Isothermal crystallization kinetics and spherulite morphologies of poly(lactic acid)/ethylene acrylate copolymer blends

Isothermal crystallization kinetics and spherulite morphologies of partially immiscible blends of poly(lactic acid) (PLA) and ethylene acrylate copolymer (EAC) were investigated by differential scanning calorimetry (DSC) and polarized optical microscopy. The DSC data obtained was analyzed using the Avrami equation. Crystallization kinetics of PLA from the melt was strongly influenced by the blend composition and the crystallization temperature. At a given crystallization temperature, the overall crystallization rate value was greater in the blends than in PLA suggesting that the presence of EAC enhanced crystallization of PLA. Polarized optical micrographs showed that the crystallization of PLA initially took place at the PLA/EAC interface. At high EAC content (>1 wt %), EAC domains acted as hindrance to crystallization reducing the overall crystallization rate of PLA in the blends. Based on the DSC analysis, the crystallization rate was maximum when PLA blend with 1 wt % EAC was isothermally crystallized at 103 °C. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45487.     

Poly(hydroxybutyrate)/poly(butylene succinate) blends: miscibility and nonisothermal crystallization

Four blends of poly(hydroxybutyrate) (PHB) and poly(butylene succinate) (PBSU), both biodegradable semicrystalline polyesters, were prepared with the ratio of PHB/PBSU ranging from 80/20 to 20/80 by co-dissolving the two polyesters in N,N-dimethylformamide and casting the mixture. Differential scanning calorimetry (DSC) and optical microscopy (OM) were used to probe the miscibility of PHB/PBSU blends. Experimental results indicated that PHB showed some limited miscibility with PBSU for PHB/PBSU 20/80 blend as evidenced by the small change in the glass transition temperature and the depression of the equilibrium melting point temperature of the high melting point component PHB. However, PHB showed immiscibility with PBSU for the other three blends as shown by the existence of unchanged composition independent glass transition temperature and the biphasic melt. Nonisothermal crystallization of PHB/PBSU blends was investigated by DSC using various cooling rates from 2.5 to 10 °C/min. During the nonisothermal crystallization, despite the cooling rates used two crystallization peak temperatures were found for PHB/PBSU 40/60 and 60/40 blends, corresponding to the crystallization of PHB and PBSU, respectively, whereas only one crystallization peak temperature was observed for PHB/PBSU 80/20 and 20/80 blends. However, it was found that after the nonisothermal crystallization the crystals of PHB and PBSU actually co-existed in PHB/PBSU 80/20 and 20/80 blends from the two melting endotherms observed in the subsequent DSC melting traces, corresponding to the melting of PHB and PBSU crystals, respectively. The subsequent melting behavior was also studied after the nonisothermal crystallization. In some cases, double melting behavior was found for both PHB and PBSU, which was influenced by the cooling rates used and the blend composition.     

聚乳酸/聚(已二酸-对苯二甲酸丁二酯)共混物的非等温结晶动力学

采用熔融挤出法制备了聚乳酸/聚(已二酸-对苯二甲酸丁二酯)共混物。利用差示扫描量热仪研究了聚乳酸及其共混体系的非等温结晶过程。用经Jeziorny修正的Avrami方程和Mo法对其非等温结晶动力学进行了分析。结果表明:Avrami方程和Mo法都适用于处理聚乳酸及其共混体系的非等温结晶过程,共混物的结晶速率大于聚乳酸的结晶速率。此外,用Huffman-Lauritzen理论计算了非等温结晶的结晶活化能,发现共混体系的结晶活化能绝对值小于聚乳酸。     

Crystallization of poly(3‐hydroxybutyrate) with stereocomplexed polylactide as biodegradable nucleation agent

