Physical Properties of the Biodegradable Polymer Compositions Containing Natural Polyesters and their Synthetic Analogues

The thermal, mechanical and thermo-mechanical properties of polymer compositions, containing synthetic biodegradable polymers i.e. polylacide (PLA) and aliphatic-aromatic copolyester (BTA), natural biopolyester n-PHB and its synthetic atactic analog (a-PHB) were investigated. Thermal properties of the polymer compositions were studied by means of DSC . The compositions of various polymer weight ratio were tested. Compositions containing BTA and n-PHB create polyphase systems, what was confirmed by DSC. In this case the two Tg and two Tm values were observed. Polymer compositions containing PLA and BTA showed different behaviours. At the BTA content up to 30 weight % only one Tg and one Tm were indicated. At the increase of the BTA content to 50% weight and above, the two Tg, and two Tm were observed. Mixtures of BTA with n-PHB, PLA and with a-PHB show considerably greater values of the strain (ε) in comparison with initial polymers (n-PHB, PLA). It was found that in contrary to mixtures containing PLA, at the BTA content in the mixture with n-PHB above 50% of weights increases not only the strain, but also the stress at break (σ). Strong increase of the ε value in PLA/a-PHB mixtures with the content of a-PHB above 30% of weights were observed.     

Optimization of Biodegradable Nanocomposites Based on aPLA/PCL Blends for Food Packaging Applications

Biodegradable blends of amorphous poly(lactic acid) (aPLA) and polycaprolactone (PCL) and nanocomposites of these blends were developed by melt blending. A morphological study of the bioblends was carried out by means of WAXS and SEM showing immiscible behavior. The nanocomposites were also characterized morphologically by WAXS, TEM and SEM, revealing high degree of interaction of the nanoclays with the aPLA. Mechanical, thermal and gas barrier properties of the different blends and nanocomposites were studied and the effect of blending and clay addition on the above-mentioned properties was evaluated.     

Physico-Mechanical Properties of Biodegradable Rubber Toughened Polymers

Summary: In this study, blends of poly(lactic acid) (PLA) with poly(butylene adipate-co-terephthalate) (PBAT) were studied for their mechanical and thermal properties as a function of the PBAT content. Tensile testing, impact testing, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMTA) and scanning electron microscopy (SEM) were used to characterize the blends. It was observed that PLA/PBAT blends maintained quite high modulus and tensile strength compared to pure PLA. Small amounts of PBAT improved the elongation at break and the impact resistance showing a debonding effect typical of rubber toughened systems.     

Miscibility and Mechanical Behavior of SAN/NBR Blends

Summary: Aiming the development of high toughness polymer materials, blends of poly(styrene-co-acrylonitrile) (SAN) and poly(butadiene-co-acrylonitrile) (NBR) rubbers, with contents of acrylonitrile (AN) varying from 21 to 45%, were prepared by casting, coprecipitation and monoscrew extrusion followed by injection molding. SAN/NBR blends, prepared in the compositions (w/w) 90/10, 80/20, 70/30, 60/40, and 50/50, were characterized by differential scanning calorimetry (DSC) and Izod impact tests. DSC analyses showed that blends with 33% AN NBR prepared by casting, and with 39% AN NBR prepared by coprecipitation, are partially miscible at 60/40, 70/30 and 80/20 (SAN/NBR) compositions and immiscible for 50/50 compositions. On the other hand, 90/10 SAN/NBR systems were totally miscible. The blends with 45% AN NBR prepared by coprecipitation showed partial miscibility to 50/50, 60/40, 70/30 and 90/10 compositions and total miscibility to 80/20 composition. The NBR addition results in a significant increase in the impact resistance, strongly dependent on the blend composition and the NBR AN content. The best result of impact resistance — 75.2 ± 8.6 (kJ · m⁻²) — was obtained for SAN/NBR 50/50, using 45% AN NBR. This value is 15.7 times bigger than that for pure SAN -4.8 ± 0.7 (kJ · m⁻²).     

