Isothermal crystallization kinetics of poly(lactic acid)/synthetic mica nanocomposites

The isothermal crystallization kinetics of PLA/fluoromica nanocomposites was studied. Three types of synthetic mica at three concentrations (2.5, 5.0, and 7.5 wt % mica) were used and the effect of these micas on the crystallization and thermal properties of PLA was investigated by differential scanning calorimetry (DSC). The Avrami and Hoffman‐Weeks equations were used to describe the isothermal crystallization kinetics and melting behavior. Addition of these micas to the PLA matrix increased the crystallization rate, and this effect depended on the mica type and concentration. While the nonmodified Somasif ME‐100 exerted the smallest effect, the effect observed for the organically modified Somasif MPE was the most pronounced. The lower half‐time of crystallization t_1/2 was around 3 min for the PLA/Somasif MPE nanocomposites containing 7.5 wt % of filler at 90°C, which is about 16 min below that found for neat PLA. The equilibrium melting temperature ( ) of PLA were estimated for these systems, showing an increase in the composites and an increase with increasing loading, except for PLA/Somasif MPE, in which the increase of the mica content decreased about 5°C. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40322.     

Isothermal crystallization and melting behavior of polypropylene with lanthanum complex of cyclodextrin derivative as a β‐nucleating agent

A novel highly active β‐nucleating agent, β‐cyclodextrin complex with lanthanum (β‐CD‐MAH‐La), was introduced to isotactic polypropylene (iPP). Its influence on isothermal crystallization and melting behavior of iPP was investigated by differential scanning calorimeter (DSC), wide‐angle X‐ray diffraction (WAXD), and polarized light microscopy (PLM). WAXD results demonstrated that β‐CD‐MAH‐La was an effective β‐nucleating agent, with β‐crystal content of iPP being strongly influenced by the content of β‐CD‐MAH‐La and the isothermal crystallization temperature. The isothermal crystallization kinetics of pure iPP and iPP/β‐CD‐MAH‐La was described appropriately by Avrami equation, and results revealed that β‐CD‐MAH‐La promoted heterogeneous nucleation and accelerated the crystallization of iPP. In addition, the equilibrium melting temperature (T) of samples was determined using linear and nonlinear Hoffman‐Weeks procedure. Finally, the Lauritzen‐Hoffman secondary nucleation theory was applied to calculate the nucleation parameter (K_g) and the fold surface energy (σ_e), the value of which verify that the addition of β‐CD‐MAH‐La reduced the creation of new surface for β‐crystal and then led to faster crystallization rate. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influences of pre‐ordered melt structures on the crystallization behavior and polymorphic composition of β‐nucleated isotactic polypropylene with different stereo‐defect distribution

As part of continuous efforts to understand the surprising synergetic effect between β‐nucleating agent and pre‐ordered structures of isotactic polypropylene (iPP) in significant enhancement of β‐crystallization (Ordered Structure Effect, OSE), two β‐nucleated iPP with different uniformities of stereo‐defect distribution (WPP‐A and WPP‐B) were prepared, their crystallization behaviors with variation of melt structures were studied in detail. The results revealed that β‐phase can hardly form in WPP‐A (whose stereo‐defect distribution is less uniform) because of its strong tendency of α‐nucleation caused by its less uniform stereo‐defect distribution, while WPP‐B is more favorable for β‐crystallization; As fusion temperature decreases, similar variation trends of crystallization temperature and β‐phase proportion can be observed from WPP‐A and WPP‐B, indicating the occurrence of OSE behavior, which provides unsurpassed β‐nucleation efficiency and induces β‐crystallization even in WPP‐A which is less favorable for β‐crystallization; moreover, the upper and lower limiting temperatures of Region II of WPP‐A and WPP‐B are identical, suggesting the uniformity of stereo‐defect distribution has little influence on temperature window for OSE (denoted as Region II). To explore the physical nature of Region II, self‐nucleation behavior and equilibrium melting temperature of PP‐A and PP‐B were studied. The lower limiting temperatures of exclusive self‐nucleation domain of both PP‐A and PP‐B are identical with the lower limiting temperatures of Region II in OSE (168°C); moreover, the T_m⁰ of both PP‐A and PP‐B are close to their upper limiting temperatures of Region II in OSE behavior (189°C). The possible explanation was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42632.     

