Highly improved crystallization behavior of poly(L‐lactide) induced by a novel nucleating agent: substituted‐aryl phosphate salts

In this work, a novel nucleating agent (NA) based on substituted‐aryl phosphate salts was introduced into poly(L‐Lactide) (PLLA). The nonisothermal and isothermal crystallization behaviors of nucleated PLLA samples were investigated through differential scanning calorimetry (DSC), wide angle X‐ray diffraction, and polarized optical microscope (POM). Furthermore, the effect of annealing treatment on the cold crystallization behaviors of nucleated samples was also investigated. The results show that the crystallization of PLLA, whether for the melt crystallization (including nonisothermal and isothermal crystallization process) or for the cold crystallization (including the cold crystallization occurring during the DSC heating process and during the annealing process), is greatly dependent upon the content of NA. At relatively lower NA content (≤0.1 wt%), the nucleation effect of NA is inconspicuous, however, at higher NA content (≥0.2 wt%), it exhibits great nucleation effect for the crystallization of PLLA. Further results show that the double endothermic peak of PLLA depends on the temperature applied for the crystallization. Copyright © 2012 John Wiley & Sons, Ltd.     

Poly(L‐lactide)/layered double hydroxides nanocomposites: Preparation and crystallization behavior

Novel nanocomposites from poly(L ‐lactide) (PLLA) and an organically modified layered double hydroxide (LDH) were prepared using the melt‐mixing technique. The structure and crystallization behavior of these nanocomposites were investigated by means of wide‐angle X‐ray diffraction (WAXD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and polarized optical microscopy (POM). WAXD results indicate that the layer distance of dodecyl sulfate‐modified LDH (LDH‐DS) is increased in the PLLA/LDH composites, compared with the organically modified LDH. TEM analysis suggests that the most LDH‐DS layers disperse homogenously in the PLLA matrix in the nanometer scale with the intercalated or exfoliated structures. It was found that the incorporation of LDH‐DS has little or no discernable effect on the crystalline structure as well as the melting behavior of PLLA. However, the crystallization rate of PLLA increases with the addition of LDH‐DS. With the incorporation of 2.5 wt % LDH‐DS, the PLLA crystallization can be finished during the cooling process at 5 °C/min. With the addition of 5 wt % LDH‐DS, the half‐times of isothermal melt‐crystallization of PLLA at 100 and 120 °C reduce to 44.4% and 57.0% of those of the neat PLLA, respectively. POM observation shows that the nucleation density increases and the spherulite size of PLLA reduces distinctly with the presence of LDH‐DS. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2222–2233, 2008     

光学纯度对聚左旋乳酸结晶与熔融行为的影响

通过示差扫描量热仪(DSC)和广角X射线衍射仪(WAXD)研究了聚左旋乳酸(PLLA)的光学纯度(91.6%、93.3%、94.0%、97.0%、98.4%)对聚乳酸结晶和熔融行为的影响。 在非等温结晶过程中,随着光学纯度的提高,聚乳酸的结晶峰值温度、熔点、熔融焓均提高。 在等温结晶过程中,PLLA的半结晶时间(t_1/2)随着光学纯度的增加而减少,在结晶温度100~110 ℃区间内半结晶时间均达到最小值;含有不同光学纯度PLLA的Avrami指数n≈3,表明光学纯度的变化不能改变聚乳酸以三维球晶生长的异相成核机理。 随着光学纯度的增加,聚乳酸δ-晶型转变为α-晶型的临界温度升高。 聚乳酸的结晶和熔融行为对光学纯度具有依赖性。     

Study of the crystallization behaviors of isotactic polypropylene with sodium benzoate as a specific versatile nucleating agent

