The fracture of poly(hydroxybutyrate)Part I Fracture mechanics study during ageing

Linear elastic fracture mechanics techniques have been used to study the fracture behaviour of the biodegradable thermoplastic poly(hydroxybutyrate). Both the compact tension and double cantilever beam test geometries have been used and give toughness values in good agreement. The variation in fracture toughness with age after moulding has been monitored. It has been found that the strain energy release rate is reduced during ageing, but the stress intensity factor is increased. The primary change during ageing is found to be in the polymers stiffness rather than its resistance to fracture. © 1998 Chapman & Hall     

A qualitative in vitro evaluation of the degradable materials poly(caprolactone), poly(hydroxybutyrate) and a poly(hydroxybutyrate)-(hydroxyvalerate) copolymer

A qualitative in vitro evaluation of poly(caprolactone) (PCL), poly(hydroxybutyrate) (PHB) and a poly(hydroxybutyrate)-(hydroxyvalerate) (PHB-PHV) copolymer was carried out using primary human osteoblasts (HOB) and a human osteosarcoma (HOS) cell line. The cells were grown on films of these polymers and cultured for 2 and 4 days with cells grown on Thermanox as a control. The cells on each of the polymers exhibited different cellular morphologies with different rates of cell proliferation. Results from a preliminary degradation study demonstrated that biodegradable materials can be partially degraded using enzymes such as papain and trypsin. Of the solutions tested, papain caused the greatest degradation, with phosphate-buffered saline (PBS) a physiological buffer having very little effect over a six week period. The bone cells were grown on partially degraded polymers and no differences in the performance of HOS and HOB cells on the materials were observed.     

The fracture of poly(hydroxybutyrate)Part II Fracture mechanics study after annealing

The fracture behaviour of poly(hydroxybutyrate) (PHB) after high-temperature annealing has been studied using linear elastic fracture mechanics techniques. The effect of the annealing temperature on the polymers' fracture toughness both initially and after re-ageing is examined. Annealing at temperatures of 120°C or above is found to result in an improvement in both the critical stress intensity factor and the strain energy release rate measurements of fracture toughness which is largely maintained on re-ageing. A more detailed study of the re-ageing behaviour after annealing at 130°C finds Gc to remain approximately constant but Kc to increase slightly with age. © 1998 Chapman & Hall     

Biocompatibility and biodegradation of poly(hydroxybutyrate)/poly(ethylene glycol) blend films

Using chloroform as co-solvent, a series of poly(3-hydroxybutyrate) (PHB) and polyethylene glycol (PEG) blend materials with different ratio ranging from 80 : 20 (wt %) to 20 : 80 (wt %) were prepared by solution blend. The blood-compatibility was evaluated by means of platelet clotting time test and exploring its morphological changes. The results showed that PEG played an important role in resisting platelet adhesion. With the increased addition of PEG, the clotting times became longer and the number of platelet adhesion decreased apparently. All platelets were in discrete state, no pseudopodium had been found and no collective phenomenon had been happened. The cell-compatibility was evaluated via Chinese Hamster Lung (CHL) fibroblast cultivation in vitro. The cells cultured on the matrix spread and proliferated well. With the increase of PEG content in the blend films, the number of live cells became more and more. These results indicated that PHB exhibited satisfying cell-compatibility and the addition of PEG also could improve the cell-compatibility of PHB. The biodegradation experiment indicated that the degradation of PHB/PEG was accelerated by enzyme in vitro and the blending of PEG was favorable to degradation.     

Short range ordering in amorphous In-Se films by wide-angle X-ray scattering

Wide-angle X-ray scattering studies were performed on In-Se amorphous films, obtained by thermal evaporation, with selenium content of 60 and 66 at.%. The intensities were recorded in the scattering vector range between 3 and 160 nm^–1. Structural information about the local structure of the amorphous In-Se films has been derived from the radial distribution function using the curve-fitting method. The experimental results have been compared with model based simulations. The obtained structural parameters indicate that for In₄₀Se₆₀ In-In, In-Se and Se-Se contributions are involved in the near-neighbour coordination sphere. As the Se content is increased, the number of In-In bonds is reduced to zero, within the precision of the method. For both amorphous films In is tetrahedrally coordinated while Se has three near neighbours on the average.     

