Catalyzed chain extension of poly(butylene adipate) and poly(butylene succinate) with 2,2′‐(1,4‐phenylene)‐bis(2‐oxazoline)

Low‐molecular‐weight HOOC‐terminated poly(butylene adipate) prepolymer (PrePBA) and poly(butylene succinate) prepolymer (PrePBS) were synthesized through melt‐condensation polymerization from adipic acid or succinic acid with butanediol. The catalyzed chain extension of these prepolymers was carried out at 180–220°C with 2,2′‐(1,4‐phenylene)‐bis(2‐oxazoline) as a chain extender and p‐toluenesulfonic acid (p‐TSA) as a catalyst. Higher molecular weight polyesters were obtained from the catalyzed chain extension than from the noncatalyzed one. However, an improperly high amount of p‐TSA and a high temperature caused branching or a crosslinking reaction. Under optimal conditions, chain‐extended poly(butylene adipate) (PBA) with a number‐average molecular weight up to 29,600 and poly(butylene succinate) (PBS) with an intrinsic viscosity of 0.82 dL/g were synthesized. The chain‐extended polyesters were characterized by IR spectroscopy, ¹H‐NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis, wide‐angle X‐ray scattering, and tensile testing. DSC, wide‐angle X‐ray scattering, and thermogravimetric analysis characterization showed that the chain‐extended PBA and PBS had lower melting temperatures and crystallinities and slower crystallization rates and were less thermally stable than PrePBA and PrePBS. This deterioration of their properties was not harmful enough to impair their thermal processing properties and should not prevent them from being used as biodegradable thermoplastics. The tensile strength of the chain‐extended PBS was about 31.05 MPa. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crystallization behavior of partially crosslinked poly(β‐hydroxyalkonates)/poly(butylene succinate) blends

Partially crosslinked poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate)/poly(butylene succinate) (PHBV/PBS) and poly(β‐hydroxybutyrate)/poly(butylene succinate) (PHB/PBS) blends were prepared by melt compounding with dicumyl peroxide. The effect of partial crosslinking on crystallization of the PHBV/PBS and PHB/PBS blends was investigated systematically. Differential scanning calorimetry results showed that the overall crystallization rates of both PHBV and PBS in their blends were enhanced considerably by the partial crosslinking. Similar results were also detected in the PHB/PBS blends. The polarized optical microscope observation displayed that the nuclei density of PHBV was increased while the spherulitic morphology did not change much. Conversely, the PBS spherulites turned into cloud‐like morphology after the partial crosslinking which is a result of the decrease in spherulite size, the reduction in interspherulite distance and the interconnection of fine PBS domains. Wide angle X‐ray diffraction patterns confirmed the enhancement in crystallization of the PHBV/PBS blends after the partial crosslinking without modification on crystalline forms of the PHBV and PBS components. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41020.     

Thermal properties and degradation behavior of poly(1,4‐butylene adipate)/modified layered double hydroxide nanocomposites

In this study, poly(1,4‐butylene adipate) (PBA)/organomodified layered double hydroxide (m‐LDH) nanocomposites were synthesized and characterized as a new material for green materials use. m‐LDH was initially prepared with magnesium nitrate hexahydrate, aluminum nitrate‐9‐hydrate, oleic acid, and sorbitol by a novel one‐step coprecipitation method to intercalate the oleic acid and sorbitol organomodifier into the interlayer of the layered double hydroxide. The solution mixing process was then applied and shown to be an efficient method for fabricating the PBA/m‐LDH nanocomposites. The m‐LDH characterized by X‐ray diffraction (XRD) showed a high interlayer spacing of 58.8 Å. The morphology and thermal properties of the PBA/m‐LDH nanocomposites were characterized with XRD, transmission electron microscopy, and thermogravimetric analysis. It was shown that the m‐LDH was well distributed in the PBA matrix and that the thermal properties of the PBA/m‐LDH nanocomposites significantly improved with a loading of 0.1 wt % m‐LDH. Finally, the biodegradability of the PBA/m‐LDH nanocomposites was tested with lipase from Pseudomonas fluorescens as a microbial catalyst. It was shown that an addition of m‐LDH up to 0.5% resulted in a significant difference in terms of the biodegradability. After 120 h of degradation, the residual weight and surface morphology of the composite films were affected by the presence of m‐LDH. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42083.     