Synchrotron SAXS and WAXS Studies on Changes in Structural and Thermal Properties of Poly[(R)‐3‐hydroxybutyrate] Single Crystals during Heating

Summary: The annealing and melting behavior of poly[(R)‐3‐hydroxybutyrate] (P(3HB)) single crystals were followed in real time by synchrotron small‐ (SAXS) and wide‐angle X‐ray scattering (WAXS) measurements. The real‐time SAXS measurements revealed that the P(3HB) single crystal exhibits a discontinuous increase of lamellar thickness during heating. The structural changes as observed by SAXS and WAXS were in response to the thermal properties of single crystals characterized by differential scanning calorimetry.

A series of two‐dimensional small‐angle X‐ray scattering patterns of P(3HB) single crystal mats during the lamellar thickening process.     

A SAXS and swelling study of cured natural rubber/styrene–butadiene rubber blends

A small‐angle X‐ray scattering (SAXS) and swelling study of natural rubber and styrene–butadiene rubber blends (NR/SBR) is presented. To this aim, specimens of NR and SBR and blends with 75/25, 50/50, and 25/75 NR/SBR ratios (in phr) were prepared at a cure temperature of 433 K and the optimum cure time (t₁₀₀). This time was obtained from rheometer torque curves. The system of cure used in the samples was sulfur/n‐t‐butyl‐2‐benzothiazole sulfenamide. From swelling tests of the cured samples, information about the molecular weight of the network chain between chemical crosslinks was obtained. For all cured compounds, in the Lorentz plots built from SAXS scattering curves, a maximum of the scattering vector q around 0.14 Å^?1 was observed. However, the q position shows a linear‐like shift toward lower values when the SBR content in the SBR/NR blend increases. In pure NR or SBR the q values show a different tendency. The results obtained are discussed in terms of the existence of different levels of vulcanization for each single phase forming the blend and the existence of a third level of vulcanization located in the interfacial NR/SBR layer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2320–2327, 2009     

用SAXS/WAXS研究聚氧乙烯/聚氧丁烯嵌段共聚物在n-己烷中的结晶性球形胶束结构

嵌段共聚物在选择性溶剂中能够自组装形成胶束,胶束的不同形状与嵌段共聚物的结构、溶剂和浓度有关．无定形嵌段共聚物通常形成球形胶束,在某些情况下也可以形成其它形状的胶束,关于结晶性嵌段共聚物在无定形链段选择性溶剂中的胶束结构和形状的报道非常少．由于结晶和相似相溶两种作用力的竞争,使得这类胶束的形状丰富多变．通常结晶作用较强时,结晶性嵌段共聚物形成片状的胶束,当结晶组分比较少时,可形成棒状胶束,尽管理论上已经指出存在球形胶束,但尚无关于这方面的报道。     

Novel Biodegradable and Thermosensitive Dex‐AI/PNIPAAm Hydrogel

The dextran‐allyl isocyanate/poly(N‐isopropylacrylamide) (Dex‐AI/PNIPAAm) hydrogel was designed and prepared by copolymerization of the modified dextran with N‐isopropylacrylamide (NIPAAm). This novel Dex‐AI/PNIPAAm hydrogel is biodegradable and intelligent due to its biodegradable dextran linkage and thermosensitive PNIPAAm moiety. With an increase in dextran content, it exhibits the increased lower critical solution temperature (LCST) and decreased porous microstructure. Also, the thermosensitivity of this hydrogel is also controllable and adjustable depending on the different compositions.

SEM micrographs of the Dex‐AI/PNIPAAm hydrogels.     

Effect of Polydispersity on the Phase Behavior of Polymer Blends

Summary: The effect of polydispersity on polymer blend phase behavior is studied by in situ small‐angle X‐ray scattering. In a polydisperse polyethylene (PE)/isotactic poly(propylene) (iPP) blend, the enthalpic portion of the interaction parameter is greater than that of a corresponding blend with lower polydispersity. This is attributed to the presence of long chains, which provide a higher interaction energy and packing constraint, reducing the system miscibility. As expected, the radius of gyration is higher in the system with higher polydispersity.