Self‐nucleation behaviors of olefinic blocky copolymer/montmorillonite nanocomposites with collapsed and intercalated clay layers

The self‐nucleation behavior of olefinic blocky copolymer (OBC) / organically modified montmorillonite (OMMT) nanocomposites with a novel collapsed clay structure (c‐OMMT) was studied and compared with that of the nanocomposites with an intercalated clay structure (OBC/i‐OMMT). Their behaviors appear different in three temperature domains, Domain I (D_I) in which the polymer is completely melted and only the heterogeneous nuclei are present, Domain II (D_II) in which only self‐nucleation occurs and Domain III (D_III) where both self‐nucleation and annealing take place. As the OMMT loading increases, the boundary temperature of D_I and D_II (T_I→II) shifts to lower temperature and D_II becomes narrower. For the OBC/c‐OMMT nanocomposites, the T_I→II or T_I→III (the boundary temperature of D_I and D_III) can be lower than the end melting temperature ( ) and leads to appearance of a subdomain of D_I, D_I′, in which the self‐nuclei of un‐melted fragmental crystals exist but the following crystallization is still initiated by c‐OMMT. D_II may even disappear at high c‐OMMT loadings. By contrast, the T_I→II of the OBC/i‐OMMT nanocomposites is always approximate to or higher than the . D_II does not disappear and no D_I′ is observed for the OBC/i‐OMMT nanocomposites. The nucleation efficiency of c‐OMMT is also evidently higher than that of i‐OMMT. These results verify that the c‐OMMT has stronger nucleation ability than i‐OMMT at the same OMMT loading. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41771.     

Thermal and dynamic mechanical properties of attapulgite reinforced poly(butylene succinate‐co‐1,2‐ octanediol succinate) nanocomposites

Attapulgite (ATP)‐reinforced poly(butylene succinate‐co‐1,2‐octanediol succinate) nanocomposites were fabricated using an in situ two‐step polymerization method. The transmission electron microscopy (TEM) results showed a superior interfacial linkage between ATP and PBS matrix. The isothermal crystallization kinetics results showed that ATP can effectively act as a nucleating agent, resulting in an enhancement on the crystallization temperature and crystallization rate. The incorporation of ATP nanoparticles probably induced heterogeneous nucleation that made the lower activation energy. The equilibrium melting temperature ( ) of the ATP reinforced branched copolymer also had little difference with the homogeneous PBS. The temperature at an initial thermal degradation was improved for the ATP reinforced branched nanocomposites. The dynamic mechanical analysis (DMA) results showed that there was a significant increase of storage modulus (E′) in an overall temperature range of all ATP reinforced nanocomposites. ATP had a strong effect on the elastic properties of the homogeneous PBS matrix. POLYM. COMPOS., 34:1126–1135, 2013. © 2013 Society of Plastics Engineers     

Unique crystallization behavior of isotactic polypropylene in the presence of l‐isoleucine and its inhibition and promotion mechanism of nucleation

l ‐Isoleucine (l ‐Ile) was identified as an efficient anti‐nucleating agent for isotactic polypropylene (iPP). At 0.08 wt %, l ‐Ile could significantly decrease the peak crystallization temperature (T_cp) of iPP by up to 8 °C at a cooling rate of 20 °C/min. Furthermore, l ‐Ile exhibited both anti‐nucleation and pro‐nucleation abilities; i.e., a low content of l ‐Ile inhibited iPP crystallization, whereas a high content promoted iPP crystallization. The unique crystallization behavior of iPP in the presence of l ‐Ile was investigated by differential scanning calorimetry, polarized optical microscopy (POM), and rheological measurement. According to POM, a low content of l ‐Ile completely dissolved in the iPP melt, whereas a high content of l ‐Ile did not. Therefore, a mechanism by which l ‐Ile inhibits and promotes the nucleation of iPP was proposed. Dissolving l ‐Ile molecules in the iPP melt hindered the homogeneous nucleation of iPP as a “dilution effect”; however, as the content increases, l ‐Ile could not be completely dissolved in molten iPP, and the residual crystals of l ‐Ile thus provided heterogeneous nucleation sites for iPP and further promoted its crystallization. Experimental evidence from rheology and POM supported this mechanism. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45956.     