Effect of nucleating agents on the crystallization behavior and heat resistance of poly(l‐lactide)

Poly (l ‐lactide) (PLLA) blends with various nucleators were prepared by melt processing. The effect of different nucleators on the crystallization behavior and heat resistance as well as thermomechanical properties of PLLA was studied systematically by differential scanning calorimetry, X‐ray diffraction, heat deflection temperature tester, and dynamic mechanical analysis. It was found that poly(d ‐lactide), talcum powder (Talc), a multiamide compound (TMC‐328, abbreviated as TMC) can significantly improve the crystallization rate and crystallinity of PLLA, thus improving thermal–resistant property. The heat deflection temperature of nucleated PLLA can be as high as 150°C. The storage modulus of nucleated PLLA is higher than that of PLLA at the temperature above T_g of PLLA. Compared with other nucleating agents, TMC was much more efficient at enhancing the crystallization of PLLA and the PLLA containing TMC showed the best heat resistance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42999.     

Crystallization kinetics of bacterial poly(3‐hydroxylbutyrate) copolyesters with cyanuric acid as a nucleating agent

Effects of cyanuric acid (CA) on nonisothermal and isothermal crystallization, melting behavior, and spherulitic morphology of bacterial copolyesters of poly(3‐hydroxybutyrate), i.e., poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBH), have been investigated. CA has excellent acceleration effectiveness on the melt crystallization of bacterial PHB, PHBV, and PHBH, better than the nucleating agents reported in the literatures, such as boron nitride, uracil, and orotic acid. PHBV and PHBH do not crystallize upon cooling from the melt at 10°C/min, while they are able to complete crystallization under the same conditions with an addition of 1% CA, with a presence of sharp crystallization exotherm at 75–95°C. Isothermal crystallization kinetics of neat and CA‐containing PHBV and PHBH were analyzed by Avrami model. Crystallization half‐times (t_1/2) of PHBV and PHBH decrease dramatically with an addition of CA. The melting behavior of isothermally melt‐crystallized PHBV and PHBH is almost not influenced by CA. Spherulitic numbers of PHBV and PHBH increase and the spherulite sizes reduce with an incorporation of CA. Nucleation densities of PHBV and PHBH increase by 3–4 orders of magnitude with a presence of 1% CA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Biodegradable poly(L‐lactic acid)/poly(butylene succinate‐co‐adipate) blends: Miscibility,morphology, and thermal behavior

Blends of two biodegradable and semicrystalline polymers, poly(L ‐lactic acid) (PLLA) and poly(butylene succinate‐co‐adipate) (PBSA), were prepared by solvent casting in different compositions. The miscibility, morphology, and thermal behavior of the blends were investigated using differential scanning calorimetry and optical microscopy. PLLA was found to be immiscible with PBSA as evidenced by two independent glass transitions and biphasic melt. Nonisothermal crystallization measurements showed that fractionated crystallization behavior occurred when PBSA was dispersed as droplets, evidenced by multiple crystallization peaks at different supercooling levels. Crystallization and morphology of the blends were also investigated through two‐step isothermal crystallization. For blends where PLLA was the major component, different content of PBSA did not make a significant difference in the crystallization mechanism and rate of PLLA. For blends where PBSA was the major component, the crystallization rate of PBSA decreased with increasing PLLA content, while the crystallization mechanism did not change. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Crystallization behavior and morphology of poly(lactic acid) with a novel nucleating agent

To improve the crystallization ability of poly(lactic acid) (PLA), a novel nucleating agent with a benzoyl hydrazine compound was used in this study. The crystallization behaviors of PLA/talc and PLA/bibenzoylhydrazinepropane (BBP) with or without poly(ethylene glycol) (PEG) were investigated with differential scanning calorimetry (DSC) and polarized optical microscopy. The DSC curves showed that the crystallization temperature and crystallinity of PLA/BBP (PBBP) was higher than that of PLA/talc. With the addition of PEG, a synergistic effect was found. According to the results of nonisothermal crystallization kinetics, the values of F(T) of PBBP_0.5PEG₅ were usually smaller than those of PTa₃PEG₅, so the nucleation efficiency of BBP was much better than that of talc. From a polarized optical microscopy photo, it was easy to determine that the nucleation density of BBP was higher than that of PTa₃PEG₅, and the spherulitic diameter increased linearly with the crystallization time no matter the impingements. The spherulitic growth rate of PBBP_0.5PEG₅ was faster than that of PTa₃PEG₅, and the induction time of PBBP_0.5PEG₅ was the shortest among all of the samples. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41367.     

