Effect of final heating temperature on crystallization of isotactic polypropylene nucleated with an aryl amide derivative as <Emphasis Type="Italic">β</Emphasis>-form nucleating agent

An aryl dicarboxylic acid amide compound TMB-5 is an efficientβ-form nucleating agent for isotactic polypropylene(iPP).Because of the solubility of TMB-5,superstructure and morphology of iPP crystals changed with melting conditions.Effects of final heating temperature(T_f)on heterogeneous nucleation of iPP/TMB-5 were investigated.It was discovered that the crystallization temperature increased with decreasing T_f value.The optical microscopic images indicated that when TMB-5 partially dissolved in iPP melt,the remaining(non-dissolved)TMB-5 facilitated the recrystallization of dissolved nucleating agent from the melt,which promoted crystallization.Complete solubility of nucleating agent caused the decreasing efficiency.TMB-5 recrystallized in the form of tiny needles,whose aggregates induced dendritic iPP crystals.     

Temperature-dependent β-Crystal Growth in Isotactic Polypropylene with β-Nucleating Agent after Shear Flow

In our current work, the effect of the shear temperature on the growth of β-crystal in isotactic polypropylene(iPP) with β-nucleating agent is investigated by means of in situ two-dimensional wide-angle X-ray diffraction(2 D-WAXD). At low shear temperatures, the formed shear-induced oriented precursors are hard to relax back to random coiled state due to the weak mobility of molecular chains. Therefore, plenty of oriented α-crystals are induced by shear-induced oriented precursors, while β-crystal is greatly depressed. As the shear temperature increases, oriented β-crystal gradually increases along with the decrease of α-crystal. It is deduced that the shear temperature at which the content of β-crystal increases to the(maximum) value found in quiescent crystallization is almost the same as that at which the accelerating effect of flow on crystallization kinetics is completely erased. Our work manifests its significance in regulating β-crystal and thus in the structure and property manipulation of i PP.     

Self-nucleation Effect of Crystallization with Various Nucleating Agents

In this work, the self-nucleation effect on crystallization was studied for polypropylene with various nucleating agents. The talc was employed to accelerate crystallization of monoclinic α-crystallites, while N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide TMB-5 was used to accelerate the crystallization kinetics and also induce formation of trigonal β-crystallites. To induce self-nucleation effect, the occurrence criterion was assessed by the transition temperatures from various domains and the...     

Direct Comparison of Crystal Nucleation Activity of PCL on Patterned Substrates

A sample containing different regions with poly(ε-caprolactone)(PCL), oriented polyethylene (PE), and oriented isotactic polypropylene (iPP) films in contact with glass slide has been prepared to be observed in the same view field in an optical microscope and the crystallization of PCL in different regions during cooling from 80 °C down to room temperature at a rate of 1 °C·min^-1 was studied. The results showed that the crystallization of PCL started first at the PE surface and then at the iPP surface, while its bulk crystallization occured much later. This indicates that though both PE and iPP are active in nucleating PCL, the nucleation ability of PE is stronger than that of iPP. This was due to a better lattice matching between PCL and PE than that between PCL and iPP. Moreover, since lattice matching existed between every (hk0) lattice planes of both PCL and PE but only between the (100)PCL and (010)iPP lattice planes, the uniaxial orientation feature of the used PE and iPP films resulted in the existence of much more active nucleation sites of PCL on PE than on iPP. This led to the fact that the nucleation density of PCL at PE surface was so high that the crystallization of PCL at PE surface took place in a way like the film developing process with PCL microcrystallites happened everywhere with crystallization proceeding simultaneously. On the other hand, even though iPP also enhanced the nucleation density of PCL evidently, the crystallization of PCL at iPP surface included still a nucleation and crystal growth processes similar to that of its bulk crystallization.     

