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.     

Characterization of polypropylene/layered silicate nanocomposites prepared by single-step method

The extent of organo-modified clay (C93A) platelets dispersion in polymer matrix and crystallization and melting behavior of iPP-based nanocomposites prepared by a single-step melt-mixing method were investigated by wide-angle X-ray diffraction (WAXD), transmission (TEM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). WAXD patterns revealed exfoliated structure of nanocomposites containing 1 wt% clay, and mixed intercalated/exfoliated structure at higher concentration of nanoclay. The isothermal crystallization proceeds faster in the matrix polymer (iPP/PP-g-MA) than in nanocomposite samples. The results obtained for T _m ^o suggest that the presence of nanoclay has induced a perfection of the formed crystals. The presence of C93A particles in PP leads to increase in crystallization peak temperature implying nucleating ability of clay particles, which was more pronounced in exfoliated than in mixed intercalated/exfoliated system.     

Melting behavior of a poly(ether‐block‐amide) copolymer melt‐crystallized under quiescent,isothermal conditions

Segmented poly(ether‐block‐amide) copolymers are typically known as polyamide‐based thermoplastic elastomers consisting of hard, crystallizable polyamide block and flexible, amorphous polyether block. The melting characteristics of a poly(ether‐block‐amide) copolymer melt‐crystallized under various quiescent, isothermal conditions were calorimetrically investigated using differential scanning calorimetry (DSC). For such crystallized copolymer samples, their crystalline structures under ambient condition and the structural evolutions upon heating from ambient to complete melting were characterized using ambient and variable‐temperature wide‐angle X‐ray diffractometry (WAXD), respectively. It was observed that dependent of specific crystallization conditions, the copolymer samples exhibited one, two, or three melting endotherms. The ambient WAXD results indicated that all melt‐crystallized copolymer samples only exhibited γ‐form crystals associated with the hexagonal habits of the polyamide homopolymer, whereas variable‐temperature WAXD data suggested that upon heating from ambient, a melt‐crystallized copolymer might exhibit so‐called Brill transition before complete melting. Based on various DSC and variable‐temperature WAXD experimental results obtained in this study, the applicability of different melting mechanisms that might be responsible for multiple melting characteristics of various crystallized PEBA copolymer samples were discussed. It was postulated that the low (T _m1) endotherm was primarily because of the disruption of less thermally stable, short‐range ordered structure of amorphous polyamide segments of the copolymer, which was only formed after the completion of primary crystallization via so‐called annealing effects. The intermediate (T_m2) and high (T_m3) endotherms were attributed to the melting of primary crystals within polyamide crystalline microdomains of the copolymer. The appearance of these two melting endotherms might be somehow complicated by thermally induced Brill transition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2035–2046, 2008     

New insights into the multiple melting behaviors of the semicrystalline ethylene‐hexene copolymer: Origins of quintuple melting peaks

A semicrystalline ethylene‐hexene copolymer (PEH) was subjected to a simple thermal treatment procedure as follows: the sample was isothermally crystallized at a certain isothermal crystallization temperature from melt, and then was quenched in liquid nitrogen. Quintuple melting peaks could be observed in heating scan of the sample by using differential scanning calorimeter (DSC). Particularly, an intriguing endothermic peak (termed as Peak 0) was found to locate at about 45 °C. The multiple melting behaviors for this semicrystalline ethylene‐hexene copolymer were investigated in details by using DSC. Wide‐angle X‐ray diffraction (WAXD) technique was applied to examine the crystal forms to provide complementary information for interpreting the multiple melting behaviors. Convincing results indicated that Peak 0 was due to the melting of crystals formed at room temperature from the much highly branched ethylene sequences. Direct heating scans from isothermal crystallization temperature (T_c, 104–118 °C) were examined for comparison, which indicated that the multiple melting behaviors depended on isothermal crystallization temperature and time. A triple melting behavior could be observed after a relatively short isothermal crystallization time at a low T_c (104–112 °C), which could be attributed to a combination of melting of two coexistent lamellar stack populations with different lamellar thicknesses and the melting‐recrystallization‐remelting (mrr) event. A dual melting behavior could be observed for isothermal crystallization with both a long enough time at a low T_c and a short or long time at an intermediate T_c (114 °C), which was ascribed to two different crystal populations. At a high T_c (116–118 °C), crystallizable ethylene sequences were so few that only one single broad melting peak could be observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2100–2115, 2008     