Radiation‐induced crosslinking and mechanical properties of blends of poly(lactic acid) and poly(butylene terephthalate‐co‐adipate)

Blends of poly(L ‐lactic acid) (PLLA) and poly (butylene terephthalate‐co‐adipate) (PBTA) were prepared at ratios of 50 : 50, 60 : 40, and 80 : 20 by melt blending in a Laboplastomill. Improved mechanical properties were observed in PLLA when it was blended with PBTA, a biodegradable flexible polymer. Irradiation of these blends with an electron beam (EB) in the presence of triallyl isocyanurate (TAIC), a polyfunctional monomer, did not cause any significant improvement in the mechanical properties, although the gel fraction increased with the TAIC level and dose level. Irradiation of the blends without TAIC led to a reduction in the elongation at break (E_b) but did not show a significant effect on the tensile strength. E_b of PBTA was unaffected by EB radiation in the absence of TAIC. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization behavior of poly(ϵ‐caprolactone)/graphite oxide composites

A series of poly(?‐caprolactone) (PCL)/graphite oxide (GO) composites were synthesized through the ring‐opening polymerization of ?‐caprolactone with GO as an initiator. The crystallization behavior of the PCL–GO composites and the effects of the PCL–GO composites as nucleation agents on the crystallization behavior of PCL were also studied. The introduction of GO as PCL–GO composites shortened the crystallization half‐time for both the isothermal crystallization and nonisothermal crystallization of PCL, and this clearly indicated that GO in the PCL–GO composites had a great nucleating effect on the crystallization of pure PCL. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Crystallization behavior of fully biodegradable poly(lactic acid)/poly(butylene adipate‐co‐terephthalate) blends

Both poly(lactic acid) (PLA) and poly(butylene adipate‐co‐terephthalate) (PBAT) are fully biodegradable polyesters. The disadvantages of poor mechanical properties of PLA limit its wide application. Fully biodegradable polymer blends were prepared by blending PLA with PBAT. Crystallization behavior of neat and blended PLA was investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and wide angle X‐ray diffraction (WAXD). Experiment results indicated that in comparison with neat PLA, the degree of crystallinity of PLA in various blends all markedly was increased, and the crystallization mechanism almost did not change. The equilibrium melting point of PLA initially decreased with the increase of PBAT content and then increased when PBAT content in the blends was 60 wt % compared to neat PLA. In the case of the isothermal crystallization of neat PLA and its blends at the temperature range of 123–142°C, neat PLA and its blends exhibited bell shape curves for the growth rates, and the maximum crystallization rate of neat PLA and its blends all depended on crystallization temperature and their component. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Biodegradable poly(butylene succinate‐co‐butylene adipate)/multiwalled carbon nanotube nanocomposites: Preparation,morphology, and crystallization behavior

Biodegradable poly(butylene succinate‐co‐butylene adipate) (PBSA)/multiwalled carbon nanotubes (MWCNTs) nanocomposites were prepared via a simple melt‐compounding method at low MWCNTs contents. Scanning and transmission electron microscopy observations revealed a relatively nice dispersion of MWCNTs throughout the PBSA matrix. Both the nonisothermal and isothermal melt crystallizations of PBSA were enhanced significantly in the nanocomposites relative to neat PBSA because of the presence of MWCNTs; however, the crystal structure of PBSA remained unchanged. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Crystallization and melting behavior of poly(ε‐caprolactone‐co‐δ‐valerolactone) and poly(ε‐caprolactone‐co‐L‐lactide) copolymers with novel chain microstructures

Nuclear magnetic resonance spectroscopy (NMR) characterization of the statistical copolymers of this study showed that the poly(ε‐caprolactone‐co‐L‐lactide)s, with ε‐caprolactone (ε‐CL) molar contents ranging from 70 to 94% and ε‐CL average sequence length (l_CL) between 2.20–9.52, and the poly(ε‐caprolactone‐co‐δ‐valerolactone)s, with 60 to 85% of ε‐CL and l_CL between 2.65–6.08, present semi‐alternating (R→2) and random (R～1) distribution of sequences, respectively. These syntheses were carried out with the aim of reducing the crystallinity of poly(ε‐caprolactone) (PCL), needed to provide mechanical strength to the material but also responsible for its slow degradation rate. However, this was not achieved in the case of the ε‐caprolactone‐co‐δ‐valerolactone (ε‐CL‐co‐δ‐VAL). Non‐isothermal cooling treatments at different rates and isothermal crystallizations (at 5, 10, 21 and 37°C) were conducted by differential scanning calorimetry (DSC), and demonstrated that ε‐CL copolymers containing δ‐valerolactone (δ‐VAL) exhibited a larger crystallization capability than those of L‐lactide (L‐LA) and also arranged into crystalline structures over shorter times. The crystallization enthalpies of the ε‐CL‐co‐δ‐VAL copolymers during the cooling treatments and their heat of fusion (ΔH_m) at the different isothermal temperatures were very large (i.e. ΔH_c > 53 Jg^?1) and in some cases, unrelated to the copolymer composition. In some compositions, such as the 60 : 40, Wide Angle X‐ray Scattering (WAXS) proved that that these two lactones undergo isomorphism and co‐crystallize in a single cell. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42534.     

