isotropic melt. This is believed to be due to the enhanced chain flexibility, and hence reduced persistence length. This further allows P(HB-HHx) to be processed into a more uniform isotropic morphology, and hence with improved mechanical toughness.     

Microstructure of copoly(3-hydroxyalkanoates) produced in the anaerobic–aerobic activated sludge process

The sequence structures of bacterially synthesized copoly(3-hydroxyalkanoates), isolated from the sludge developed in the anaerobic–aerobic waste-water treatment process containing propionate as a carbon source, were analysed by ¹³C NMR spectroscopy. These copolyesters were composed of four different monomer units, 3-hydroxybutyrate, 3-hydroxyvalerate, 3-hydroxy-2-methylbutyrate and 3-hydroxy-2-methylvalerate. By using water/acetone mixed solvent, one of the copolyester samples was fractionated into fractions by differences in average molecular weights as well as in monomer compositions. The carbonyl carbon resonances, split due to differences in diad sequences, were analysed on the basis of Bernoullian statistics. It is suggested that these copolyesters were mixtures of random copolymers with different monomer compositions.     

Growth behavior of Bacillus thuringiensis and production of poly(3-hydroxyalkanoates) on different organic substrates

Summary Bacillus thuringiensis is known as a bacterial species capable of the production of short side chain poly--hydroxyalkanoates (PHAs). In the present work it was shown that the organism is also capable of producing longer side chain PHAs under appropriate conditions. The microorganism was grown separately on glucose, nonanoic acid, and a mixture of glucose, peptone and casein in attempts to obtain poly--hydroxyalkanoates with varying lengths of the pendent alkyl group in the -position of the polymer repeat unit. The growth on glucose resulted in the formation of poly-3-hydroxybutyrate, (PHB), which is a very common bacterial storage polymer, while the utilization of nonanoic acid resulted in the formation of a copolymer consisting of 3-hydroxynonanoate and 3-hydroxyheptanoate units (PHN/PHH), which is the usual product of the microbial utilization of this particular carbon source by Pseudomonas oleovorans.     

Chemical synthesis and characterization of POSS-functionalized poly[3-hydroxyalkanoates]

A polyhedral oligomeric silsesquioxane containing seven isobutyl groups and one mercaptopropyl group (POSS-SH) was linked via a free radical addition reaction to the side-chain double bonds of bacterial poly[3-hydroxyalkanoate-co-3-hydroxyalkenoate], (PHAE). PHAE with 11.5, 55, 78, and 97 mol% of double bonds were used to produce a series of inorganic-organic hybrid materials, PHAE-POSS, with increasing amounts of POSS. The reactions proceeded with high yields and limited side reactions, confirmed with NMR and GPC experiments. X-ray diffraction and ¹³C solid-state NMR analysis of these nanocomposite materials suggested the favoured crystallization of POSS, with PHAE functioning as a non-crystalline combining matrix. This is in contrast to blends of POSS-SH and PHAE, where incompatibility occurred and the two components crystallized independently. The covalent links between PHAE and POSS imposed spatial constraint which resulted in disordered crystalline POSS domains and limited crystal sizes. With increasing POSS content, the appearance of these POSS-based biopolyesters changed from non-sticky and elastic to brittle and glass-like. The covalent linking of POSS-SH to PHAE increased the heat stability such as glass transitions, and melting points could be tailored between 48 and 120 °C.     

多聚羟基烷酸的发酵生产研究进展

多聚羟基烷酸（PHA）是一类有良好应用前景的生物可降解塑料，为降低其生产成本，国内外科研工作者进行了大量的研究，本文着重对PHA的发酵生产和提取工艺进行了介绍。     

Comparison of selected methods for downstream processing in the production of bacterial lipase

Enzymes are of growing interest to the chemical and pharmaceutical industries as highly specific biocatalysts. An obstacle to a large-scale application of such proteins is the expenditure on recovery operations which can amount up to 80% of the total production costs. Therefore, it is necessary to investigate in detail the individual stages of downstream processing in order to obtain high product yields without loss of quality. After a survey of recovery operations and information on some special features of proteins which are relevant to downstream processing, this paper deals with the methods of precipitation, chromatography and foam fractionation. Several results obtained with a real, multicomponent system, namely the supernatant of lipase fermentation, are presented and compared with one another.     