Crystallization of poly(N-methyldodecano-12-lactam) in blends with poly(styrene-stat-acrylic acid)

Crystallization behaviour of blends of poly(N-methyldodecano-12-lactam) (PMDL) with statistical copolymer poly(styrene-stat-acrylic acid) (PSAA) has been studied by the DSC and WAXD methods. The blend films prepared from dioxane solutions were crystallized at laboratory temperature for five days. Approximate crystallinities of as-prepared neat lower- PMDL 5 and higher-molecular weight PMDL 45 were 28% and 19%, respectively. With increasing PSAA content in the blends the crystallinities decreased sharply. The melting point of the primary crystalline structure of PMDL showed a decreasing dependence on PSAA content in the blends, confirming miscibility of the PMDL-PSAA pair. Recrystallization was strongly suppressed in the blends. The lower-melting endotherm appearing at about 10-15 °C above the crystallization temperature was attributed to melting to less perfect structures formed during secondary crystallization. In neat PMDL, the extent of secondary crystallization was approximately 5-10%. In the blends containing 20% PSAA approximate relative proportion of secondary crystallites on total crystallinity was 40% and 60% for the blends with PMDL 5 and PMDL 45, respectively. WAXD measurements did not reveal any change in crystal modification on blending. Increased T_g in blends of flexible PMDL cannot play a significant role in suppression of primary in favour of secondary crystallization. This was attributed to low mobility of PMDL chains due to dilution effect and specific interactions with the amorphous copolymer component, and, in case of the higher-molecular-weight PMDL, a greater involvement of entanglements. Higher T_g of blends was involved in retardation of non-isothermal crystallization on cooling and subsequent cold crystallization.     

The influence of wood flour and compatibilizer (<Emphasis Type="Italic">m</Emphasis>-TMI-<Emphasis Type="Italic">g</Emphasis>-PP) on crystallization and melting behavior of polypropylene

Wood flour/polypropylene composites (WPC) were prepared by melt extruding with different wood flour (WF) loadings. The non-isothermal crystallization and melting was studied with different WF loadings, for W40P60 and W40P60M6, the melting was investigated after non-isothermal and isothermal crystalline. Comparing with neat polypropylene, the melting behavior of the composites, both non-isothermally and isothermally, was investigated by differential scanning calorimetry (DSC). The results showed that WF was an effective heterogeneous nucleating agent, as evidenced by an increase in the crystallization temperature and the crystallinity for melt crystallization of PP with increasing WF content. For the non-isothermal samples, the origins of the double melting behaviors were discussed, based on the DSC results of PP. The XRD measurements confirmed that no crystalline transition existed during the non-isothermal crystallization process. With m-TMI-g-PP adding, due to compatibilization phenomenon were probably responsible for decreasing T _m, X _c. In the DSC scan after isothermal crystallization process, the single melting behaviors were found and each melting endotherm had a different origin.     

Study on melting and polymorphic behavior of poly(decamethylene terephthalamide)

This work describes the melting and polymorphic behavior of poly(decamethylene terephthalamide) (PA 10T). Both solution‐crystallized (SC) and melt‐crystallized (MC) PA 10T show double melting endotherms in DSC. The SC crystal form melts at 260–300°C giving the first melting endotherm, and meanwhile undergoes a polymorphic transition forming the MC crystal form. The subsequent melting of the MC crystal form gives the second melting endotherm at 300–325°C. This irreversible polymorphic transition is confirmed by variable‐temperature WAXD and IR. Dynamic mechanical thermal analysis (DMTA) shows a glass transition temperature (T_g) at 127°C and the presence of an α′ transition at 203°C (0.1 and 1 Hz). This transition could be confirmed by DSC and variable‐temperature WAXD experiments. The α′ transition correlates with a reversible thermal process and a sudden change in intersheet spacing. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 465–472     

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.     