Biodegradable composites of poly(butylene succinate‐co‐butylene adipate) reinforced by poly(lactic acid) fibers

Biodegradable composites of poly(butylene succinate‐co‐butylene adipate) (PBSA) reinforced by poly(lactic acid) (PLA) fibers were developed by hot compression and characterized by Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analyzer, and tensile testing. The results show that PBSA and PLA are immiscible, but their interface can be improved by processing conditions. In particular, their interface and the resulting mechanical properties strongly depend on processing temperature. When the temperature is below 120 °C, the bound between PBSA and PLA fiber is weak, which results in lower tensile modulus and strength. When the processing temperature is higher (greater than 160 °C), the relaxation of polymer chain destroyed the molecular orientation microstructure of the PLA fiber, which results in weakening mechanical properties of the fiber then weakening reinforcement function. Both tensile modulus and strength of the composites increased significantly, in particular for the materials reinforced by long fiber. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43530.     

Poly(styrene‐co‐maleic anhydride) ionomers as nucleating agent on the crystallization behavior of poly(ethylene terephthalate)

Poly(styrene‐co‐maleic anhydride) (SMA) ionomers were synthesized and designed as a new kind of nucleation agent according to the crystallization theory for improving the crystallization of poly(ethylene terephthalate) (PET). The crystallization behavior of PET with the addition of nucleation agents was investigated by differential scanning calorimetry, polarized‐light microscope, and X‐ray diffraction (XRD). Avrami equation and Hoffman–Lauritzen theory are adopted for analyzing isothermal and non‐isothermal crystallization kinetics, respectively. The results show that the addition of 1 wt % SMA ionomers effectively accelerates the crystallization rate and reduces the fold surface free energy of PET at high temperature regions. PLM results also indicated that the crystals impinge on each other, thus decreasing the spherulite size for PET/SMA ionomers samples compared with PET. XRD measurement revealed that the introduction of SMA ionomers does not change the crystal structure but indeed accelerates the crystallinity of PET. The results clearly demonstrate that our synthesized SMA ionomers are an efficient nucleating agent for PET. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41240.     

Crystallization kinetics of poly(butylene terephthalate) and its talc composites

Crystallization kinetics of poly (butylene terephthalate) (non‐talc‐PBT) and its 0.1 wt % talc composites (talc‐PBT) was determined for a wide range of cooling rates and isothermal temperatures. The critical cooling rate to suppress crystallization is 2000 K s^?1 for non‐talc‐PBT and 7000 K s^?1 for talc‐PBT. The cooling rate dependence of the total enthalpy change and heating rate dependence of enthalpy of cold crystallization are quantitatively discussed on the basis of the Ozawa's method. For isothermal crystallization, the annealing‐temperature (T _iso) dependence of crystallization half‐time (t _1/2) shows a bimodal curve with two minima. Talc shortens the t _1/2 at T _iso above 340 K and acts as a heterogeneous nucleation agent. Tammann's approach revealed that the t _1/2 is shortened by pre‐nucleation for non‐talc‐PBT but not for talc‐PBT. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44739.     

Biodegradable poly(ethylene succinate) blends and copolymers containing minor amounts of poly(butylene succinate)

Poly(ethylene succinate) (PES), poly(butylene succinate) (PBS), and PES‐rich copolyesters were synthesized using an effective catalyst, titanium tetraisopropoxide. PES was blended with minor amounts of PBS for the comparison. The compositions of the copolyesters and the blends were determined from NMR spectra. Their thermal properties were studied using a differential scanning calorimeter (DSC), a temperature modulated DSC (TMDSC), and a thermogravimetric analyzer. No significant difference exists among the thermal stabilities of these polyesters and blends. For the blends, the reversible curves of TMDSC showed a distinct glass‐rubber transition temperature (T_g), however, the variation of the T_g values with the blend compositions was small. Isothermal crystallization kinetics and the melting behavior after crystallization were examined using DSC. Wide‐angle X‐ray diffractograms (WAXD) were obtained for the isothermally crystallized specimens. The results of DSC and WAXD indicate that the blends have a higher degree of crystallinity and a higher melting temperature than those of the corresponding copolymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of lignin particles as a nucleating agent on crystallization of poly(3‐hydroxybutyrate)