Crystallization kinetics behavior and morphology of poly(3‐hydroxybutyrate) (PHB) blended with of 2–10 wt% loadings of poly(L ‐ and D ‐lactic acid) (PLLA and PDLA) stereocomplex crystallites, as biodegradable nucleating agents, were studied using differential scanning calorimetry, polarizing‐light optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). Blending PLLA with PDLA at 1:1 weight ratio led to formation of stereocomplexed PLA (sc‐PLA), which was incorporated as small crystalline nuclei into PHB for investigating melt‐crystallization kinetics. The Avrami equation was used to analyze the isothermal crystallization of PHB. The stereocomplexed crystallites acted as nucleation sites in blends and accelerated the crystallization rates of PHB by increasing the crystallization rate constant k and decreasing the half‐time (t_1/2). The PHB crystallization was nucleated most effectively with 10 wt% stereocomplexed crystallites, as evidenced byPOM results. The sc‐PLA complexes (nucleated PHB crystals) exhibit much small spherulite sizes but possess the same crystal cell morphology as that of neat PHB based on the WAXD result. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Effect of 1,3,5‐trialkyl‐benzenetricarboxylamide on the crystallization of poly(lactic acid)

A series of 1,3,5‐trialkyl‐benzenetricarboxylamides (BTA‐Rs) with different side‐chain lengths of n‐alkyl are synthesized to use as nucleating agents of poly (lactic acid) (PLA). Crystallization rate of PLA is detailed discussed in nonisothermal melt‐crystallization with addition of the synthesized nucleating agents. Among these BTA‐Rs, BTA‐n‐butyl (BTA‐nBu) shows the most excellent nucleation ability for PLA. The influences of BTA‐nBu on the nonisothermal melt‐crystallization and cold‐crystallization from the glassy state, isothermal crystallization, crystalline structure, and spherulite morphology of PLA are investigated. It is found that 0.8 wt % is the optimal weight fraction of BTA‐nBu to improve the crystallization of PLA. In the case of isothermal melt‐crystallization from melt, the addition of BTA‐nBu shortens the crystallization half‐time and speeds up the crystallization rate of PLA with no discernible effect on the crystalline structure. Besides, BTA‐nBu nucleated PLA exhibits smaller spherulites size and larger nucleation density than that of pure PLA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1328‐1336, 2013     

Miscibility and thermal and mechanical properties of melt‐mixed poly(lactic acid)/poly(trimethylene terephthalate)/(methyl methacrylate)‐butadiene‐styrene copolymer blends

This study examined the miscibility and mechanical properties of melt‐mixed poly(lactic acid) (PLA), poly (trimethylene terephthalate) (PTT), and PLA/PTT blend with 5–10 phr of methyl methacrylate‐butadiene‐styrene copolymer (MBS). The isothermal crystallization kinetics of the PTT blends were analyzed by using the Avrami equation. The Differential Scanning Calorimetry (DSC) and scanning electron microscope results indicated that the miscibility of the PLA/PTT blends was improved by adding 5–10 phr of MBS. Although PLA, with the addition of 10 phr of MBS, had lower tensile strength at yield and higher breaking elongation and impact strength than pure PLA, no improvement in these mechanical properties could be observed in PLA/PTT blends. This result is explained by assuming that the crystallization of PTT at the interface favors the disentanglement of MBS from the PTT domain. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Crystallization behavior,morphology, and mechanical properties of poly(lactic acid)/tributyl citrate/treated calcium carbonate composites

In this article, poly(lactic acid) (PLA) composites containing titanate coupling agent treated calcium carbonate (T‐CaCO₃) and tributyl citrate (TBC) were prepared via melt blending. The crystallization, morphology, mechanical properties, and nonisothermal cold crystallization kinetics of PLA composites were studied by means of differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD), polarized light microscopy (PLM), scanning electron microscopy (SEM), and mechanical tests, respectively. The results show that TBC promotes crystallization of PLA. Both T‐CaCO₃ and TBC significantly decrease the spherulitic size, but the crystal structure of PLA is not changed. A synergistic toughening effect is obtained by the combination of T‐CaCO₃ and TBC. The nonisothermal cold crystallization kinetics of PLA composites is well described by Mo's method. The activation energies (ΔE) of nonisothermal cold crystallization were calculated by Kissinger and Takhor methods, respectively. It is found that the addition of T‐CaCO₃ and TBC increases ΔE, but it also increases the cold crystallization rate. POLYM. COMPOS., 35:1570–1582, 2014. © 2013 Society of Plastics Engineers     