Crystallization kinetics of maleic anhydride‐modified iPP studied by POM

Melt nucleation and crystallization behavior of homo‐isotatic polypropylene (homo‐iPP), maleic anhydride (MAH)‐grafted‐iPP, and MAH‐modified iPP, produced from iPP and a small amount of MAH‐grafted‐iPP, was investigated by polarizing optical microscopy (POM), at T_c = 121–135^oC. Nucleation processes at a given T_c were faster for modified PP as compared to neat iPP. The induction time for nucleation increased nonlinearly with increasing T_c and decreased for modified PP, probably as a result of promoted heterogeneous nucleation due to the presence of carbonyl groups of MAH‐grafted‐PP. The average spherulite sizes were decreased by modification, and the growth rate was enhanced in maleated PP and modified PP. The induction time approach was applied to the results obtained by POM to compare the tendency for heterogeneous nucleation of neat and MAH‐modified PP. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3107–3118, 2000     

Isothermal crystallization behavior of isotactic polypropylene blended with small loading of polyhedral oligomeric silsesquioxane

The isothermal crystallization kinetics and morphology development of isotactic polypropylene (iPP) blended with small loading of nanostructure of polyhedral oligomeric silsesquioxane (POSS) were studied with differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). The crystallization behaviors of iPP/POSS composites presented an unusual crystallization behavior during isothermal and nonisothermal crystallization conditions. The exothermic morphologies of isothermal and nonisothermal crystallization of iPP/POSS composites changed remarkably with increasing POSS. Moreover, the developments of spherulitic morphology for iPP/POSS composites showed that the major dispersed POSS molecules became nanocrystals first and then aggregated together forming thread- or network-like morphologies, respectively, depending on POSS content, which was observed. It implies that these major POSS nanocrystals' morphologies appeared as an effective nucleating agent and promoted the nucleation rate of iPP, whereas the minor dispersed POSS molecules that had slight miscibility between iPP retarded the nucleation and growth rates of iPP in the remaining bulk region. Therefore, the isothermal crystallization showed a single exothermic peak at pure iPP and POSS-1.0, whereas at POSS-2.0 and POSS-3.0, displayed the multi-exothermic peaks during isothermal crystallization. These faces indicated that POSS molecules were both influence on the transport of iPP chain in the melted state and on the free-energy of formation the critical nuclei of iPP assisted by the POSS structures were observed. Therefore, we postulated that the crystallization mechanisms of multi-exothermic peaks in isothermal crystallization may proceed to combine the “nucleating agent inducing nucleation of iPP event assisted by the POSS domains” that the nucleation of iPP does occur preferentially on the surfaces of the POSS “threads” or “networks” structures, and “nucleation and growth of iPP in the remaining bulk melted iPP region retarded by dispersed POSS molecules”. Therefore, effects of POSS content on the isothermal and nonisothermal crystallization behaviors of iPP/POSS composites due to the POSS molecules partially miscible with iPP, at very small loading of POSS molecules, promoted or retarded the rates of nucleation and growth of iPP depending on the POSS content and crystallization temperature were discussed.     

Influence of different β‐nucleating agent on crystallization behavior,morphology, and melting characteristic of multiwalled carbon nanotube‐filled isotactic polypropylene nanocomposites