Combined effect of modified zeolite 13X and β-nucleating agent on improving β-crystal content and toughening polypropylene random copolymer

Although addition of β-NUCLEATING agent directly into homo-polypropylene(PPH) is a useful method to improve β-CRYSTAL content and toughen PPH, polypropylene random copolymer(PPR) makes this method powerless due to its random structure and low crystallinity. In this study, the-nucleated PPR with high β-CRYSTAL content was prepared by a novel high effective β-NUCLEATING system which consists of-nucleation agent(TMB-5) and modified zeolite 13X(M13X). It was found that M13X and TMB-5 had a synergistic influence on improving β-CRYSTAL content and toughening PPR. The content of β-CRYSTAL in PPR/M13X/TMB-5 was significantly larger than the sum of that in PPR/M13X and PPR/TMB-5. Besides,fracture behavior, phase morphology and relaxation of matrix chain segments were also investigated. The results showed that M13X and TMB-5 improved the mobility of amorphous chain segments at low temperature and contributed to much energy dissipation. This work provides a powerful method to modify PPR.     

Crystallization behavior and morphology of one-step reaction compatibilized microfibrillar reinforced isotactic polypropylene/poly(ethylene terephthalate) (<Emphasis Type="Italic">i</Emphasis>PP/PET) blends

One-step reaction compatibilized microfibrillar reinforced iPP/PET blends(CMRB) were successfully prepared through a "slit extrusion-hot stretching-quenching" process.Crystallization behavior and morphology of CMRB were systematically investigated.Scanning electronic microscopy(SEM) observations showed blurry interface of compatibilized common blend(CCB).The crystallization behavior of neat iPP,CCB,microfibrillar reinforced iPP/PET blend(MRB) and CMRB was investigated by differential scanning calorimetry(DSC) and polarized optical microscopy(POM).The increase of crystallization temperature and crystallization rate during nonisothermal crystallization process indicated both PET particles and microfibrils could serve as nucleating agents and PET microfibrils exhibited higher heterogeneous nucleation ability,which were also vividly revealed by results of POM.Compared with MRB sample,CMRB sample has lower crystallization temperature due to existence of PET microfibrils with smaller aspect ratio and wider distribution.In addition, since in situ compatibilizer tends to stay in the interphase,it could also hinder the diffusion of iPP molecules to the surface of PET phase,leading to decrease of crystallization rate.Two-dimensional wide-angle X-ray diffraction(2D-WAXD) was preformed to characterize the crystalline structure of the samples by injection molding,and it was found that well-developed PET microfibrils contained in MRB sample promoted formation ofβ-phase of iPP.     

MULTIPLE MELTING BEHAVIOR OF β-CRYSTALLINE PHASE POLYPROPYLENE

Differential scanning calorimetry and X-ray diffraction experiments on β-nucleated polypropylene were made on the samples crystallized at different temperatures and processed by injection molding. The crystal perfection was shown to vary with crystallization temperature. The observed multiple peaks could be related to a ill-phase with defective inclination of the chains, a recrystallized or original β_2-phase of more perfect inclination, and the α-phase. Injection molded samples could be analyzed from the established DSC interpretation.     

Enhanced Crystallization Rate of Biodegradable Poly(ε-caprolactone) by Cyanuric Acid as an Efficient Nucleating Agent

The influence of cyanuric acid(CA) as an efficient nucleating agent on the crystallization behavior and morphology of biodegradable poly(ε-caprolactone)(PCL) was extensively studied in this work with several techniques for the first time. The nonisothermal melt crystallization behavior and overall isothermal melt crystallization rate of PCL were significantly enhanced by only a small amount of CA. The addition of CA apparently improved the nonisothermal melt crystallization peak temperature, overall isothermal melt crystallization rate, and nucleation density of PCL spherulites, but did not modify the crystallization mechanism and crystal structure of PCL, indicating that CA was an efficient nucleating agent for the crystallization of PCL. The possible nucleation mechanism of CA on the crystallization of PCL was also discussed on the basis of their crystal structures.     