Thermal properties of freezing bound water restrained by sodium lignosulfonate-based polyurethane hydrogels

In order to develop a new functional product from lignin, sodium lignosulfonate (LS)-based polyurethane (LSPU) hydrogels were prepared from LS and hexamethylene diisocyanate (HDI) derivatives in water. Isocyanate/hydroxyl group ratio (NCO/OH ratio) was varied from 0.05 to 0.8 mol mol⁻¹, and water content (W_c = mass of water/mass of dry sample) of the obtained LSPU hydrogels was varied from 0 to 3.0 g g⁻¹. Phase transition behavior of hydrogels with various W_c’s was investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). In DSC heating curve of LSPU hydrogels, glass transition, cold crystallization, melting and liquid crystallization were observed. Cold crystallization, two melting peaks and variation of melting enthalpy indicate that three kinds of water, i.e., non-freezing water, freezing bound water and free water, exist in LSPU hydrogel. Glass transition temperature (T_g) decreased from 230 to 190 K in a W_c range where non-freezing water was formed in the hydrogel. T_g increased when freezing bound water was formed in the system. T_g leveled off in a W_c range where normal ice was formed. The effect of NCO/OH ratio on molecular motion of LSPU hydrogel is examined based on T_g and heat capacity difference at T_g (ΔC_p). Water vaporization curve measured by TG also indicates the presence of bound water which evaporates at a temperature higher than ca. 410 K. By atomic force microscopic observation, the size of molecular bundle of LSPU hydrogel is calculated and compared with that of LS-water system. By cross-linking, the height of molecular bundle decreased from ca. 3–1 nm and lignin molecules extend in a flat structure.

     

MOLECULAR AND SUPRAMOLECULAR ORDERING IN CONFINED ENVIRONMENTS

Crystal and phase morphologies and structures determined by self-organization of crystalline-amorphous diblockcopolymers, crystallization of the crystallizable blocks, and vitrification of the amorphous blocks are reviewed through asystematic study on a series of poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymers. On the base ofcompetitions among these three processes, molecular and supramolecular ordering in confined environments can beinvestigated. In a concentration-fluctuation-induced disordered (D_(CF)) diblock copolymer, the competition between crystalli-zation of the PEO blocks and vitrification of the PS blocks is momtored by time-resolved simultaneous small angle X-rayscattering (SAXS) and wide angle X-ray diffraction (WAXD) techniques. In the case of T_c相似文献   

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.     

Solid-state relaxations in poly(ethylene oxide). I. Study using the differential scanning calorimetry method

Differential scanning calorimetry (DSC) studies show that poly(ethylene oxide) (PEO) exhibits three transition regions below its melting point. The effects of annealing on the intensity and temperature of these transitions enable us to locate T < T_g (T_γ) T_g, and T_α at about 130–140. 190–240, and 263–313°K, respectively. Our results argue for a small transition T_g (L) at 190–200°K with a second T_g (U) above 233°K, the temperature of which increases on annealing. The shape of DSC derivative curves reveals that T < T_g and T_α are complex and suggests the possibility of two steps in these processes. In addition, a splitting of T_α is observed every time a multiple melting endotherm appears as a result of annealing. Up to three separate melting endotherms can be observed. One of them is related to the normal primary crystallization process. Its peak temperature increases linearly with the annealing temperature, yielding an extrapolated value for the equilibrium melting temperature T of 347°K as found before.     