To obtain isotactic polypropylene (iPP) nanocomposites with high β‐crystal content, TMB5, calcium pimelate and calcium pimelate supported on the surface of nano‐CaCO₃ were used as β‐nucleating agent and MWCNT filled β‐nucleated iPP nanocomposites were prepared. The effect of different β‐nucleating agent and MWCNT on the crystallization behavior and morphology, melting characteristic and β‐crystal content of β‐nucleated iPP nanocomposites were investigated by DSC, XRD and POM. The results indicated that addition of MWCNT increased the crystallization temperature of iPP and MWCNT filled iPP nanocomposites mainly formed α‐crystal. The β‐nucleating agent can induce the formation of β‐crystal in MWCNT filled iPP nanocomposites. The β‐nucleating ability and β‐crystal content in MWCNT filled β‐nucleated iPP nanocomposites decreased with increasing MWCNT content and increased with increasing β‐nucleating agent content due to the nucleation competition between MWCNT and β‐nucleating agents. It is found that the calcium pimelate supported on the surface of inorganic particles as β‐nucleating agent has stronger heterogeneous β‐nucleation than calcium pimelate and TMB5. The MWCNT filled iPP nanocomposites with high β‐crystal content can be obtained by supported β‐nucleating agent. POLYM. COMPOS., 36:635–643, 2015. © 2014 Society of Plastics Engineers     

Isotactic Poly(propylene) Nanocomposites Based upon Boehmite Nanofillers

The influence of boehmite crystallite sizes, varied between 10 and 60 nm, was studied with respect to the morphology development, crystallization behavior and mechanical properties of the boehmite‐based iPP nanocomposites. The nanometer‐scaled boehmites were formed during twin‐screw melt extrusion of iPP at 200 °C. Even in the absence of polymer compatibilizers, the boehmites, obtained from Sasol's process, enabled very effective deagglomeration and in‐situ dispersion of nanoboehmites. With increase in boehmite crystallite size it was possible to improve simultaneously stiffness and impact strength of iPP. As evidenced by means of DSC, POM and WAXS measurements, the deagglomerated nanoboehmites nucleated crystallization of poly(propylene)'s α‐modification.

     

Investigation of the crystallization behavior of isotactic polypropylene polymerized with different Ziegler‐Natta catalysts

Detailed characterization of the crystallization behavior is important for obtaining better structure property correlations of the isotactic polypropylene (iPP), however, attributed to the complexity in ZN‐iPP polymerization, the relationship between crystallization behavior and the stereo‐defect distribution of iPP is still under debate. In this study, the crystallization kinetics of the primary nucleation, crystal growth and overall crystallization of two iPP samples (PP‐A and PP‐B) with nearly same average isotacticity but different stereo‐defect distribution (the stereo‐defect distribution of PP‐B is more uniform than PP‐A) were investigated. The results of isothermal crystallization kinetics showed that the overall crystallization rate of PP‐A was much higher than that of PP‐B; but the analysis of self‐nucleation isothermal crystallization kinetics and the polarized optical microscopy (POM) observation indicated that the high overall crystallization rate of PP‐A was attributed to the high primary nucleation rate of the resin. The stereo‐defect distribution plays an important role in determining both the nucleation kinetics and crystal grow kinetics, and thus influence the overall crystallization kinetics. A more uniform distribution of stereo‐defects restrains the crystallization rate of iPP, moreover, it has more influence on nucleation kinetics, comparing with the crystal growth. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Physical Properties of Isotactic Poly(propylene)/Silver Nanocomposites: Dynamic Crystallization Behavior and Resultant Morphology

Summary: The presence of silver nanoparticles (0.01–5 wt.‐%) increased the crystallization temperature of isotactic poly(propylene) (iPP) (e.g., a 5 wt.‐% content increases the temperature by ca. 7 °C) and produced a sharper crystalline peak. It had little effect on the melt rheology of the nanocomposites. The shear‐induced crystallization behavior of iPP was accelerated with increasing Ag content and imposed frequency. In addition, the promoting effect of Ag nanoparticles on the overall crystallization behavior was more notable at 140 °C than at 130 °C. The wide‐angle X‐ray diffraction scans of iPP nanocomposites with 5 wt.‐% Ag crystallized at 130 °C clearly presented another peak at a 2θ value of 15.8°, which corresponded to a β‐form crystal. The nanocomposites with 5 wt.‐% Ag crystallized at 130 °C gave double melting peaks at 154 and 166 °C. On the other hand, the samples crystallized at 140 °C produced two melting peaks at 166 and 172 °C. The introduction of as much as 0.1 wt.‐% of Ag nanoparticles increased both the tensile strength and elongation at break, but subsequent further addition caused a decrease. In addition, iPP nanocomposites with more than 1 wt.‐% Ag exhibited a higher modulus than pure iPP.

