Thermal properties and applications of low molecular weight polyhydroxybutyrate

The properties of the low molecular weight polyhydroxybutyrate (LMWPHB) and LMWPHB plasticized polyhydroxybutyrate (PHB) are studied using differential scanning calorimetry (DSC), thermogravimetric analysis, wide-angle X-ray diffraction (WAXD), polarized optical microscope (POM), mechanical, and biodegradation tests. The results of DSC, WAXD, and POM indicate that LMWPHB has a lower glass transition temperature (T _g), crystallinity, crystallization rate, melting temperature (T _m), and crystal size than PHB due to its much smaller molecular weight. The tensile strength, T _g, T _m, crystallinity, crystallization rate, and thermal stability of LMWPHB plasticized PHB decrease, while the flexibility and biodegradation rate increase with the increasing content of the added LMWPHB. It is confirmed that LMWPHB can be used to improve the brittleness and control the biodegradation rate of PHB.     

Calorimetric study of Diepoxide Chain-Extended Poly(Ethylene Terephthalate)

A series of chain-extended PET samples were obtained by the use of different amounts of a diepoxide as chain extender, which was prepared for this purpose. These samples exhibited different intrinsic viscosities and degrees of branching or cross-linking. The effects of this differentiation on the thermal properties were studied by differential scanning calorimetry. The thermal parameters studied were the glass transition temperature (T_g), the cold-crystallization temperature (T_cc), the melting temperature (T_m), the enthalpy (ΔH_m) and the degree of crystallinity. The data revealed that, the higher the quantity of chain extender or the chain extension time, the higher T_gand T_cc, but the lower T_mand ΔH_m, i.e. the more amorphous the chain-extended samples, as also shown by density measurements. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal properties of poly(lactic acid)/organo-montmorillonite nanocomposites

Poly(lactic acid)/organo-montmorillonite nanocomposites were prepared by melt intercalation technique. Maleic anhydride-grafted ethylene propylene rubber (EPMgMA) was added into the PLA/OMMT in order to improve the compatibility and toughness of the nanocomposites. The samples were prepared by single screw extrusion followed by compression molding. The effect of OMMT and EPMgMA on the thermal properties of PLA was studied. The thermal properties of the PLA/OMMT nanocomposites have been investigated by using differential scanning calorimeter (DSC) and thermo-gravimetry analyzer (TG). The melting temperature (T _m), glass transition temperature (T _g), crystallization temperature (T _c), degree of crystallinity (χ_c), and thermal stability of the PLA/OMMT nanocomposites have been studied. It was found that the thermal properties of PLA were greatly influenced by the addition of OMMT and EPMgMA.     

Synthesis and characterization of wholly aromatic polyesters derived from 1-phenyl-2,6-naphthalene-dicarboxylic acid and aromatic diols

A series of new wholly aromatic polyesters was synthesized by melt polycondensation of 1-phenyl-2,6-naphthalenedicarboxylic acid (PNDA) and diacetates of various aromatic diols. The aromatic diols studied are hydroquinone (HQ), methylhydroquinone (MHQ), phenylhydroquinone (PHQ), (α-phenylisopropyl)hydroquinone (PIHQ), 2,6-naphthalenediol (2,6-ND), 1,4-naphthalenediol (1,4-ND), and 4,4′-biphenol (BP). These polyesters were characterized for their crystallinity, glass transition temperature (T_g), melting temperature (T_m), liquid crystallinity, and thermal stability. In general, crystallinity of the polyesters are very low and the T_g values of the polyesters range from 150 to 172°C depending on the structure of aromatic diols. All of the polymers formed nematic phases above their T_m or T_g. The polyesters derived from PHQ and PIHQ are soluble in chlorinated hydrocarbon solvents. The initial decomposition temperatures of the polyesters are above 400°C under N₂ atmosphere. © 1996 John Wiley & Sons, Inc.     

Studies on the thermal properties of caprolactam/long chain lactam copolymer

The thermal properties of caprolactam/long chain lactam copolymer were studied with a Perkin-Elmer DSC 7. The melting point (T _m), heat of fusion (δH _m), crystalline degree (X _c), crystallization temperature (T _c) and glass transition temperature (T _g) of the copolymers increase with decrease of the content of the log chain lactam. From the changes in the mechanical properties with corresponding changes in the thermal properties, it is clear that the copolymers are thermal plastic and elastic. In addition, it is found that the results at a heating rate of 10 deg·min^?1 are almost the same as that at 20 deg·min^?1 after thermal history is erased.     