Comparison of phase diagrams of the iPP/PE system used in this study (thin lines) with that obtained from the literature (thick lines). The solid lines represent binodals and the dashed lines are spinodals.     

Thermal Degradation of Poly(Vinyl Chloride)/Polyaniline Conducting Blends

A series of blends of poly(vinyl chloride) (PVC) and polyaniline (PANI) was prepared by solution casting and investigated by methods of thermal analysis, namely thermogravimetric analysis (TG), coupled with Fourier transform infrared spectroscopy (TG-FT/IR) and differential scanning calorimetry (DSC). It was found that the thermal stability of this polymer system depends on the composition of blend; the main product of prevailing PVC decomposition process — hydrogen chloride — seems to play specific role during degradation since it can react with PANI structures, characterized by different protonation degree. This revised version was published online in August 2006 with corrections to the Cover Date.     

含无规共聚物三元共混体系SMMA-PMMA-SAN相行为

含无规共聚物共混体系的相容性研究正在成为近年来的研究热点 ,因为相容的驱动力来自共聚物分子内不同单体链段间的排斥性相互作用 [1～ 3] .目前研究这类体系还主要采用过份简化的 F- H平均场理论 ,用旨在克服平均场理论缺陷的 Flory状态方程 ( EOS)理论仅局限于研究二元共聚物共混体系[4～ 8] .与三元共混体系相比 ,用 EOS理论预测含两个无规共聚物三元体系相行为尚需确定共聚物 -共聚物间的二元参数 sj/si,Xij和 Qij.若用 Ax B1- x和 Cy D1- y分别代表共聚物 1和 2 ,则 A,B,C,D代表相应共聚物中的单体单元 ,x,y分别是 1和 2的共…     

Infrared Spectroscopy and X-Ray Diffraction Studies on the Structure and Thermal Behavior of Biodegradable Polyhydroxyalkanoates

The structure and thermal behavior of new types of bacterial copolyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); P(HB-co-HHx) (HHx=2.5, 3.4, and 12 mol %) have been explored by means of wide-angle x-ray diffraction (WAXD), differential scanning calorimetry (DSC), and infrared (IR) spectroscopy. The WAXD pattern of P(HB-co-HHx) (HHx=12 mol %) copolymer measured at room temperature has revealed that it has an orthorhombic system (α=β=γ=90°) with a=5.76Å, b=13.20Å, c=5.96Å (fiber repeat), which is identical to that of poly(3-hydroxybutyrate) (PHB). It has been found from the temperature-dependent variations of the WAXD pattern that only the a lattice parameter shows the thermal expansion, while the b lattice parameter changes little with temperature in the crystalline P(HB-co-HHx) (HHx=12 mol %). This observation suggests that there are inter and intramolecular interactions between C=O groups and alkyl groups along the a axis and that interactions are broken little by little with temperature. IR spectra were measured for the four kinds of polymers over a temperature range from 30°C to high temperatures (200°C; PHB, 180°C; P(HB-co-HHx) (HHx=2.5 mol %), 180°C; P(HB-co-HHx) (HHx=3.4 mol %), 150°C; P(HB-co-HHx) (HHx=12 mol %)). Temperature-dependent IR spectral variations were analyzed for the CH, C=O, and C-O-C stretching band regions, and bands characteristic of crystalline and amorphous parts were identified in each region. It has been found from the IR study that the strength of interaction between the C=O group and the CH₃ (or CH₂) group is similar among the four polymers and that the population of C=O groups that are not involved in the interaction becomes higher with the increase in HHx. Both WAXD and IR studies have revealed that the crystallinity of P(HB-co-HHx) (HHx=12 mol %) decreases gradually starting from relatively low temperature (about 60°C) while that of PHB remains high up to 170°C.     