Miscibility of bacterial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with ester substituted celluloses

Summary Blends of bacterial Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with cellulose acetate butyrate (CAB) and cellulose acetate propionate (CAP) were prepared by melt blending. When CAB or CAP content in the blends is 50%, the blends are stable, homogeneous mixed glasses, characterized by a glass transition that follows the Fox equation. When the cellulose ester content is lower than 50%, PHBV crystallizes upon room storage and the blends are partially crystalline. Besides the strongly composition dependent glass transition, another slightly composition dependent relaxation is observed by both DMTA and DSC measurements in the vicinity of the glass transition of PHBV. It is suggested that both blend components partake in both mobilization processes.     

Miscible blends containing bacterial poly(3‐hydroxyvalerate) and poly(p‐vinyl phenol)

The miscibility of poly(3‐hydroxyvalerate) (PHV)/poly(p‐vinyl phenol) (PVPh) blends has been studied by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The blends are miscible as shown by the existence of a single glass transition temperature (T_g) and a depression of the equilibrium melting temperature of PHV in each blend. The interaction parameter was found to be −1.2 based on the analysis of melting point depression data using the Nishi–Wang equation. Hydrogen‐bonding interactions exist between the carbonyl groups of PHV and the hydroxyl groups of PVPh as evidenced by FTIR spectra. The crystallization of PHV is significantly hindered by the addition of PVPh. The addition of 50 wt % PVPh can totally prevent PHV from cold crystallization. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 383–388, 1999     

Strength development in powder processing of poly(tetrafluoroethylene)

Poly(tetrafluoroethylene) (PTFE) is a versatile engineering plastic with excellent chemical and electrical resistance, a wide working temperature range, and a low coefficient of friction. PTFE is processed by the powder processing technique because of its high melt viscosity. The powder processing of polymers involves cold compaction of the polymeric powders, followed by sintering of the preforms at elevated temperatures. Sintering is a critical operation since the mechanical properties of the products are determined by the interparticle coalescence and diffusion of polymer chains across the interface. The results of the studies of the strength development during sintering of PTFE are reported here. The strength was measured in terms of the tensile strength at break, and the dependence of the tensile strength on compaction pressure, particle size, and processing time is discussed. The time dependence of strength development could be described by a diffusion controlled process in which the strength is proportional to the 1/4th power of the processing time.     

Some recent developments in the processing of poly(vinyl chloride)

Poly(Vinyl chloride) is the basic material for a huge number of products which are fabricated using very many different techniques. Established processing techniques continue to be improved, leading to additional benefits in process efficiency and product quality. New processes are also being introduced which are intended to increase the efficiency of material usage and to open up new application areas. These include: molecular orientation, foaming, and cross-linking. Developments are also occurring in the use of PVC in conjunction with other materials as micro- or macro-composites. Processing techniques include coextrusion and lamination. Many processing methods are likely to benefit from the microelectronics revolution in process control and monitoring.     

CAST工艺在处理果汁加工废水中的应用

介绍了运用循环式活性污泥法（CAST）工艺处理果汁加工废水的工程实例。经过该工艺处理后．出水水质达到《辽宁省沿海地区污水直接排人海域标准》（DB21-59-1989）中一级标准,运行结果表明该工艺具有抗冲击负荷,运行稳定及污染物去除效果好等特点。     

Surface modification of poly(ethylene) in an rf downstream remote plasma reactor

Polyethylene (PE) was treated in a remote downstream reactor with oxygen, nitrogen, hydrogen, and mixed gas plasma. The effects of these treatments were investigated by contact angle goniometry and x-ray photoelectron spectroscopy (XPS). The oxygen plasma treatment allowed a rapid and efficient hydrophilation of the PE, although the samples were placed far outside the main discharge region. In hydrogen plasma treatment, only a small amount of polar functional groups are formed, while the nitrogen plasma results in a surface similar to that in an oxygen plasma treatment. Thirteen percent of oxygen was found by XPS in these samples, while only 3% of nitrogen was present. The mixed oxygen/hydrogen plasma treatment revealed that 0.1% oxygen in the process gas produced a detectable degree of oxidation. By experiments with quenched atomic oxygen, the singlet molecular oxygen (O½Δ) was found to be the major reactive species in the surface reaction in our system. The role and the source of radiation in this reaction is discussed. © 1993 John Wiley & Sons, Inc.     