Investigation of structural and thermal characteristics of PVDF/ZnO nanocomposites

The structural and thermal behavior of PVDF/ZnO nanocomposites have been investigated by employing scanning electron microscopy (SEM),TEM, DSC, powder X-ray diffraction (XRD), thermally stimulated discharge current (TSDC), and transient current techniques. SEM/TEM observation indicated the homogeneous dispersion of functionalized ZnO nanoparticles throughout PVDF matrix. DSC shows that the crystallinity is influenced by the presence of ZnO nanoparticles in the PVDF matrix because the filler acts as efficient nucleating agent to facilitate PVDF crystallization. DSC results indicated the enhancement of the glass transition temperature (T _g), melting temperature (T _m) and crystallization temperature (T _c) of nanocomposites compared to pristine PVDF. XRD shows that the full-width at half maximum decreases with increasing ZnO content, which is attributed to the improvement in crystallinity. The incorporation of ZnO nanoparticles influences the modification of polarization process in PVDF as observed by means of TSDC and transient current study.     

Glass transition and crystallization kinetics analysis of Sb–Se–Ge chalcogenide glasses

Differential thermal analysis (DTA) has been employed to investigate the effect of Ge addition on the glass transition behavior and crystallization kinetics of Sb₁₀Se_90?xGe_x (x = 0, 19, 21, 23, 25, 27) alloys. The three characteristic temperatures viz. glass transition (T _g), crystallization (T _c), and melting (T _m) have been determined and found to vary with the heating rates and Ge content. Thermal stability and glass forming tendency have been evaluated in terms of ΔT (= T _c ? T _g) and reduced glass transition temperature. The activation energies for glass transition and crystallization have been used to analyze the nucleation and growth process. The activation energy analysis also determines the suitability of alloys to be used in switching applications. Results have been interpreted in terms of bond energies and structural transformations in the investigated alloys.     

Synthesis and characterization of a series of wholly aromatic copolyesters containing 2‐(α‐phenylisopropyl)hydroquinone moiety

Two series of new wholly aromatic thermotropic copolyesters containing the 2‐(α‐phenylisopropyl)hydroquinone (PIHQ) moiety have been synthesized and their basic properties such as glass transition temperature (T_g), melting temperature (T_m), thermal stability, crystallinity, and liquid crystallinity were studied by differential scanning calorimetry (DSC), thermogravimetry (TG), and wide‐angle X‐ray diffractometry (WAXD) and on a polarizing microscope. The first series was prepared from acetylated PIHQ, terephthalic acid (TPA), and 2,6‐naphthalenedicarboxylic acid (NDA), and the second series from acetylated PIHQ, TPA, and 1,1′‐biphenyl‐4,4′‐dicarboxylic acid (BDA). The T_g values (152–168°C) of the two series are not much different, although the values for the first series appear slightly higher. The T_m values (287–378°C) and the degree of crystallinity of the first series are appreciably greater than those of the second series. Such differences can be explained by the geometric structure of NDA and BDA moieties. All of the present polyesters are thermotropic and nematic. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 881–889, 1999     

Synthesis and properties of thermoplastic propyl-etherified amylose

Amylose was etherified with 1-bromopropane in DMSO. The degree of substitution (DS) was varied by altering the feed ratio of 1-bromopropane. The structures of the products were characterized by IR and 1H-NMR spectroscopy. When the molar feed ratio of 1-bromopropane to hydroxyl groups of amylose was beyond 7.5, the hydroxyl groups were completely substituted with propyl ether groups. The etherified amylose with DS 1.9 showed a glass transition temperature (T_g), and that with DS 2.3 or 3.0 showed both T_g and melting temperature (T_m) (DS 3.0 means complete substitution). The etherification imparted melt processability and solubility in nonpolar organic solvent to amylose.     

Synthesis and characterization of functional l-lactic acid/citric acid oligomer

Oligomers of l-lactic acid and citric acid (PLCA) were synthesized by reacting lactic acid with citric acid in the presence of stannous chloride. The chemical compositions of these multicarboxylated oligomers were verified by FT-IR and ¹H-NMR spectroscopy. The thermal characteristics of the oligomers, such as glass transition temperature T_g, melting temperature T_m and melting enthalpy, were confirmed by DSC. The crystallinity of the oligomers were determined by DSC and WXRD. Meanwhile, the acid-base surface characteristics of PLCA have been determined by contact angle. The results implicated that these oligomers may be used to entrap the cospecies on PLLA surface in tissue engineering.     