Crystallization behavior, thermal property and biodegradation of poly(3-hydroxybutyrate)/poly(ethylene glycol) grafting copolymer

The poly(3-hydroxybutyrate)(PHB)/poly(ethylene glycol)(PEG) grafting copolymer was successfully prepared by PHB and acrylate groups ended PEGM using AIBN as initiator. The crystallization behavior, thermal stability and environmental biodegradability of PHB/PEG grafting copolymers were investigated with differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and Biodegradation test in vitro. In the results, all the grafting copolymers were found to show the X-ray diffraction arising from the PHB crystal lattice, while none of the PEG crystallized peaks could be found even though the graft percent reached 20%. This result indicated that PEG molecules were randomly grafted onto PHB chain. The thermal properties measured by DSC showed that the melting temperature(T_m) and glass transition temperature (T_g) were both shifted to lower temperature with the graft percent increasing, and this broadened the narrow processability window of PHB. According to TGA results, the thermal stability of the grafting copolymers is not changed compared to pure PHB. From the biodegradation test, it could be concluded that degradation occurred gradually from the surface to the inside and that the degradation rate could be adjusted by the PEG grafting ratio. In another words, the biodegradation profiles of PHB/PEG grafting copolymer can be controlled. These properties make PHB/PEG grafting copolymer have promising potential applications especially in agriculture fields.     

Characterization,crystallization kinetics,and melting behavior of poly(ethylene succinate) copolyester containing 10 mol % butylene succinate

Copolyester was synthesized and characterized as having 89.9 mol % ethylene succinate units and 10.1 mol % butylene succinate units in a random sequence, as revealed by NMR. Isothermal crystallization kinetics was studied in the temperature range (T_c) from 30 to 73 °C using differential scanning calorimetry (DSC). The melting behavior after isothermal crystallization was investigated using DSC by varying the T_c, the heating rate and the crystallization time. DSC curves showed triple melting peaks. The melting behavior indicates that the upper melting peaks are associated primarily with the melting of lamellar crystals with various stabilities. As the T_c increases, the contribution of recrystallization slowly decreases and finally disappears. A Hoffman‐Weeks linear plot gives an equilibrium melting temperature of 107.0 °C. The spherulite growth of this copolyester from 80 to 20 °C at a cooling rate of 2 or 4 °C/min was monitored and recorded using an optical microscope equipped with a CCD camera. Continuous growth rates between melting and glass transition temperatures can be obtained after curve‐fitting procedures. These data fit well with those data points measured in the isothermal experiments. These data were analyzed with the Hoffman and Lauritzen theory. A regime II → III transition was detected at around 52 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2431–2442, 2008     

Thermal analysis of poly(2-methylpentamethylene terephthalamide)

Poly(2-methylpentamethylene terephthalamide) (Nylon M5T) is a new high temperature aromatic polyamide developed by Hoechst Celanese. In this paper thermal properties of Nylon M5T chips, as well as as-spun and drawn fibers were studied by DSC, DMA, hot stage microscopy and WAXS.T _g of the fully amorphous Nylon M5T is 143°C when measured by DSC;T _g increases with crystallinity to 151°C. The temperature dependence of the solid and melt specific heat capacities has also been determined. The heat capacity increase at the glass transition of the amorphous polymer is 103.9 J °C^–1 mol^–1.T _g by DMA for the as-spun fiber is 155°C, for a drawn fiber is 180°C. Three secondary transitions were observed by DMA in addition to the glass transition. These correspond to a local mode relaxation of the methylene groups at –120°C, onset of rotation of the amide-groups at –65°C and the onset of the rotation of the phenylenegroups (at 63°C). The crystallinity of Nylon M5T strongly depends on the rate of cooling from the melt. The isothermal crystallization data are melt temperature dependent: two-dimensional crystallization takes place when the samples are crystallized from higher melt temperatures, and this phase changes into a spherulitic structure during cooling to room temperature. Spherulitic crystallization occurs when lower melt temperatures are used. This polymer has three crystal forms as indicated by DSC, DMA and WAXS data. The crystal to crystal transitions are clearly visible when amorphous samples are heated in the DSC, or the DMA curves of as-spun fibers are recorded. It is experimentally shown that a considerable melting of the lower temperature crystal forms takes place during the crystal to crystal transitions. The equilibrium melting point as measured by the Hoffman-Weeks method, has been determined to be 339°C.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthday     