Nonisothermal crystallization kinetics of poly(lactide)—effect of plasticizers and nucleating agent

Poly(lactide), a bio‐based aliphatic polyester, is a subject to large research effort. One point of optimization is the acceleration of its crystallization kinetics to promote crystallinity under nonisothermal polymer processing conditions by means of compounding with nucleating agents and plasticizers. The nonisothermal crystallization kinetics of neat and formulated poly(L,D ‐lactide) (PDLLA) from the melt with talc and polyethylene glycol (PEG) or acetyl tributyl citrate (ATBC) were studied with the help of the Avrami–Jeziorny and Liu–Mo analysis. Talc showed to be a moderately efficient nucleating agent, as it causes only small increase of crystallization kinetics and shows no effect on the crystallization activation energy. A synergistic effect with plasticizers was observed, expanding the crystallization window significantly. PEG was found to be a more efficient plasticizer than ATBC but causes large decrease in the molecular weight average of PDLLA upon thermal treatment. The talc/ATBC system is efficient starting with an ATBC concentration of 9 wt%. The acceleration observed was a crystallization half‐time decrease of 30% compared to neat PLA and reaching maximum crystallization enthalpies even at cooling rate of 25°C min^?1. The ATBC/talc system can be recommended as an efficient system for acceleration of nonisothermal crystallization kinetics of PDLLA. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Effect of a small amount of poly(3‐hydroxybutyrate) on the crystallization behavior of poly(l‐lactic acid) in their immiscible and miscible blends during physical aging

The miscibility and effect of physical aging on the crystallization behavior of poly(l ‐lactic acid) (PLLA)/poly(3‐hydroxybutyrate) (PHB) blends with a small amount of PHB (≤10 wt%) have been investigated using differential scanning calorimetry and Fourier transform infrared spectroscopy. It is found that the miscibility of PLLA/PHB blends with a very small percentage of PHB can be modulated by varying the molecular weight of the PHB. That is, a PLLA/PHB blend with low‐molecular‐weight PHB is miscible, whereas that with high‐molecular‐weight PHB is immiscible. It is found that physical aging at temperatures far below the glass transition temperature can promote the cold crystallization kinetics of PLLA in PLLA/PHB blends with high‐molecular‐weight PHB rather than in those with low‐molecular‐weight PHB. These findings suggest that the effect of physical aging on the crystallization behavior of the main component in a crystalline/crystalline blend with a small percentage of the second component is strongly dependent on the miscibility of the blend system. Enhanced chain mobility of PLLA in the interface region of PLLA matrix and PHB micro‐domains is proposed to explain the physical aging‐enhanced crystallization rate in immiscible PLLA/PHB blends with high‐molecular‐weight PHB. © 2013 Society of Chemical Industry     

Morphology and properties of the biosourced poly(lactic acid)/poly(ethylene oxide‐b‐amide‐12) blends

Biosourced poly(lactic acid) (PLA) blends with different content of poly(ethylene oxide‐b‐amide‐12) (PEBA) were prepared by melt compounding. The miscibility, phase structure, crystallization behavior, mechanical properties, and toughening mechanism were investigated. The blend was an immiscible system with the PEBA domains evenly dispersed in the PLA matrix. The PEBA component suppressed the nonisothermal melt crystallization of PLA. With the addition of PEBA, marked improvement in toughness of PLA was achieved. The maximum for elongation at break and impact strength of the blend reached the level of 346% and 60.5 kJ/m², respectively. The phase morphology evolution in the PLA/PEBA blends after tensile and impact tests was investigated, and the corresponding toughening mechanism was discussed. It was found that the PLA matrix demonstrates obvious shear yielding in the blend during the tensile and impact tests, which induced energy dissipation and therefore lead to improvement in toughness of the PLA/PEBA blends. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Morphology,nonisothermal crystallization behavior,and kinetics of poly(phenylene sulfide)/polycarbonate blend