Thermal and crystallization characteristics of poly(trimethylene terephthalate)/poly(ethylene naphthalate) blends

Poly(trimethylene terephthalate) (PTT)/poly(ethylene naphthalate) (PEN) blends were miscible in the amorphous state in all of the blend compositions studied, as evidenced by a single, composition-dependent glass transition temperature (T_g) observed for each blend composition. The variation in the T_g value with the blend composition was well predicted by the Gordon-Taylor equation, with the fitting parameter being 0.57. The cold-crystallization peak temperature decreased with increasing PTT content, while the melt-crystallization peak temperature decreased with increasing amount of the minor component. The subsequent melting behavior after both cold- and melt-crystallization exhibited melting point depression, in which the observed melting temperatures decreased with increasing amount of the minor component. During melt-crystallization, both components in the blends crystallized concurrently just to form their own crystals. The blend with 60% w/w of PTT exhibited the lowest total apparent degree of crystallinity.     

Investigation and characterization of PVA-g-AAc/Zol membranes for possible practical use in separation processes

Poly(vinyl alcohol) films were grafted with two monomers (acrylic acid and N-vinyl imidazole) using the gamma irradiation technique. The melting temperature (T_m) and glass transition temperature (T_g) of the grafted membranes were determined with respect to the grafting yield. The ability of these membranes to separate cobalt from nickel has been investigated. The diffusion of cobalt and nickel ions from the feed compartment to the receiver compartment depends on the grafting yield and the pH of the feed solution. Cobalt ions do not diffuse through the membrane when the pH of the feed solution is >4.5. Thus, the prepared membranes could be considered for the separation of cobalt ions from nickel ions. The temperature of thermal decomposition of pure PVA-g-AAc/Zol membrane, PVA-g-AAc/Zol membranes containing cobalt ions, and PVA-g-AAc/Zol membranes containing nickel ions are determined using TGA analyzer; it was shown that the presence of cobalt and nickel increases the decomposition temperature. Also the membranes bonded with cobalt ions are more stable than the membranes containing nickel ions.     

Effect of microstructure on hydrolytic degradation studies of poly (l-lactic acid) by FTIR spectroscopy and differential scanning calorimetry

Structural changes during thermally induced crystallization and alkaline hydrolysis of Poly(l-lactic acid) (PLLA) films were investigated using differential scanning calorimetry (DSC), FTIR spectroscopy, weight loss, HPLC and optical microscopy. It was shown that crystallinity (χ_c), glass transition temperature (T_g) and melting temperature (T_m) were found to be strongly annealing temperature (T_a) dependent. The FTIR study of PLLA films suggested that the bands at 921 and 956 cm⁻¹ could be used to monitor the structural changes of PLLA. An independent infrared spectroscopic method was developed for the first time to determine crystallinity of PLLA before degradation and it showed good qualitative correlation with DSC crystallinity. The higher crystallinity values determined by FTIR were attributed to the intermediate phase included in the IR crystallinity. Both the weight loss data and the percentage of lactic acid obtained by HPLC showed that the alkaline hydrolysis of PLLA films increased with increasing crystallinity. The DSC observation showed an increase in T_g and no significant change in T_m and heat of fusion, while IR showed an increase in IR crystallinity with increasing hydrolysis time. The increase in IR crystallinity and T_g with hydrolysis time suggested that degradation progressed from the edges of the crystalline lamellas without decreasing lamellar thickness, but increased the intermediate phase and the short-range order.     

Crystallization behaviors and morphology of biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

Crystallization behaviors and spherulitic morphology of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] with different 4-hydroxybutyrate (4HB) molar fraction were investigated by differential scanning calorimetry and polarized optical microscopy. Crystallization behaviors of P(3HB-co-4HB) are significantly affected by 4HB molar fraction. The melting temperature (T _m), glass transition temperature (T _g), and crystallinity (X _c) decrease with the increase of 4HB molar fraction. Banded spherulites are observed in poly (3-hydroxybutyrate) (PHB) and P(3HB-co-4HB) copolymers. The band spacing decreases with the increase of 4HB molar fraction. The morphology and growth rate of the spherulites strongly depend on 4HB molar fraction and the crystallization temperatures. The introduction of 4HB unit can inhibit the emergence of cracks in PHB spherulites.     

Analysis of packing factors of crystalline polymers in terms of the glass transition to melting temperature radio

An expression for the ratio of the glass transition temperature to the melting temperature, T _g/T _m, was derived with allowance for fluctuations of the packing factor in the amorphous state. This relationship made it possible to describe the actual range of variation in T _g/T _m depending on a change in the packing factor in the crystalline state k _{o, cr}. The proposed approach forms the basis for the method of determination of increments in the packing ratio k _{o, cr} and formulation of the principles of selection of experimental data for calculations. The glass transition temperatures in polyethylene depending on the type of unit cell were calculated.     