Synchrotron radiation small-angle X-ray scattering study on fracture process of carbon nanotube/poly(ethylene terephthalate) composite films

Time-resolved small-angle X-ray scattering (SAXS) measurements have been conducted during tensile deformation of carbon nanotube (CNT)/amorphous poly(ethylene terephthalate) (PET) composite films using synchrotron radiation in order to investigate the fracture process. The observed SAXS patterns consisted of the streaks parallel to the loading direction caused by the total reflection at craze/polymer interfaces, the streaks perpendicular to the loading direction caused by the fibril/void structure of crazes and the scattering from CNTs. The formation, widening and fracture processes of the crazes were investigated based on the changes of SAXS patterns during deformation and the fracture toughness of the composite films determined with essential work of fracture method. The influences of CNT addition on the mechanical properties of PET varied depending on the specimen geometries used for the mechanical tests and marked influences were obtained with surface-notched specimens. The CNT addition increased the energy needed to widen the crazes and retarded the growth and fracture of the crazes during deformation. This lead to the increases in the plastic work of fracture and the fracture toughness of PET. The CNT aggregates formed at the CNT fraction beyond 3 wt%, however, caused reduction of the fracture toughness.     

Nucleation,growth and morphology of poly(hydroxybutyrate) and its copolymers

Measurements of the melting temperatures, growth rates and nucleation rates of meltcrystallized polyhydroxybutyrate (PHB) and two poly(hydroxybutyrate-co-hydroxyvalerate) (PHB/HV) copolymers are reported for crystallization over a wide range of temperature. Examples are shown of the spherulitic morphologies obtained. From the variation in melting point with crystallization temperature values for the equilibrium melting points of PHB and PHB/HV are obtained. Growth and nucleation rate measurements are analysed using secondary nucleation theory to obtain approximations to surface energies within the crystals. PHB and PHB/7% HV are described well by secondary nucleation theory. PHB/23% HV exhibits more complex crystallization and melting behaviour, which suggests temperature-dependent exclusion of HV units from the crystals.     

Composites of amorphous calcium phosphate and poly(hydroxybutyrate) and poly(hydroxybutyrate-co-hydroxyvalerate) for bone substitution: assessment of the biocompatibility

Composites of amorphous carbonated apatite and poly-(R)-3-hydroxybutyrate (PHB) and poly-(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate (PHBHV), respectively, were studied by pH monitoring upon immersion in water and by long-term osteoblast culture. For comparison, α-tricalcium phosphate (α-TCP), one glass ceramic (GB 9N), and one bioglass (Mg 5) were subjected to the same experiments. Excellent cell proliferation was found on the composite of calcium phosphate with PHB and on the reference materials (α-TCP, glass ceramic, bioglass). In contrast, cell death was observed repeatedly on the composite with PHBHV. A composite of amorphous calcium phosphate and PHB appears to be well suited as slowly biodegradable bone substitution material.No benefit of any kind will be received either directly or indirectly by the authors.W. Linhart and W. Lehmann contribute equally and therefore share first authorship     

A small-angle X-ray scattering study of aqueous solutions of uranium(IV) complexes with lacunar heteropolytungstates

The behavior of aqueous and acid solutions of U(IV) complexes with lacunar heteropolyanions was studied by small-angle X-ray scattering. The polytungstate forms in solutions and in crystals are generally similar. The polyanionic complexes in solutions can exhibit ordering with a period of approximately 5.6–7.8 nm. Such species are probably precursors of the crystalline form.     