Effects of crystallization temperature and blend ratio on the crystal structure of poly(butylene adipate) in the poly(butylene adipate)/poly(butylene succinate) blends

The effects of crystallization temperature and blend ratio on the polymorphic crystal structures of poly(butylene adipate)(PBA) in poly(butylene succinate)(PBS)/poly(butylene adipate)(PBS/PBA) blends were studied by means of differential scanning calorimetry(DSC), wide-angle X-ray diffraction(XRD) and atomic force microscopy(AFM). It was revealed that the polymorphism of PBA can be regulated by the blend ratio even in a non-isothermal crystallization process. The results demonstrate that high temperature favors flat-on α crystals, while low temperature contributes to edge-on β crystals. It was also found that the effect of blend ratio on the crystallization mechanism of PBA is well coincident with that of the crystallization temperature. The increment of PBS content in the PBS/PBA blend gives rise to more β-form crystals of PBA. For those PBS/PBA blends with low PBA content, the interlamellar phase segregation of PBA makes its molecular chains so difficult to diffuse from one isolated microdomain to another that high crystallization temperature and sufficiently long crystallization time will be required if the PBA α-type crystals are targeted.     

β-PHASE CRYSTALLIZATION OF ISOTACTIC POLYPROPYLENE

Effects of cooling rate and crystallization and melt temperatures on the melting curves of predomi-nately β-phase isotactic polypropylene (IPP) were investigated by using DSC instrument. Experimental re-sults indicate that the magnitude of βmelting endctherm increases with decreasing cooling rate and withincreasing crystallization temperature. The temperature of melt has no effect on the β-phase crystallizationof IPP below 300℃, but a further increase of the melt temperature will destroy the β-phase nuclei,then the β-phase crystals will not be produced upon cooling. The linear growth rates of α- and β-phasespherulites were determined as a function of temperature between 123 and 140℃. It was found that thegrowth rate of βspherulites is higher than that of αspherulites below 140℃. Studies of the kinetics ofβ-phase crystallization of IPP were also made using a DSC instrument. The results obtained do not fitthe usual Avrami equation. But it can be described by kinetic theory of imcomplete spher     

Investigation on structural changes of isotactic polypropylene mesophase in the heating process by using two-dimensional infrared correlation spectroscopy

Two-dimensional FT-IR correlation spectroscopy was used to reveal the structural changes of isotactic polypropylene(iPP) mesophase during the heating process.The co-relationship among the regular helical bands of iPP was discussed according to synchronous spectrum.The results show that the segments with different length-helixes were found to undergo a disordered process in the temperature range of 25-60 ℃.     

Helical secondary structures and supramolecular tilted chirality in N-terminal aryl amino acids with diversified optical activities

Helix structures at atomic/molecular level have not been found in self-assembled peptide seque nce with less than three residues.As β-sheet supramolecular secondary structures have been discovered in solidstate amino acids,we here report the conjugation of simple N-terminal aryl protecting group could give rise to helical supramolecular secondary structures in solid-state,which determines the optical activities of the adjacent aryl groups.The carboxylic acid-involved asymmetric H-bonds in N-te rminal aryl amino acids induce the emergence of super-helical structures of amino acid residues and aryl groups.In most cases,supramolecular tilted chirality of aryl groups is opposite to that of amino acid sequences,of which handedness and helical pitch are determined by the H-bond modalities.Determining correlation between supramolecular tilted chirality of aryl segments and their chiroptical activities is firstly unveiled,which was verified by the computational results based on density functional theory.Most aryl amino acids self-assembled by nanoprecipitation method via crystallization induced self-assembly into rigid one-dimensional microstructures with ultra-high Young's modulus.This study reveals the generic existence of chiral supramolecular structure s in aggregated amino acid derivatives and gives an in-depth investigation into the structural-property relationships,which could guide the rational design and screening of chiroptical supramolecular materials.     