The morphology and nonisothermal crystallization behavior of blends made of poly(phenylene sulfide) (PPS), with a amorphous polycarbonate (PC) were studied. The blend is found to be partially miscible by the dynamic mechanical thermal analysis (DMTA) and melt rheological measurements. The nonisothermal crystallization behavior of blend was studied by differential scanning calorimetry (DSC). The results show clearly that the crystallization temperatures of PPS component in the blend decrease with increasing of PC contents. The crystallization kinetics was then analyzed by Avrami, Jeziorny, and Ozawa methods. It can be concluded that the addition of PC decreases the PPS overall crystallization rate because of the higher viscosity of PC and/or partial miscibility of blend, despite of small heterogeneous nucleation effect by the PC phase and/or phase interface. The results of the activation energy obtained by Kissinger method further confirm that the amorphous PC in the partial miscible PPS/PC blend may act as a crystallization inhibitor of PPS. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Miscibility,thermal behaviour,morphology and mechanical properties of binary blends of poly[(R)‐3‐hydroxybutyrate] with poly(γ‐benzyl‐L‐glutamate)+

The miscibility, thermal behaviour, morphology and mechanical properties of poly[(R)‐3‐hydroxybutyrate] (PHB) with poly(γ‐benzyl‐L ‐glutamate) (PBLG) are investigated by means of differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and tensile tests. The DSC results show that PHB and PBLG are immiscible in the melt state. Such immiscibility also exists in the amorphous state due to a clear two‐phase separated structure observed by SEM measurements. The blend samples with different thermal history, namely as original and melt samples separately, display differences in thermal behaviour such as the DSC scan profile, the crystallinity and the melting temperature of PHB. The crystallization of PHB both from the molten state and the amorphous state is retarded on addition of the second component. The SEM measurements reveal that a phase inversion occurs between the PHB/PBLG (60/40) and PHB/PBLG (40/60) blends. Except for the PHB/PBLG (40/60) blend, a microphase separated structure is observed for all blend compositions. The mechanical properties vary considerably with blend composition. Compared with pure components, the PHB/PBLG (20/80) blend shows a certain improvement in mechanical properties. © 2001 Society of Chemical Industry     

Effect of biobased and biodegradable nucleating agent on the isothermal crystallization of poly(lactic acid)

The effect of chemically modified thermoplastic starch (CMPS) on the thermal properties and isothermal crystallization kinetics of poly(lactic acid) (PLA) was studied by differential scanning calorimetry (DSC) and compared to that of granular starch and an inorganic nucleating agent, talc. Nucleated PLA showed an additional crystallization of PLA, which affected the melting temperature. The crystallinity and crystallization rate of PLA were considerably enhanced by addition of CMPS, even at 0.1% content, and the amount of the CMPS had little effect on the thermal properties and isothermal crystallization kinetics of PLA. The effect of CMPS as a nucleating agent was comparable to that of granular starch but slightly less than that of talc. However, CMPS can offer a fully biodegradable nucleating agent with no residues remaining for the biobased and biodegradable polymers.     

Fast crystallization of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) with talc and boron nitride as nucleating agents

The crystallization behavior of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) induced by two kinds of nucleating agents, boron nitride (BN) and talc, was investigated by differential scanning calorimetry, polarized optical microscopy and X‐ray diffraction. Both BN and talc have good nucleating ability in the crystallization of PHB and PHBV. From these results, combined with molecular weight measurement by gel permeation chromatography, the mechanism of nucleation by BN and talc in the crystallization of PHB and PHBV has been proposed. BN acts as a nucleating agent itself and initiates nucleation in the crystallization of PHB and PHBV. Talc acts in a different way. It reacts as a chemical reagent with the molten chains of PHB/PHBV, while the reaction product acts as the true nucleating agent, which lowers the crystallization barriers of PHB and PHBV. ¹H NMR spectroscopy provides evidence for the reaction between PHB and talc and supports the proposed nucleation mechanism. Copyright © 2005 Society of Chemical Industry     