Thermal analysis of FeCl3-doped poly(3-butylthiophene) and poly(3-dodecylthiophene)

Summary For neutral and FeCl₃-doped poly(3-butylthiophene) (P3BT) and poly(3-dodecylthiophene) (P3DDT), conductivity measurement and thermal analysis are performed. Before doping, the glass transition temperatures (T_g) of the P3BT and P3DDT are 75.4°C and 5.6°C respectively. No melting transition of an ordered phase for P3BT is observed. But for P3DDT, the melting temperatures of ordered side chains and main chains are 56.1°C and 116.3°C respectively. Upon doping, the T_g 's shift upward to 150.5°C and 51.2°C for P3BT and P3DDT respectively and the two melting peaks of the ordered phases of P3DDT disappear. The dopant anions decompose in the range of about 150 to 230°C. The conductivities increase with increasing temperature and reach maxima at 135°C and 28°C and drop sharply in the range of 160–200°C and 130–170°C for P3BT and P3DDT respectively. This indicates that the thermal motion of the main chains would lead to a drop of conductivity due to thermal undoping, while the dopant decomposition would lead to a rapid loss of conductivity and an occurrence of crosslinking reaction.     

Synthesis and electrochemical characterization of soluble poly(p-phenylene vinylene) derivatives containing olefinic bonds at the side chain

A new kind of soluble poly(p-phenylenevinylene) (PPV) derivative containing free olefinic bonds at the side chain is prepared and studied by electrochemical measurement. The electrochemical investigations reveal that the free olefinic bonds in these polymers are electroactive; a new redox reaction occurs prior to the oxidation of PPV backbone in the cyclic voltammetry. The lower oxidation potential of the olefinic bonds hints that it is possible for these olefinic bonds to react with oxygen, which is desirable to remove the harmful oxygen in the light-emitting polymer devices. The merits and possibility of such polymers containing olefinic bonds in the fabrication of the light-emitting devices are discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2535–2539, 1999     

Effects of poly(methyl methacrylate-co-n-butyl acrylate) on the properties and processing behavior of poly(vinyl chloride)

Random copolymers of methyl methacrylate/n-butyl acrylate with a BA content of 0–50% and M?_v = 0.16–4.04 × 10⁶ were synthesized and evaluated as a processing aid (PA) for poly(vinyl chloride) (PVC). Their effects on the processability and properties of PVC were investigated with respect to the composition, molecular weight, and the amount of the copolymer added. It was found that the fusion rate of PVC could be improved (i) by increasing the amount of the copolymer used, (ii) by increasing the butyl acrylate content in the copolymer, and (iii) by lowering the molecular weight of the copolymer. The effect of molecular weight, composition, and amount of copolymer on the ultimate mechanical properties of PVC was investigated. The presence of copolymer did not affect the impact strength. However, the tensile strength and elongation at break were improved, particularly at high temperature (125°C). It was also found that the “plate out” phenomenon of PVC could be significantly reduced in the presence of the processing aid.     

Thermal analyses of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

Thermal analyses of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB–HV)], and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(HB–HHx)] were made with thermogravimetry and differential scanning calorimetry (DSC). In the thermal degradation of PHB, the onset of weight loss occurred at the temperature (°C) given by T_o = 0.75B + 311, where B represents the heating rate (°C/min). The temperature at which the weight-loss rate was at a maximum was T_p = 0.91B + 320, and the temperature at which degradation was completed was T_f = 1.00B + 325. In the thermal degradation of P(HB–HV) (70:30), T_o = 0.96B + 308, T_p = 0.99B + 320, and T_f = 1.09B + 325. In the thermal degradation of P(HB–HHx) (85:15), T_o = 1.11B + 305, T_p = 1.10B + 319, and T_f = 1.16B + 325. The derivative thermogravimetry curves of PHB, P(HB–HV), and P(HB–HHx) confirmed only one weight-loss step change. The incorporation of 30 mol % 3-hydroxyvalerate (HV) and 15 mol % 3-hydroxyhexanoate (HHx) components into the polyester increased the various thermal temperatures T_o, T_p, and T_f relative to those of PHB by 3–12°C (measured at B = 40°C/min). DSC measurements showed that the incorporation of HV and HHx decreased the melting temperature relative to that of PHB by 70°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 90–98, 2001     

Effect of processing additives on (bio)degradability of film-blown poly(ε-caprolactone)