Physical ageing studies in semicrystalline poly(ethylene terephthalate)

The physical ageing of semicrystalline poly(ethylene terephthalate) (c-PET) of different crystallinities and morphological structures was studied using differential scanning calorimetry. Samples of c-PET of crystallinity content _c = 0.12, crystallized at low temperatures (105 °C for 13 min), submitted to physical ageing in a temperature range between 50 and 65 °C for different periods of time, showed two endothermic peaks. The first peak (P₁) of higher intensity, appeared at a temperature close to the glass transition temperature, T _g, of the amorphous PET, and the other peak (P₂) of lower intensity, merged as a shoulder of the first one, at a higher temperature. These peaks have been attributed to the enthalpy relaxation process of two different amorphous regions: one amorphous phase outside the spherulitic structure (interspherulitic amorphous region) and another amorphous phase inside the spherulites (interlamellar amorphous region). The separation between P₁ and P₂ indicates that DSC, via enthalpy relaxation, is a good technique to detect the real double glass transition of the semicrystalline PET. However, the physical ageing of a semicrystalline PET of _c = 0.32, crystallized at 114 °C during 1 h, showed a main endothermic peak shifted to a higher temperature, which probably corresponds to the enthalpy relaxation of the more restricted interlamellar amorphous region, and a small endothermic peak at lower temperature which could be a reflection of the hindered interspherulitic amorphous region.     

聚3-己基噻吩的光电性能研究

利用光电化学方法研究了聚3-己基噻吩的光电化学性质,其禁带宽度为1.89eV,同时确定了它的价带位置(-3.6eV)、导带位置(-5.4eV).研究发现聚3-己基噻吩属于直接跃迁型半导体,在本文条件下得到的最高IPCE值达5.2%     

Morphology of single crystals of poly (hydroxybutyrate) and copolymers of hydroxybuty rate and hydroxyvalerate

Single crystals of poly(hydroxybutyrate), and copolymers of hydroxybutyrate and hydroxyvalerate, have been grown from a variety of solvents and their morphology studied. In all cases the crystals appear elongated, with the crystallographic a axis along the long axis of the crystals. Screw dislocations (which act as branch points and can lead to large crystal aggregates) have been observed, and solvents, e.g. octanol in which more of these dislocations occur, have been identified. Decoration of the crystals with polyethylene shows that the fold plane is the (0 1 0) plane, while crystallographic and crystallinity arguments require successive adjacent folds to be along 1 1 0 directions. It is argued that folding is along [1 1 0] on the top, and [1 ¯1 0] on the bottom surface of a crystal.     

Soft X-ray image storage in poly (methylmethacrylate)

Images stored in resist for soft X-ray lithography or microradiography were found to show a background noise which limits the resolution. This is due to the statistically variable spatial distribution of the photons incident on the resist surface. An estimate of the fundamental noise-limited resolution has been made from the experimental measurement of photon flux incident on the surface and the accurate development rate curves. Monochromatic radiation from a synchrotron source was used.     

Change of mechanical properties of rigid poly(vinylchloride) during photochemical ageing

Thermally stabilised, unpigmented, rigid PVC samples, were exposed to accelerated photoageing at 40°C, 55°C and 70°C. The concentration profiles of photoproducts were determined on microtome slices ( 20 m) parallel to the irradiated surface using IR (carbonyls) and UV (polyenic double bonds) spectrophotometry and by steric exclusion chromatography (Mn and Mw). They indicate that carbonyls and chain scissions predominate only in a thin superficial layer whereas polyconjugated double bonds and crosslinks predominate in a subcutaneous layer (300–400 m). Tensile measurements show that the ultimate elongation decreases after an induction period whose duration is a decreasing function of temperature. The change of mechanical behaviour can be described in terms of a ductile-brittle transition shift mechanism in which crosslinking plays an important role. A tentative explanation of a such crosslinking induced transition is proposed in the discussion.     