成核剂对PET非等温结晶动力学的影响

利用差示扫描量热仪(DSC)研究了滑石粉、苯甲酸钠和离子聚合物Surlyn对聚对苯二甲酸乙二醇酯(PET)非等温结晶行为的影响,并用Ozawa模型计算了非等温结晶动力学参数。结果表明:三种成核剂均是PET的良成核剂,其中苯甲酸钠的成核效果最为显著。与纯PET相比,三种成核剂的加入均使PET的结晶峰温度Tmc向高温偏移,过冷度(Tm-Tmc)明显降低,结晶速率常数K明显增大。纯PET和PET/成核剂共混体系的Ozawa指数n值介于1-4之间,均不为整数,且PET/成核剂共混体系的Ozawa指数n值小于纯PET的n值。     

Investigation on the crystallization behavior of poly(ether ether ketone)/poly(phenylene sulfide) blends

The morphology of nonisothermally crystallized poly(phenylene sulfide) (PPS) and its blend with poly (ether ether ketone) (PEEK) have been observed by polarized optical microscope (POM) equipped with a hot stage. The nonisothermal crystallization behavior of PPS and PEEK/PPS blend has also been investigated by differential scanning calorimetry (DSC). The maximum crystallization temperature for PEEK/PPS blend is about 15°C higher than that of neat PPS, and the crystallization rate, characterized by half crystallization time, of the PEEK/PPS blend is also higher than that of the neat PPS. These results indicate that the PEEK acts as an effective nucleation agent and greatly accelerates the crystallization rate of PPS. The Ozawa model was used to analyze the nonisothermal crystallization kinetics of PPS and its blends. The Avrami exponent values of neat PPS are higher than that of its blend, which shows that the presence of PEEK changed the nucleation type of PPS from homogeneous nucleation to heterogeneous nucleation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Biodegradable polymer blends of poly(3-hydroxybutyrate) and poly(DL-lactide)-co-poly(ethylene glycol)

The melting and crystallization behavior and phase morphology of poly(3-hydroxybutyrate) (PHB) and poly(DL-lactide)-co-poly(ethylene glycol) (PELA) blends were studied by DSC, SEM, and polarizing optical microscopy. The melting temperatures of PHB in the blends showed a slight shift, and the melting enthalpy of the blends decreased linearly with the increase of PELA content. The glass transition temperatures of PHB/PELA (60/40), (40/60), and (20/80) blends were found at about 30°C, close to that of the pure PELA component, during DSC heating runs for the original samples and samples after cooling from the melt at a rate of 20°C/min. After a DSC cooling run at a rate of 100°C/min, the blends showed glass transitions in the range of 10–30°C. Uniform distribution of two phases in the blends was observed by SEM. The crystallization of PHB in the blends from both the melt and the glassy state was affected by the PELA component. When crystallized from the melt during the DSC nonisothermal crystallization run at a rate of 20°C/min, the temperatures of crystallization decreased with the increase of PELA content. Compared with pure PHB, the cold crystallization peaks of PHB in the blends shifted to higher temperatures. Well-defined spherulites of PHB were found in both pure PHB and the blends with PHB content of 80 or 60%. The growth of spherulites of PHB in the blends was affected significantly by 60% PELA content. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1849–1856, 1997     

Effect of boron nitride as a nucleating agent on the crystallization of bacterial poly(3‐hydroxybutyrate)

Different concentrations of boron nitride (BN) (0.2–0.8 wt %) are added to poly (3‐hydroxybutyrate) (PHB) as a nucleating agent. Polarized Optical Microscopy (POM) coupled to Differential Scanning Calorimetry (DSC) allow to monitor the isothermal and nonisothermal crystallization of neat and nucleated PHBs. It is found that the addition of BN to PHB modifies the mechanisms of crystallization without changing the crystallinity degree. DSC can replace POM whenever POM does not allow to estimate the spherulites growth rate. The Hoffman‐Lauritzen theory is used to explain the role of BN. The nucleating agent allows polymer crystallization at lower supercooling degrees. The regime II of crystallization is observed for nucleated PHBs. A modification of the coupling effect between the amorphous and the crystalline phases is evidenced. It is shown that a concentration of 0.2 wt % BN is sufficient to decrease the glass transition temperature and modify the crystallization mechanisms of PHB. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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