The effect of lignin fine powder, as a new kind of nucleating agent, on the crystallization process of poly(3‐hydroxybutyrate) (PHB) was studied. The kinetics of both isothermal and nonisothermal crystallization processes from the melt for both pure PHB and PHB/lignin blend was studied by means of differential scanning calorimetry. Lignin shortened the crystallization half‐time t_1/2 for isothermal crystallization. The activation energy ΔE for PHB/lignin and pure PHB in the isothermal crystallization process was ?237.40 and ?131.22 kJ/mol, respectively, clearly indicating that the crystallization of the PHB/lignin blend was more favorable than that of pure PHB from a thermodynamic perspective. At the same time, according to polarized optical microscopy, the rate of spherulitic growth from the melt increased with the addition of lignin, which is ascribed to the reduction of surface fold energy σ_e, that is, σ_e is 59.2 × 10^?3 and 41.6 × 10^?3 J m^?2 for pure PHB and PHB/lignin, respectively. Polarized optical microscopy also showed that the spherulites found in PHB with lignin were smaller in size and greater in number than those found in pure PHB. The wide‐angle X‐ray diffraction indicated that an addition of lignin caused no change in the crystal structure and degree of crystallinity. These results indicated that lignin is a good nucleating agent for the crystallization of PHB. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2466–2474, 2004     

Crystallization behavior and viscoelasticity of bamboo‐fiber composites

This article deals with the effect of the kneading temperature on the crystallization of a matrix polymer and the viscoelasticity of a bamboo‐fiber‐reinforced biodegradable polymer composite. Upon the investigation of poly(butylene succinate) after melt mixing, spherulite generation was observed with polarized light microscopy and differential scanning calorimetry measurements. An increase in the spherulite dimensions was observed at high kneading temperatures (>150°C) in both the neat polymer and the bamboo‐fiber composite. Spherulite growth was initiated from the bulk matrix polymer and not from the surface of the bamboo fibers. The kneading temperature influenced the melt viscoelasticity above the melting point of poly(butylene succinate) but did not influence the viscoelasticity below the melting point. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 603–612, 2005     

Crystallization behavior of α‐cellulose short‐fiber reinforced poly(lactic acid) composites

The isothermal crystallization behavior of α‐cellulose short‐fiber reinforced poly(lactic acid) composites (PLA/α‐cellulose) was examined using a differential scanning calorimeter and a petrographic microscope. Incorporating a natural micro‐sized cellulose filler increased the spherulite growth rate of the PLA from 3.35 μm/min for neat PLA at 105°C to a maximum of 5.52 μm/min for the 4 wt % PLA/α‐cellulose composite at 105°C. In addition, the inclusion of α‐cellulose significantly increased the crystallinities of the PLA/α‐cellulose composites. The crystallinities for the PLA/α‐cellulose composites that crystallized at 125°C were 48–58%, higher than that of the neat PLA for ～13.5–37.2%. The Avrami exponent n values for the neat and PLA/α‐cellulose composites ranged from 2.50 to 2.81 and from 2.45 to 3.44, respectively, and the crystallization rates K of the PLA/α‐cellulose composites were higher than those of the neat PLA. The activation energies of crystallization for the PLA/α‐cellulose composites were higher than that of the neat PLA. The inclusion of α‐cellulose imparted more nucleating sites to the PLA polymer. Therefore, it was necessary to release additional energy and initiate molecular deposition. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of the melting temperature on the crystallization behavior of a poly(l‐lactide)/poly(d‐lactide) equimolar mixture

The effect of the final melting temperature (T_f) on the crystallization of poly(l ‐lactide) (PLLA)/poly(d ‐lactide) (PDLA) was studied via a combination of differential scanning calorimetry, wide‐angle X‐ray scattering, polarized optical microscopy, and Fourier transform infrared (FTIR) spectroscopy. We observed that a residual stereocomplex (SC) crystal induced the formation of SC crystals during cooling from a T_f (230°C) just above the melting peak of the SC crystals. On cooling from a T_f (240°C) just above the endset temperature of SC crystal melting [T_m(S)(E)], the possible order structure and the strong interchain interaction promoted the preferential crystallization of SC crystals; this enhanced the formation of α crystals. During cooling from a T_f (≥250°C) far above T_m(S)(E), the crystallization peaks of α and SC crystals converged. The FTIR results indicated that the residual SC crystals, possible ordered structure, and interchain interactions in the melt might have been the key factors for the different crystallization of PLLA/PDLA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43015.