Sodium benzoate (SB), a conventional nucleating agent of α‐phase isotactic polypropylene (iPP) was discovered to induce the creation of β‐phase iPP under certain crystalline conditions. Polarized optical microscopy (POM) and wide angle X‐ray diffraction (WAXD) were carried out to verify the versatile nucleating activity of SB and investigate the influences of SB's content, isothermal crystallization temperature, and crystallization time on the formation of β‐phase iPP. The current experimental results indicated that, under isothermal crystallization conditions, SB showed peculiar nucleating characteristics on inducing iPP crystallization which were different from those of the commercial β form nucleating agent (TMB‐5). The content of β crystal form of iPP nucleated with SB (PP/SB) increased initially with the increase of crystallization temperature, nucleating agent (SB) percentage or crystallization time, reached a maximum value, and then decreased as the crystallization temperature, nucleating agent percentage or crystallization time further increased. While the content of β crystal form of iPP nucleated with TMB‐5 (PP/TMB‐5) showed a completely different changing pattern with the crystallization conditions. The obvious difference of the two kinds of nucleating agents on inducing iPP crystallization can be explained by the versatile nucleating ability of SB. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1183–1192, 2008     

Cooperative effects of nucleation agent and plasticizer on crystallization properties of stereocomplex‐type poly(lactide acid)

An investigation of the cooperative effects of plasticizer (PEG) and nucleation agent (TMC‐306) on stereocomplex‐type poly(lactide acid) formation and crystallization behaviors between poly(L‐lactide acid) (PLLA) and poly(D‐lactide acid) (PDLA) was conducted. Wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC) analysis indicated that exclusive stereocomplex‐type poly(lactide acid) (sc‐PLA) crystallites without any homocrystallites poly(lactide acid) (hc‐PLA) did form by incorporation of PEG, TMC‐306, or both at a processing temperature higher than the melting temperature of sc‐PLA (around 230°C). The non‐isothermal and isothermal crystallization kinetics showed that PEG and TMC‐306 could independently accelerate the crystallization rate of sc‐PLA. The crystallization peak temperature and crystallization rate of sc‐PLA were significantly improved by the presence of PEG and TMC‐306. The influence of PEG and TMC‐306 on the morphologies of sc‐PLA was also investigated using polarized optical microscopy (POM). Copyright © 2016 John Wiley & Sons, Ltd.     

Crystallization behavior and morphology of β‐nucleated isotactic polypropylene with different stereo‐defect distribution

Aiming at further investigating the combination effect of concentration of β‐nucleating agent (β‐NA) and stereo‐defect distribution on the crystallization behavior of β‐nucleated isotactic polypropylene (β‐iPP), in this study, the crystallization behavior and polymorphic morphology of twoβ‐iPP resins with nearly same average isotacticity (PP‐A and PP‐B) but different uniformities of stereo‐defect distribution were investigated by differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD) and polarized optical microscopy (POM). The results of DSC and WAXD showed that the addition of TMB‐5 increases the crystallization temperature and decreases the spherulite sizes of both PP‐A and PP‐B, and reduces their crystallization energy barriers as well; however, the polymorphic behaviors of PP‐A and PP‐B exhibit different dependence on the TMB‐5 concentration. For PP‐A with less uniform distribution of stereo‐defects, β‐phase can be observed only when the TMB‐5 concentration is no less than 0.1 wt.%, while for PP‐B with more uniform stereo‐defect distribution, addition of 0.01 wt.% TMB‐5 can induce the formation of β‐phase. Moreover, the analysis of POM indicated that the crystalline morphologies of both PP‐A and PP‐B change greatly with the TMB‐5 concentration, and the variation features of PP‐A and PP‐B are quite different from each other. PP‐B with more uniform stereo‐defect distribution was more favorable for the formation of large amount of β‐phase in the presence of wide concentration range of TMB‐5. The different polymorphic behaviors and their different dependences on the β‐NA concentration were related to the different uniformities of stereo‐defect distribution of the samples, since the distribution of stereo‐defects could restrain the regular insertion of molecular chains during crystallization and thus determine the tendency the α‐phase crystallization of the sample. Copyright © 2014 John Wiley & Sons, Ltd.     