Thermal analysis of the double-melting behavior of poly(L-lactic acid)

The melting and crystallization behavior of poly(L -lactic acid) (PLLA; weight-average molecular weight = 3 × 10⁵) was studied with differential scanning calorimetry (DSC). DSC curves for PLLA samples were obtained at various cooling rates (CRs) from the melt (210 °C). The peak crystallization temperature and the exothermic heat of crystallization determined from the DSC curve decreased almost linearly with increasing log(CR). DSC melting curves for the melt-crystallized samples were obtained at various heating rates (HRs). The double-melting behavior was confirmed by the double endothermic peaks, a high-temperature peak (H) and a low-temperature peak (L), that appeared in the DSC curves at slow HRs for the samples prepared with a slow CR. Peak L increased with increasing HR, whereas peak H decreased. The peak melting temperatures of L and H [T_m(L) and T_m(H)] decreased linearly with log(HR). The appearance region of the double-melting peaks (L and H) was illustrated in a CR–HR map. Peak L decreased with increasing CR, whereas peak H increased. T_m(L) and T_m(H) decreased almost linearly with log(CR). The characteristics of the crystallization and double-melting behavior were explained by the slow rates of crystallization and recrystallization, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 25–32, 2004     

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     

Ringed spherulites in ternary polymer blends of poly(<Emphasis Type="Italic">ε</Emphasis>-caprolactone), poly(styrene-<Emphasis Type="Italic">co</Emphasis>-acrylonitrile), and polymethacrylate

The relationship between ringed spherulite morphology, crystallization regimes/kinetics, and molecular interactions in miscible ternary blends of poly(-caprolactone) (PCL), poly(benzyl methacrylate) (PBzMA), and poly(styrene-co-acrylonitrile) (SAN) was investigated by using differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). The interactions resulted in the deviation of both experimental and calculated T_gs and formation of the specific morphology of the spherulitic structure. Ring-banded spherulites were observed in the PCL/PBzMA/SAN ternary blends. The width of ring bands changed with the blend ratio and the crystallization temperature. Additionally, both composition and wt% of AN in the SAN copolymer had an apparent effect on the morphology of PCL spherulites. Both the crystallization structure of lamellae and molecular interactions greatly influenced the ring bands of PCL spherulites. Furthermore, by using the Flory–Huggins approximation, the depression of the melting point showed that interactions in the PCL/PBzMA/SAN-17 blend were greater than in the PCL/PBzMA/SAN-25 blend. In the ternary blends, the great molecular interactions between amorphous and crystalline polymer resulted in better homogeneity and a larger band period of the extinction rings in the PCL spherulites.     

Crystallization, morphology, and dynamic mechanical properties of poly(trimethylene terephthalate)/clay nanocomposites

The poly(trimethylene terephthalate) (PTT)/clay nanocomposite has been successfully prepared via melt intercalation using a co-rotating twin screw extruder. The nanocomposite was characterized by wide angle X-ray diffraction (WAXD), transmission electron microscope (TEM), differential scanning calorimetry (DSC), polarized light microscope (PLM) and dynamic mechanical analysis (DMA). The nanocomposite forms an exfoliated structure, which can be observed by WAXD and TEM. The effect of clay layers on the crystallization behaviors of PTT was studied through isothermal and non-isothermal crystallization methods. The results suggest that the introduction of nanosize clay layers accelerates the crystallization rate of PTT and the clay layers act as nucleation agents. The morphology of spherulites was investigated with PLM and the result is well in agreement with crystallization kinetics. DMA shows that glass transition temperature (T_g) and storage modulus (E^′) of the PTT matrix of the nanocomposite are higher than those of pure PTT.