SIMULTANEOUS SAXS／WAXS／DSC STUDIES ON MICROSTRUCTURE OF CONVENTIONAL AND METALLOCENE-BASED ETHYLENE-BUTENE COPOLYMERS

The fractions of one metallocene-based (mPE) and one conventional (znPE) ethylene-butene copolymer eluted at 80-82℃ from temperature rising elution fractionation were selected for DSC and time-resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) characterization. The DSC and WAXS results show that two crystal structures exist in both mPE and znPE: structure A with higher melting temperature and structure B with lower melting temperature. It was found that original znPE (s-znPE) contains more highly ordered structure A than original mPE (s-mPE) in spite of the higher comonomer content of znPE. Another structure C is also identified because of higher crystallinity measured by WAXS than by DSC and is attributed to the interfacial region. The SAXS data were analyzed with correlation function and two maxima were observed in s-mPE and s-znPE, in agreement with the conclusion of two crystal populations drawn from DSC and WAXS results. These two crystal populatiorts have close long periods in s-mPE, but very different long periods in s-znPE. In contrast, freshly crystallized mPE and znPE (f-mPE and f-znPE) contain only a single crystal population with a broader distribution of long period     

Miscibility in crystalline/amorphous blends of poly(3-hydroxybutyrate)/DGEBA

A differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) study of miscibility in blends of the semicrystalline polyester poly(3-hydroxybutyrate) (PHB) and amorphous monomer epoxy DGEBA (diglycidyl ether of bisphenol A) was performed. Evidence of the miscibility of PHB/DGEBA in the molten state was found from a DSC study of the dependence of glass transition temperature (T_g) as a function of the blend composition and isothermal crystallization, analyzing the melting point (T_m) as a function of blend composition. A negative value of Flory–Huggins interaction parameter χ_PD was obtained. Furthermore, the lamellar crystallinity in the blend was studied by SAXS as a function of the PHB content. Evidence of the segregation of the amorphous material out of the lamellar structure was obtained. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Mechanical and Morphological Properties of Bio-Phenolic/Epoxy Polymer Blends

Polymer blends is a well-established and suitable method to produced new polymeric materials as compared to synthesis of a new polymer. The combination of two different types of polymers will produce a new and unique material, which has the attribute of both polymers. The aim of this work is to analyze mechanical and morphological properties of bio-phenolic/epoxy polymer blends to find the best formulation for future study. Bio-phenolic/epoxy polymer blends were fabricated using the hand lay-up method at different loading of bio-phenolic (5 wt%, 10 wt%, 15 wt%, 20 wt%, and 25 wt%) in the epoxy matrix whereas neat bio-phenolic and epoxy samples were also fabricated for comparison. Results indicated that mechanical properties were improved for bio-phenolic/epoxy polymer blends compared to neat epoxy and phenolic. In addition, there is no sign of phase separation in polymer blends. The highest tensile, flexural, and impact strength was shown by P-20(biophenolic-20 wt% and Epoxy-80 wt%) whereas P-25 (biophenolic-25 wt% and Epoxy-75 wt%) has the highest tensile and flexural modulus. Based on the finding, it is concluded that P-20 shows better overall mechanical properties among the polymer blends. Based on this finding, the bio-phenolic/epoxy blend with 20 wt% will be used for further study on flax-reinforced bio-phenolic/epoxy polymer blends.     

Thermal and Morphological Studies on Poly(Methyl Methacrylate)/Thermoplastic Polyurethane Blends

Poly(methyl methacrylate) (PMMA) and thermoplastic polyurethane (TPU) blends in different compositions viz., 95/05, 90/10, 85/15 and 80/20 (by wt/wt% of PMMA/TPU) have been prepared by melt mixing using a twin screw extruder. The thermal stability of these blends has been characterized by thermogravimetric (TG) analysis. All the blends are stable up to 381°C and complete degradation occurs at 488°C. A slight improvement in thermal stability was noticed with an increase in TPU content in the blends. Surface morphology of the blends has been studied by an optical microscope. Optical microphotographs revealed two‐phase morphology for all the blends.