Crystallization kinetics and morphology of biodegradable poly(lactic acid) with a hydrazide nucleating agent

The effect of tetramethylenedicarboxylic dibenzoylhydrazide (designated here as TMC) on the nonisothermal and isothermal crystallization behavior of PLA was investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD). TMC shows excellent nucleating effect on PLA. With the addition of 0.05 wt% TMC, the crystallization half-time of PLA decreases from 26.06 to 6.13 min at 130 °C. The isothermal crystallization data were further analyzed by the Avrami model. The values of the Avrami exponent of the blends are comparable to that of neat PLA, indicating that the presence of TMC does not change the crystallization mechanism of the matrix. The observation from POM and WAXD measurements showed that the presence of TMC increases significantly the nuclei density of PLA but has no discernible effect on its crystalline structure.     

Crystallization behavior and morphology of poly(ethylene‐co‐trimethylene terephthalate)s

The melt crystallization behaviors and crystalline structures of poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate), and poly(ethylene‐co‐trimethylene terephthalate) (PETT) were investigated with differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X‐ray diffraction at various crystallization temperatures (T_cs). The PETT copolymers were synthesized via the polycondensation of terephthalate with ethylene glycol and trimethylene glycol (TG) in various compositions. The copolymers with 69.0 mol % or more TG or 31.0 mol % or less TG were crystallizable, but the other copolymers containing 34–56 mol % TG were amorphous. The DSC isothermal results revealed that the addition of a small amount of flexible TG (up to 21 mol %) to the PET structure slightly reduced the formation of three‐dimensional spherulites. A greater TG concentration (91–100%) in the copolyesters changed the crystal growth from two‐dimensional to three‐dimensional. The DSC heating scans after the completion of isothermal crystallization at various T_cs showed three melting endotherms for PET, PETT‐88, PETT‐84, and PETT‐79 and four melting endotherms for PETT‐9 and PETT. The presence of an additional melting endotherm could be attributed to the melting of thinner and imperfect copolyester crystallites. Analyses of the Lauritzen–Hoffman equation demonstrated that PETT‐88 had the highest values of the product of the lateral and folding surface free energies, and this suggested that the addition of small amounts of flexible trimethylene terephthalate segments to PET disturbed chain regularity, thus increasing molecular chain mobility. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4255–4271, 2004     

Crystallization kinetics and morphology of poly(butylene succinate‐co‐adipate)

The crystallization kinetics of biodegradable poly(butylene succinate‐co‐adipate) (PBS/A) copolyester was investigated by using differential scanning calorimetry (DSC) and polarized optical microscopy (POM), respectively. The Avrami and Ozawa equations were used to analyze the isothermal and nonisothermal crystallization kinetics, respectively. By using wide‐angle X‐ray diffraction (WAXD), PBS/A was identified to have the same crystal structure with that of PBS. The spherulitic growth rates of PBS/A measured in isothermal conditions are very well comparable with those measured by nonisothermal procedures (cooling rates ranged from 0.5 to 15 °C/min). The kinetic data were examined with the Hoffman–Lauritzen nucleation theory. The observed spherulites of PBS/A with different shapes and textures strongly depend on the crystallization temperatures. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3231–3241, 2005     

4,4'-二羟基二苯硫醚对聚甲醛结晶和熔融行为的影响

为了探究4,4'-二羟基二苯硫醚(TDP)的添加对聚甲醛(POM)熔融与结晶行为的影响,本文利用熔融共混的方法制备了POM/TDP共混材料。通过差示扫描量热仪(DSC)对共混材料的熔融与结晶行为进行了研究,利用广角X射线衍射仪(WAXD)对共混材料的晶体结构进行了研究。结果表明,在POM中添加TDP后,POM的晶面间距变大,晶体结构变的疏松,使POM的结晶温度(Tc)、结晶焓(ΔHc)、熔融温度(Tm)与熔融焓(ΔHm)均降低。当TDP质量分数增加到30%时,共混物的熔点与结晶温度较纯POM分别下降了15.2和12.8℃。在等温结晶过程中,随着TDP含量的增大,POM完成结晶所需的时间显著加长,共混物的结晶速率逐渐降低,结晶活化能逐渐升高,但TDP的加入对POM的晶型并没有影响。以上结果说明TDP的添加对POM的熔融与结晶行为影响很大,这将为POM结晶行为的调控提供依据。     