Time dependence of G′ of iPP and iPP/Ag nanocomposites at 130 °C at ω = 1 rad · s^?1.     

Nonisothermal crystallization kinetics of polyoxymethylene/montmorillonite nanocomposite

The nonisothermal crystallization kinetics of polyoxymethylene (POM), polyoxymethylene/Na–montmorillonite (POM/Na–MMT), and polyoxymethylene/organic–montmorillonite (POM/organ–MMT) nanocomposites were investigated by differential scanning calorimetry at various cooling rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were employed to describe the nonisothermal crystallization process of POM/Na–MMT and POM/organ–MMT nanocomposites. The difference in the values of the exponent n between POM and POM/montmorillonite nanocomposites suggests that the nonisothermal crystallization of POM/Na–MMT and POM/organ–MMT nanocomposites corresponds to a tridimensional growth with heterogeneous nucleation. The values of half‐time and the parameter Z_c, which characterizes the kinetics of nonisothermal crystallization, show that the crystallization rate of either POM/Na–MMT or POM/organ–MMT nanocomposite is faster than that of virgin POM at a given cooling rate. The activation energies were evaluated by the Kissinger method and were 387.0, 330.3, and 328.6 kJ/mol for the nonisothermal crystallization of POM, POM/Na–MMT nanocomposite, and POM/organ–MMT nanocomposite, respectively. POM/montmorillonite nanocomposite can be as easily fabricated as the original polyoxymethylene, considering that the addition of montmorillonite, either Na–montmorillonite or organ–montmorillonite, may accelerate the overall nonisothermal crystallization process. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2281–2289, 2001     

Rheological studies on the quasi-quiescent crystallization of polypropylene nanocomposites

Isothermal crystallization of isotactic polypropylene (iPP)/organic montmorillonite (OMMT) binary nanocomposite and iPP/OMMT/poly(ethylene-co-octene) (PEOc) ternary nanocomposites has been investigated by polarized optical microscopy (POM), rheometry and scanning electron microscopy (SEM). At the stage of nucleation the heterogeneous nucleation effect of OMMT was much greater than the concentration fluctuation assisted nucleation effect in the ternary nanocomposite. Besides, PEOc played a role of inhibitor of OMMT nucleation agents at the nucleation stage because many of OMMT layers were distributed around PEOc-rich domains. At stage II of the crystal growth process, the entanglement effect of PEOc greatly affected the rheological response (storage modulus (G′) and its growth rate) due to the long side chains of PEOc component. In stage III of the growth process, OMMT layers and the entanglement of PEOc chains limited the motion of polypropylene chains. So the growth rate of G′ was slowed down. During the shrinkage and cooling process after isothermal crystallization, some fibril links between the spherulites, consisting of PEOc chains and iPP chains, were formed from the amorphous phases surrounding the spherulites.     

Isothermal and nonisothermal crystallization kinetics of isotactic polypropylene nucleated with substituted aromatic heterocyclic phosphate salts

The crystallization kinetics of isotactic polypropylene (iPP) and nucleated iPP with substituted aromatic heterocyclic phosphate salts were investigated by means of a differential scanning calorimeter under isothermal and nonisothermal conditions. During isothermal crystallization, Avrami equation was used to describe the crystallization kinetics. Moreover, kinetics parameters such as the Avrami exponent n, crystallization rate constant Z_t, and crystallization half‐time t_1/2 were compared. The results showed that a remarkable decrease in t_1/2 as well as a significant increase in overall crystallization rate was observed in the presence of monovalent salts of substituted aromatic heterocyclic phosphate, while bivalent and trivalent salts have little effect on crystallization rate of iPP. The addition of monovalent metal salts could decrease the interfacial free energy per unit area perpendicular to PP chains σ_e value of iPP so that the nucleation rate of iPP was increased. During nonisothermal crystallization, Caze method was used to analyze the crystallization kinetics. It also showed that monovalent metal salts had better nucleation effects than bivalent and trivalent metal salts. From the obtained Avrami exponents of iPP and nucleated iPP it could be concluded that the addition of different nucleating agents changed the crystal growth pattern of iPP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3307–3316, 2006     