Influence of Teflon Substrate on Crystallization and Enzymatic Degradation of Polymorphic Poly（butylene adipate）

Oriented and non-oriented Teflon films, which were found to have the same crystalline structure, but different surface morphologies, were used to sandwich poly(butylene adipate)(PBA) films during isothermal crystallization. It was found that both the Teflon surface structure and the PBA polymorphic structure are the determining factors to induce epitaxial crystallization. The oriented Teflon film was able to induce epitaxial crystallization of PBA α crystal, while the non-oriented Teflon did not induce any epitaxial crystallization of PBA. Epitaxial crystallization did not occurred for PBA β crystals between neither the oriented nor the non-oriented Teflon films. The enzymatic degradation rate of PBA films was not determined by the epitaxial crystallization, in fact it was still dependent on the polymorphic crystal structure of PBA. The morphological changes of PBA films after enzymatic degradation confirmed again that the epitaxial crystallization only occurred for the PBA film with α crystal structure which was produced by being sandwiched between oriented Teflon films, and it happened only on the surface of PBA films.     

New understanding on the memory effect of crystallized iPP

In this study, recovery processes of isotactic polypropylene(iPP) melted spherulites at 135 °C after melting at higher temperatures(170 °C–176 °C) were investigated with polarized optical microscopy and Fourier transform infrared spectroscopy. The recovery temperature was fixed to exclude the interference from heterogeneous nuclei. After melting at temperatures between 170 °C and 174 °C, the melted spherulite could recover back to the origin spherulite at low temperatures. Interestingly, a distinct infrared spectrum from iPP melt and crystal was observed in the early stage of recovery process after melting at low temperatures, where only IR bands resulting from short helices with 12 monomers or less can be seen, which indicates that the presence of crystal residues is not the necessary condition for the polymer memory effect. Avrami analysis further indicated that crystallization mainly took place in melted lamellae. After melting at higher temperatures, melted spherulite cannot recover. Based on above findings, it is proposed that the memory effect can be mainly ascribed to melted lamellae, during which crystalline order is lost but conformational order still exists. These conformational ordered segments formed aggregates, which can play as nucleation precursors at low temperatures.     

Crystallization kinetics and morphology of poly(vinylidene fluoride)/poly(ethylene adipate) blends

The miscibility, isothermal crystallization kinetics and morphology of the poly(vinylidene fluoride)(PVDF)/poly(ethylene adipate)(PEA) blends have been studied by differential scanning calorimetry(DSC), optical microscopy(OM) and scanning electron microscopy(SEM). A depression of the equilibrium melting point of PVDF was observed. From the melting point data of PVDF, a negative but quite small value of the interaction parameter ?PVDF-PEA is derived using the Flory-Huggins equation, implying that PVDF shows miscibility with PEA to some extent. Nonisothermal and isothermal crystallization kinetics suggest that the crystallization rate of PVDF decreases with increasing the amount of PEA, and a contrary trend was found when PEA crystallizes with the increase of the amount of PVDF. It was further disclosed that the blend ratio and crystallization temperature affect the texture of PVDF spherulites greatly, which determines the subsequent crystallization of PEA. At high temperatures, e.g. 150 ℃, the band spacing of PVDF spherulites increases with the addition of PEA content and the spherulitic structure becomes more open. In this case, spherulitic crystallization of PEA is not observed for all blend compositions. At low temperatures, e.g. 130 ℃, for the PEA-rich blends, the interpenetrated structures are eventually formed by the penetration of the spherulites of PEA growing within the pre-existing PVDF spherulites.     

Structure and Properties of β-Polypropylene Reinforced by Polypropylene Fiber and Polyamide Fiber