A new route of manipulation of poly(L‐lactic acid) crystallization by self‐assembly of p‐tert‐butylcalix[8]arene and toluene

A novel nucleating agent (TBC8‐t), self‐assembled with p‐tert‐butylcalix[8]arene (TBC8) and toluene, was used to manipulate the crystallization behavior of poly(L ‐lactic acid) (PLLA). Toluene molecules were used to adjust the crystallization structure of TBC8. Differential scanning calorimetry results show that the crystallization peak temperature (T_c) and crystallization rate (ΔH_c/time) of PLLA nucleated with TBC8‐t are 132.3 °C and 0.24 J/gs, respectively, which are much higher than that with conventional nucleating agent‐talc (T_c = 119.3 °C, ΔH_c/time = 0.13 J/gs). The results of polarized optical microscopy demonstrate that TBC8‐t could greatly enhance the crystallization rate of PLLA by increasing the nucleation rate rather than crystal growth rate. Along with an improvement of the crystallization rate, the crystalline morphology of PLLA is also affected by TBC8‐t. The addition of TBC8‐t transforms most of the original spherulite crystals into sheaf‐like crystals. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1235–1243, 2010     

Crystallization kinetics and morphology of biodegradable poly(butylene succinate‐co‐propylene succinate)s

The crystallization behavior of biodegradable poly(butylene succinate) and copolyesters poly(butylene succinate‐co‐propylene succinate)s (PBSPS) was investigated by using ¹H NMR, DSC and POM, respectively. Isothermal crystallization kinetics of the polyesters has been analyzed by the Avrami equation. The 2.2‐2.8 range of Avrami exponential n indicated that the crystallization mechanism was a heterogeneous nucleation with spherical growth geometry in the crystallization process of polyesters. Multiple melting peaks were observed during heating process after isothermal crystallization, and it could be explained by the melting and recrystallization model. PBSPS was identified to have the same crystal structure with that of PBS by using wide‐angle X‐ray diffraction (WAXD), suggesting that only BS unit crystallized while the PS unit was in an amorphous state. The crystal structure of polyesters was not affected by the crystallization temperatures, too. Besides the normal extinction crosses under the POM, the double‐banded extinction patterns with periodic distance along the radial direction were also observed in the spherulites of PBS and PBSPS. The morphology of spherulites strongly depended on the crystallization temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 420–428, 2007     

Preparation and characterization of benzoyl‐hydrazide‐derivatized poly(lactic acid) and γ‐cyclodextrin inclusion complex and its effect on the performance of poly(lactic acid)

A nucleating agent, benzyl‐hydrazide‐derivatized poly(lactic acid) (PLA) and γ‐cyclodextrin inclusion complex (PLA‐IC‐BH), was synthesized through a series of reactions. Poly(lactic acid) and γ‐cyclodextrin inclusion complex (PLA‐IC) was first obtained by ultrasonic co‐precipitation, which was then subjected to carboxylation, acylation, and amidation using benzoyl hydrazine and thionyl chloride. The composition and structure of PLA‐IC‐BH was confirmed by ¹H nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction. PLA/PLA‐IC‐BH composites were prepared by melt blending and a hot‐press forming process. Mechanical properties, thermal stabilities, and crystallization behaviors of PLA/PLA‐IC‐BH samples were investigated by thermogravimetric analysis, differential scanning calorimetry (DSC), polarized optical microscopy (POM), rheological analysis, and so on. Mechanical testing and thermogravimetric analysis showed that the tensile strengths, impact properties, and thermal stabilities of PLA/PLA‐IC‐BH composites were improved significantly compared to pure PLA and PLA/PLA‐IC. DSC results showed that crystallinity of PLA was increased from 5.17% to 38.93% after introduction of PLA‐IC‐BH. POM results showed that PLA‐IC‐BH acted as a nucleating agent for PLA and enhanced its crystallization rate. Rotational rheological behaviors of PLA/PLA‐IC‐BH demonstrated that incorporation of PLA‐IC‐BH increased the rigidity of the network structure of the PLA matrix. Compared to those of PLA, the maximum torque and apparent viscosity of PLA/PLA‐IC‐BH composites were increased by 55.56% and 25.59%, respectively. Copyright © 2017 John Wiley & Sons, Ltd.     