The fracture of poly(hydroxybutyrate) Part III Fracture morphology in thin films and bulk systems

This paper is the final part of a three paper series describing the fracture and ageing behaviour of poly(hydroxybutyrate). In the first two parts conventional fracture mechanics methods were used to monitor changes both during the detrimental room temperature ageing process that occurs and after a subsequent annealing process that had been reported to reverse the ageing process. This paper reports on our studies of the morphology of fracture surfaces and how fracture proceeds in different ways in the original, ductile, fresh, material, the more brittle, aged material and the ductile, annealed material. We have used optical and electron microscopic techniques to examine fracture surfaces of samples which had already been well characterised by mechanical testing. The effect of ageing and high temperature annealing on the resultant fracture morphology is detailed for both thin films and bulk samples. We have found that PHB undergoes crazing before failure regardless of annealing history. We have studied the craze morphology using optical microscopy and scanning electron microscopy. Both aged and un-aged samples are found to deform in approximately the same manner, the primary difference on ageing being the volume of material that is plastically deformed. After high temperature annealing a different craze morphology has been observed. In thin films this is characterised by the formation of a dense zone of micro-crazes over a relatively large area. In bulk samples there is a distinct change in the resultant fracture surface. In both thin films and bulk systems there is an increased occurrence of fracture initiation in the spherulite cores after high temperature annealing which helps to extend the craze zone.     

A MALDI-TOF MS study of oligomeric poly(m-phenyleneisophthalamide)

MALDI-TOF MS was used to study the end-group distribution of a series of poly(m-phenyleneisophthalamide) oligomers which were synthesized using various mole percent ratios of diamine to diacid chloride (90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80, and 10:90) to clarify results obtained in previous work published in this journal. Oligomers synthesized with excess diamine or excess diacid chloride were found to contain abundances of amine or carboxylate end groups, respectively, as expected. Oligomers synthesized with equal molar ratios of reactants produced cyclic species which were also found in a previous publication as an oligomer in commercially produced, high molecular mass Nomex.     

壳聚糖/聚乳酸/聚羟基丁酸酯人工硬脑膜的制备与性能研究

以壳聚糖、聚乳酸、聚(R)-3-羟基丁酸甲酯等为主要成膜物质,用流延法制得新型薄膜材料。研究表明,当壳聚糖∶明胶∶聚乳酸为1∶1∶1时,得到膜的抗拉强度比其他的可生物降解膜都大,达到27.346MPa;当壳聚糖∶明胶∶聚(R)-3-羟基丁酸甲酯为1∶1∶1时,其抗拉强度达到24.363Mpa,防漏性能达到80h。经模拟体内降解研究,在人工脑脊液的环境中浸置44d后,降解率分别为20%左右,降解速度较慢,可以保持其结构6～7周,有利于引导组织再生材料的基本要求。因此该复合膜有望成为医用可生物降解人工硬脑膜。     

High strength and high modulus poly(vinyl alcohol) by the gel ageing method

The gel ageing method was proposed for producing high strength and high modulus poly(vinyl alcohol) (PVA) materials. The PVA gel prepared from a solution in a mixed solvent of dimethylsulfoxide water (v/v)=8020 at -34 °C was moulded into a gel sheet and then aged in water at 10 °C for several months. The gel sheet was dried and then drawn at 200 °C. The tensile strength and the modulus of the drawn film were 2.8 and 72 GPa, respectively. These excellent properties are discussed in relation to the structures of the aged gel, the dried gel (namely the film) and the drawn film using the results from X-ray diffraction, differential scanning calorimetry and birefringence measurements. As a result, the most important process was shown to be the ageing process. If the crystallites with relatively low melting temperatures, which were called the B and C crystallites, were grown in the aged gel, the mechanical properties of the drawn film from it were as high as those described above. The orientation of the crystallites mildly caused during drying of the gel sheet was also shown to be a key structure which facilitated the high extension of the chain in the subsequent drawing process.     

聚N-异丙基丙烯酰胺共聚物的动态光散射研究

以双键类单体N-异丙基丙烯酰胺(NIPAAm)、甲基丙烯酸(3-三甲氧基硅)丙酯(MPS)和甲基丙烯酸羟丙酯(HPMA)为原料,通过自由基聚合法制备了温敏性PNMH共聚物.利用动态光散射仪测试了共聚物在不同水溶液中的水力学直径,考查了温度、pH及盐类溶质对共聚物尺寸、构型及其最低临界溶液温度(LCST)的影响,同时分析...