Poly(ε-caprolactone)s (PCL) with slip masterbatch, Erucamide, SiO₂ and Erucamide + CaCO₃ as low-molecular-weight processing additives, were film-blown in a single screw extruder. The films and recycled PCL without additives were exposed to composting, anaerobic sewage sludge (37 and 55°C), pure fungal culture, and chemical hydrolysis at two pH (7 and 10.5) and at two temperatures (room temperature and 50°C). Recycling and addition of processing additives resulted in a slightly slower degradation rate compared with the degradation of pure PCL. The degradations in biotic environment were generally faster than in abiotic environment. Higher degradation rates are observed in more complex environments (composts and anerobic sewage sludge) due to synergism between high temperature and a richer fauna of microorganisms. In the biotic environments, faster reductions in number-average molecular weight (M _n) than in weight-average molecular weight (M _w) were observed. A decrease of M _n with up to 75–80% was estimated for composted pure PCL, while similar samples in anaerobic sludge at 55°C were completely degraded in 50 days. The mechanical properties of the samples subjected to composting exhibited a more rapid enbrittlement compared to the samples subjected to abiotic hydrolysis. The observed increase in crystallinity with increasing degree of degradation is explained by crystallization made possible by chain cleavage in the amorphous phase. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 61–74, 1998     

Adsorption and electrosorption of mercury(II) acetate onto activated charcoal cloth from aqueous solution

The adsorption of mercury(II) acetate from aqueous solution onto an activated charcoal cloth (ACC) has been studied using shaking and flow-through techniques. It was found that the adsorption capacities of the ACC shaken in mercury(II) acetate solution could reach 2 × 10⁻³ mol g⁻¹ at pH 5.5. The flow-through experiments gave lower adsorption results because of a decreased concentration gradient and limitations due to film diffusion. The latter could be overcome by increasing the flow-rate. Application of an electrical potential to the ACC during flow-through experiments, increased the uptake of mercury(II). This was most marked when the applied polarity was negative, −1 volt, with respect to a Calomel reference electrode. Then the diffusion coefficient reached a constant value and the cloth continued to remove mercury(II) out of the solutions passing through it.     

Some properties of poly(3-hydroxybutyrate)–poly(3-hydroxyvalerate) blends

The melting, crystallization and dynamic mechanical behaviour of blends of bacterially produced poly[D (–)-3-hydroxybutyrate] (PHB) and poly[D (–)-3-hydroxyvalerate] (PHV) have been investigated. Results showed that melt-pressed PHB–PHV blends contained phase-separated domains in the melt which subsequently crystallized as PHB and PHV type spherulites respectively. The two melting regions detected by DTA related to separate melting of PHB and PHV crystallites, which were almost unaffected by the blend composition. The mechanical behaviour of a random copolymer of PHB/HV was compared with that of a blend of almost the same composition, and found to be markedly different.     

Production of Medium-Chain-Length Poly(3-hydroxyalkanoates) from Crude Fatty Acids Mixture by Pseudomonas putida

Microbial production of medium-chain-length poly(3-hydroxyalkanoates), PHA_MCL from crude fatty acids mixture was investigated. With ammonium as the growth limiting substrate, fatty acids mixture from saponified palm kernel oil (SPKO) supports good growth and PHA_MCL production of Pseudomonas putida PGA1. Growth of this microorganism on ammonium exhibited substrate inhibition kinetics which can be described using Andrews model with the substrate inhibition constant, K_i = 1.2 g L⁻¹. Concentration of SPKO in the aqueous medium should be at 10 g L⁻¹ or less, as higher concentrations can significantly reduced the volumetric oxygen transfer coefficient (K_La), biomass growth and PHA_MCL production. Uptake of SPKO by the organism follows a zero-order kinetics, indicating a mass transfer limitation of the free fatty acids by the P. putida PGA1 cells. In batch and fed-batch fermentations, PHA_MCL accumulation is encouraged under ammonium-limited condition with SPKO as the sole carbon and energy source. The amount of PHA_MCL accumulated and its specific production rate, q_PHA were influenced by the residual ammonium concentration level in the culture medium. It was observed that in both fermentation modes, when the residual ammonium becomes exhausted (<0.05 g L⁻¹), the PHA_MCL accumulation and q_PHA were significantly reduced. However, this effect can be reversed by feeding low amount of ammonium to the culture, resulting in significantly improved PHA_MCL yield and productivity. It is concluded that the feeding of residual ammonium concentration in the culture medium during the PHA_MCL accumulation has a positive effect on sustaining the PHA_MCL biosynthetic capability of the organism.