Effects of functionalized graphenes on the isothermal crystallization of poly(L-lactide) nanocomposites

The effects of graphene oxide(GO) with polar groups and functionalized GO(f GO) with nonpolar groups on the isothermal crystallization of poly(L-lactide)(PLLA) were compared. Functionalized GO was obtained by grafting octadecylamine and characterized by FTIR, WAXD and TGA. Isothermal crystallization kinetics of PLLA/GO and PLLA/f GO nanocomposites were investigated by combining DSC data and Avrami equation. The results showed that f GO could improve PLLA crystallization rate more obviously than GO. By analyzing the morphology obtained from POM, SEM and TEM, it was found f GO with large layer space dispersed better in PLLA and supplied more nucleation sites than GO. Therefore, for the multilayer graphene, increasing the layer spaces is important to improve its dispersion in polymers, which will cause the crystal kinetics changing of polymers.     

Rheology and crystallization behavior of PLLA/TiO2‐g‐PDLA composites

Poly(L‐lactide) (PLLA) composites with TiO₂‐g‐poly(D‐lactide) (PDLA), which was synthesized by surface‐initiated opening ring polymerization with TiO₂ as initiator and Sn(Oct)₂ as catalyst, were prepared by solution casting. The synthesized TiO₂‐g‐PDLA was characterized by transmission electron microscope (TEM) and dynamic laser scattering (DLS), showing larger size corresponding to that of TiO₂. Fourier transform infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectroscopy (XPS) measurements were further carried out and indicated that PDLA was grafted onto TiO₂ through covalent bond. For PLLA/TiO₂‐g‐PDLA composites, the stereocomplex crystallites were formed between PDLA grafted on the surface of TiO₂ and the PLLA matrix, which was determined by FT‐IR, differential scanning calorimetry (DSC), and X‐ray diffractometer (XRD). The influence of stereocomplex crystallites on the rheological behavior of PLLA/TiO₂‐g‐PDLA was investigated by rheometer, which showed greater improvement of rheological properties compared to that of PLLA/TiO₂ composites especially with a percolation content of TiO₂‐g‐PDLA between 3 wt%–5 wt%. The crystallization and melting behavior of PLLA/TiO₂‐g‐PDLA composites were studied by DSC under different thermal treatment conditions. The formed PLA stereocomplex network acted as nucleating agents and a special interphase on the functional surface of TiO₂, which resulted in imperfect PLLA crystal with lower melting temperature. When the thermal treatment was close to the melting temperature of PLA stereocomplex, the crystallinity approached to the maximum. The isothermal crystallization study by polarizing microscope (POM) indicated that stereocomplex network presented stronger nucleation capacity than TiO₂‐g‐PDLA. Copyright © 2015 John Wiley & Sons, Ltd.     

Analysis of crystallization behavior and crystal modifications of poly(butylene‐2,6‐naphthalene dicarboxylate)

Information on the crystalline structure and the properties of poly(butylene‐2,6‐naphthalene dicarboxylate) (PBN) has not been well reported until now, but it is known that there are two different crystal modifications in PBN, as follows: one is formed in isotropic samples by annealing (α form); another appears by annealing with tension (β form). The relation between the crystal modifications and the kinetics of isothermal crystallization for PBN was investigated using in‐situ Fourier transform infrared spectroscopy (FTIR) and wide‐angle X‐ray diffraction (WAXD). The melting behavior of each crystalline form was also studied by means of FTIR and differential scanning calorimetry (DSC) measurements. From the analysis of the melt‐crystallized PBN specimens, the two crystalline forms coexisted in the isotropic samples melt‐crystallized at 230°C, but only the α crystal modification was observed in the films annealed at lower temperatures. In addition, it was revealed that, at 230°C, the β modification was formed only in the primary crystallization process. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 561–574, 1999     