Synthesis of aminated glycidyl methacrylate grafted rice husk and investigation of its anion‐adsorption properties

In this study, we focused on the synthesis, characterization, and adsorption capacity testing of aminated glycidyl methacrylate grafted rice husk (RH‐g‐GMA–Am). Our goal was to obtain a high‐performance surface for the adsorption of various anions. Glycidyl methacrylate grafted rice husk (RH‐g‐GMA) was prepared by the graft copolymerization of glycidyl methacrylate with rice husk; the product was further subjected to an amination reaction. The surface properties, sorption characteristic functional groups, isotherm and kinetic studies, pore diffusion models, and effects of the temperature and pH on the material properties were studied under batch conditions. The IR spectroscopy results show additional surface functional groups for RH‐g‐GMA–Am. The adsorptions of and on RH‐g‐GMA–Am were found to follow pseudo‐second‐order kinetics; this indicated a possible dominant role played by chemisorption. The rate‐limiting step for mass transfer was found to be boundary layer diffusion. Furthermore, the sorption isotherms for and fit the Langmuir model. The amination of RH‐g‐GMA drastically increased the removal efficiency from 3 to 82% and from 6 to 93% for and , respectively. Moreover, RH‐g‐GMA–Am exhibited a better removal efficiency in the pH range of 4–6.5. Regeneration studies revealed that the surface of RH‐g‐GMA–Am could be regenerated repetitively by simple acid washing with an insignificant decrease in the active surface for consecutive adsorptions. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43002.     

Mechanism of internal and external electron donor effects on propylene polymerization with MgCl2‐supported Ziegler–Natta catalyst: New evidences based on active center counting

Two TiCl₄/Di/MgCl₂ type supported Ziegler–Natta catalysts were prepared by loading dibutylphthalate or dicyclopentyldimethoxysilane (DCPDMS) (internal donor, Di) and TiCl₄ on activated δ‐MgCl₂ in sequence, and a blank catalyst was prepared by loading TiCl₄ on the same δ‐MgCl₂ without adding Di. These catalysts have similar specific surface area and pore size distribution, thus form a suitable base for comparative studies. Propylene polymerization with the catalysts was conducted in n‐heptane slurry using triethylaluminum (TEA) as cocatalyst, and the effects of Di as well as De (external donor, in this work it was DCPDMS) on the number of active centers, the distribution of active centers among three polypropylene (PP) fractions (isotactic, medium isotactic, and atactic PP chains), and chain propagation rate constants of the PP fractions were studied by counting the number of active centers in the PP fractions using a method based on selective quench‐labeling of the propagation chains by 2‐thiophenecarbonyl chloride. When De was not added in the polymerization, introducing a phthalate type Di in the catalyst evidently changed the active center distribution by enhancing the proportion of active centers producing isotactic PP (iPP) ( ), but scarcely changed reactivities of the three groups of active centers forming the three fractions. When the De was added in the polymerization system with TiCl₄/phthalate/MgCl₂ catalyst, further shifting of active center distribution in favor of took place, meanwhile reactivities of the three groups of active centers also remarkably changed in favor of . Mutual effects of these changes led to overwhelming dominance of iPP production in the TiCl₄/Di/MgCl₂–TEA/De system (Di = phthalate, De = alkoxysilane). In contrast, though using alkoxysilane as Di also caused shifting of active center distribution in favor of when De was not added, addition of alkoxysilane De caused reverse shifting of active center distribution in favor of those producing PP of lower stereoregularity. This unfavorable change largely counteracted the reactivity changes in favor of caused by the De, rendering the catalytic system rather poor isospecificity. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46605.     