Morphological behaviour of poly(lactic acid) during hydrolytic degradation

The hydrolytic degradation and the morphological behaviour of a packaging grade of poly(lactic acid) (PLA) were characterized by a series of techniques. During the initial degradation process (stage 1) at a temperature near the glass transition temperature (T_g), the molecular weight of PLA decreased as degradation time increased following a bulk erosion mechanism while the crystallinity increased simultaneously, but no observable weight loss occurred at stage 1. Mainly α-form PLA crystal structure was formed for the crystalline PLA with a low content of d stereo-isomers, but the material displayed a lower regularity, smaller domain size, lower melting temperatures T_m and different motional dynamics as compared to the original PLA with a similar level of crystallinity achieved by annealing. The amorphous PLA with a higher amount of d stereo-isomers also yielded the α crystalline phase as well as stereo-complex crystals at stage 1. When the molecular weight and the crystallinity reached a stable level, PLA started erosion into the degrading aqueous medium. During this stage of degradation (stage 2), the crystalline structure in PLA residues was further modified and both pH and temperature influenced the modification. The degradation at stage 2 was likely to follow a surface erosion mechanism with lactic acid as the major product of the weight loss. Besides the crystallinity effect on the degradation, temperature also played a key role in determining the rate of PLA degradation in both stages. The process was very slow at temperatures below the T_g of PLA but the rate was greatly enhanced at temperatures above the T_g.     

Structural collapse of plant materials during freeze-drying

Structural collapse of plant materials, which affects quality of foods, was studied. Fresh and osmotically dehydrated plant materials were freeze-dried at several chamber pressures, to achieve initial sample temperatures that were below (?55?C), near (?45?C), or above (?28?C) their glass transition temperature (T _g=?45?C). Freeze-drying at ?55?C resulted in products retaining their original volume. When the initial sample temperature was increased aboveT _g, the resulting freeze-dried samples collapsed. When the initial sample temperature was increased above the temperature of ice melting (T′_m), the samples collapsed further.     

Study of poly(bisphenol A carbonate) relaxation kinetics at the glass transition temperature

In this work, the variations of the relaxation times are investigated above and below the glass transition temperature of a model amorphous polymer, the polycarbonate. Three different techniques (calorimetric, dielectric and thermostimulated currents) are used to achieve this goal. The relaxation time at the glass transition temperature was determined at the temperature dependence convergence of the relaxation times calculated with dynamic dielectric spectroscopy (DDS) for the liquid state and thermostimulated depolarisation currents (TSDC) for the vitreous state. We find a value of τ(T_g) = 110 s for PC samples. The knowledge of the temperature dependence, τ(T), and the value τ(T_g) enables to determine the glass-forming liquid fragility index, m. We find m = 178 ± 5.     

Thermal properties of bio flour-filled polypropylene bio-composites with different pozzolan contents

In this study, the thermal properties of bio-flour-filled, polypropylene (PP) bio-composites with different pozzolan contents were investigated. With increasing pozzolan content, the thermal stability, 5% mass loss temperature and derivative thermogravimetric curve (DTG_max) temperatures of the bio-composites slightly increased. The coefficient of thermal expansion (CTE) and thermal expansion of the bio-composites decreased as the pozzolan content increased. The glass transition temperature (T _g), melting temperature (T _m) and percentage of crystallinity (X _c) of the bio-composites were not significantly changed. The thermal stability, thermal expansion and X _c of the maleic anhydride-grafted PP (MAPP)-treated bio-composites were much higher than those of non-treated bio-composites at 1% pozzolan content due to enhanced interfacial adhesion. X-ray diffraction (XRD) analysis confirmed the crystallinity of pozzolan-added bio-composites. From these results, we concluded that the addition of pozzolan in the bio-composites was an effective method for enhancing the thermal stability and thermal expansion.     

Thermal analysis of sulfonated polymers tested as polymer electrolyte membrane for PEM fuel cells

An aromatic polymer, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was sulfonate with different sulfonation degrees (30, 50, and 75?% theoretical degree) to obtain an electrolytic polymer suitable as proton exchange membrane for fuel cells. Thermal behaviors of sulfonated PPO were tested by differential scanning calorimetry and thermogravimetry. The sulfonation degrees were correlated with glass transitions temperatures (T _g) and the percent of weight loss. One notices a good fitting between sulfonation degree and the percent of weight loss thanks splitting of sulfonic moieties but it is not the same for glass transition temperatures that have a random variation.