Synergistic effects of PEG and MWCNTs on crystallization behavior of PLLA

This work reported the crystallization behaviors of poly(L ‐lactide) (PLLA) with the presence of polyethylene glycol (PEG) and/or functionalized multiwalled carbon nanotubes (FMWCNTs). The crystallization behaviors occurred in the different conditions, including nonisothermal, isothermal and during the annealing process, were analyzed comparatively using differential scanning calorimetry, wide angle X‐ray diffraction, and polarized optical microscope. The results show that PEG as an efficient plasticizer of PLLA enhances the mobility of PLLA chain segments, which leads to the decrease of glass transition temperature and the enhancement of crystallization ability of PLLA. FMWCNTs as a nucleating agent of PLLA crystallization promote the crystallization of PLLA apparently. With the presence of PEG and FMWCNTs, the crystallization of PLLA is well improved in all conditions, indicating the synergistic effects of PEG and FMWCNTs on PLLA crystallization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 520–528, 2010     

Effect of the γ‐form crystal on the thermal fractionation of poly(propylene‐co‐ethylene)

The effect of the γ‐form crystal on the thermal fractionation of a commercial poly(propylene‐co‐ethylene) (PPE) has been studied by differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD) techniques. Two thermal fractionation techniques, stepwise isothermal crystallization (SIC) and successive self‐nucleation and annealing (SSA), have been used to characterize the molecular heterogeneity of the PPE. The results indicate that the SSA technique possesses a stronger fractionation ability than that of the SIC technique. The heating scan of the SSA fractionated sample exhibits 12 endothermic peaks, whereas the scan of the SIC fractionated sample only shows eight melting peaks. The WAXD observations of the fractionated PPE samples prove that the content of the γ‐form crystals formed during the thermal treatment of the SIC technique is much higher than that of the SSA treatment. The former is 57.4%, whereas the later is 12.6%. The effect of theγ‐form crystals on thermal fractionation ability is discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4320–4325, 2004     

Poly(phenylene sulfide)/low‐melting‐point metal composites. I. Transient viscoelastic properties and crystallization kinetics

Poly(phenylene sulfide)/low‐melting‐point metal composites (PPSMs) with various loading levels were prepared by melt compounding. The nonisothermal crystallization behavior and transient viscoelastic properties were characterized by the DSC, POM, DMA, and parallel‐plate rheometer. The results reveal that the low‐melting‐point metal (LMPM) particles show nice dispersion at relative low content levels (< 30 wt %). The PPSMs composites present dual characteristics of both the filled polymer composite and polymer blend system in their transient viscoelastic behaviors, which results in occurrence of the stress overshoots with long relaxation time and nonzero residual stress especially at high shear levels. During the crystallization process, the presence of those deformable LMPM droplets facilitates the crystallization kinetics of PPS because of their flow‐promoting action. On the other hand, the LMPM has no heterogeneous nucleating effect and, only plays the role of inert filler, which results in the degradation of the crystal structure of PPS. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 677–690, 2008     

溶剂诱导的聚乳酸/聚乳酸衍生物共结晶行为

通过溶液浇铸法制备不同组分的左旋聚乳酸(PLLA)和聚(L-2-羟基-3-甲基丁酸)(PL-2H3MB)共混物.运用差示扫描量热仪(DSC)、偏光显微镜(POM)、广角X射线衍射(WAXD)和热重分析仪(TGA)分析共混物的结晶、熔融行为和热稳定性.通过观察到DSC加热曲线中新的熔融峰判断PLLA和PL-2H3MB共晶...