Effect of sepiolite on the crystallization behavior of biodegradable poly(lactic acid) as an efficient nucleating agent

To enhance the crystallization kinetics of poly(lactic acid) (PLA), fibrous sepiolite was explored for nucleating the crystallization of PLA. PLA/sepiolite nanocomposites were prepared via the melt‐extrusion method. The effect of sepiolite on the crystallization behavior, spherulite growth and crystal structure of PLA were investigated by means of differential scanning calorimetry (DSC), polarized optical microscope (POM), wide angle X‐ray diffraction (WAXD), Fourier transform infrared (FTIR), and scanning election microscope (SEM). On the basis of DSC and POM results, the overall crystallization kinetics of PLA/sepiolite nanocomposites were significantly enhanced leading to higher crystallinity and nucleation density, faster spherulite growth rate (G) and lower crystallization half‐time (t_1/2) compared with the neat PLA. Under non‐isothermal conditions, the PLA blend comprising 1.0 wt% of sepiolite still revealed two crystallization peaks upon cooling at a rate of 35°C/min. Above phenomena strongly suggested that sepiolite was an effective nucleating agent for PLA. FTIR and WAXD analyses confirmed that the crystal structure of PLA matrix was the most common α‐form. SEM micrographics illustrated the fine three‐dimensional spherulite structures with the lath‐shape lamellae regularly arranged in radial directions. POLYM. ENG. SCI., 55:1104–1112, 2015. © 2014 Society of Plastics Engineers     

Effect of silicon dioxide on crystallization and melting behavior of polypropylene

The crystallization and melting behavior of isotactic polypropylene (iPP) and polypropylene copolymer (co‐PP) containing silicon dioxide (SiO₂) were investigated by differential scanning calorimeter (DSC). SiO₂ had a heterogenous nucleating effect on iPP, leading to a moderate increase in the crystallization temperature and a decrease in the half crystallization time. However, SiO₂ decreased the crystallization temperature and prolonged the half crystallization time of co‐PP. A modified Avrami theory was successfully used to well describe the early stages of nonisothermal crystallization of iPP, co‐PP, and their composites. SiO₂ exhibited high nucleation activity for iPP, but showed little nucleation activity for co‐PP and even restrained nucleation. The iPP/SiO₂ composite had higher activation energy of crystal growth than iPP, indicating the difficulty of crystal growth of the composite. The co‐PP/SiO₂ composite had lower activation energy than co‐PP, indicating the ease of crystal growth of the composite. Crystallization rates of iPP, co‐PP, and their composites depended on the nucleation. Because of its high rate of nucleation, the iPP/SiO₂ composite had higher crystallization rate than iPP. Because of its low rate of nucleation, the co‐PP/SiO₂ composite had lower crystallization rate than co‐PP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1889–1898, 2006     

Ultrasound assisted continuous‐mixing for the preparation of PP/SEBS/OMMT ternary nanocomposites

Polypropylene (PP)/polystyrene‐block‐poly(ethylene‐co‐butylenes)‐block‐polystyrene (SEBS)/organo‐montmorillonite (OMMT) nanocomposites of varying concentrations of maleic anhydride‐grafted polypropylene (PP‐g‐MA) were prepared by continuous mixing assisted by ultrasonic oscillation. The structure and morphology of nanocomposites were investigated by X‐ray diffraction (XRD), transmission electron microscopy, and scanning electron microscopy. It was found that both PP‐g‐MA and ultrasonic oscillation could enhance the intercalation and exfoliation of OMMT in PP matrix. Meanwhile, the formation of PP could be induced by ultrasonic irradiation at a power of more than 540 W. Rheological properties including complex viscosity, storage, and loss modulus of nanocomposites were increased after adding PP‐g‐MA or ultrasonic treatment. The results of mechanical properties showed that PP‐g‐MA could improve the tensile strength and tensile modulus of nanocomposites, but with the sacrifice of impact strength. This problem could be improved by ultrasound due to the reduced particle size of SEBS. However, the mechanical properties would be reduced by ultrasonic treatment with higher intensity due to the polymer degradation. Therefore, the synergistic effect of both compatibilizer and ultrasound should account for the balance between toughness and stiffness of PP/SEBS/OMMT ternary nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41202.