Matrix/fiber composites of β-form isotactic polypropylene(iPP) matrix and α-iPP or PA6 fibers were prepared by laminating technique under different preparation temperatures. The mechanical properties and interfacial morphologies of these composites were studied by tensile test, optical microscopy and scanning electron microscopy, respectively. The experimental results show that the tensile yield load and tensile modulus of β-iPP/PA6 matrix/fiber systems increased significantly at the expense of elongation at break. These mechanical properties show essentially no dependence on the sample preparation temperature. On the other hand, the mechanical properties of iPP matrix/fiber single polymer composites depend strongly on the sample preparation temperature. At low sample preparation temperature, e.g., 172 ℃, the solid α-iPP fiber induces α-iPP crystallization, leading to the formation of α-iPP transcrystalline layer around the fiber. This results in a remarkable increment of the tensile yield load and tensile modulus. The elongation at break is also much better than that of the iPP/PA6 matrix/fiber system. It reflects a better interfacial adhesion of the single polymer composite compared with the iPP/PA6 composite. At higher sample preparation temperature, e.g., 174 ℃ or 176 ℃, the partial surface melting of the oriented fiber allows interdiffusion of iPP molecular chains in the molten fiber and matrix melt. The penetration of matrix chains into the molten iPP fiber results in some iPP molecular chains being included partially in the recrystallized fiber and the induced β-transcrystalline layers. This kind of configuration leads to an improvement of interfacial adhesion between the fiber and matrix, which causes a simultaneous increase of the tensile yield load, tensile modulus and elongation at break of β-iPP.     

Overshoots in stress and free energy change during the flow-induced crystallization of polymeric melt in shear flow

<正>The effect of pre-shear flow on the subsequent crystallization process of polymeric melt was investigated and a flow-induced crystallization(FIC) model based on the conformation tensor incorporating the pre-shear effect was proposed. The model is capable of predicting the overshoot phenomena of the stress and the flow-induced free energy change of the polymeric system at high pre-shear rates.Under the condition of flow,the increase in the activated nuclei number was contributed by the flow-induced free energy change,which showed an overwhelming effect on the nuclei formation during the pre-shear process at high shear rates.The half crystallization time(f_(1/2)) of polypropylene(PP) as functions of pre-shear rate and pre-shear time at different crystallization temperatures was predicted and compared with the experiment data.Both numerical and experimental results showed that t_(1/2) of PP decreased dramatically when the flow started but leveled off at long times.It was found that two transformation stages in t_(1/2) existed within a wide range of shear rates.For the first stage where the melting polymer experienced a relatively weak shear flow,the acceleration of crystallization kinetics was mainly contributed by the steady value of free energy change while in the second stage for high shear rates,strong overshoot in flow-induced free energy change occurred and the crystallization kinetics was thus significantly enhanced.The overshoots in stress and flow-induced free energy change reflected an important role of flow on the primary nucleation especially when the flow was strong enough.     

Formation of Poly（L-lactide） Mesophase and Its Chain Mobility Dependent Kinetics

In the present work, the PLLA mesophase formation and its kinetics at the advent of a chain mobility accelerator （polyethylene glycol （PEG）） are investigated by wide angle X-ray diffraction （WAXD） and time-resolved Fourier transform infrared spectroscopy （FTIR）. It is interestingly found that the presence of PEG could accelerate the formation of PLLA mesophase notably due to the enhanced chain mobility, giving rise to a substantially reduced half time （t0.5） of PLLA mesophase formation from 129 min to 8 min. The Avrami exponents （n） for the kinetics of mesophase formation are -0.5 for neat PLLA and 1 for PLLA/PEG, respectively, indicating that 1D-rod growth through heterogeneous nucleation occurs during formation of PLLA mesophase. Tensile testing demonstrates that PLLA mesophase could increase the tensile strength and modulus but decrease the elongation at break.     

Synthesis,Characterization and Application of Methyl 3,5-Disulfo-benzoate Dipotassium Dihydrate as Nucleating Agent for Poly（L-lactide）

A newly synthesized aromatic sulfonate compound,complex 2 with formula of K2[H3COOC-C6H3（SO3）2]·2H2O（methyl 3,5-disulfo-benzoate dipotassium dihydrate） was synthesized and characterized by elemental analysis,infrared（IR） spectrometry,nuclear magnetic resonance（NMR） and crystal structure measurement.Single-crystal X-ray diffraction（XRD） revealed that complex 2 crystallized in the triclinic system with space group P（i）.Complex 2 was used as nucleating agent for poly（L-lactide）（PLLA）.The crystallization of PLLA with powder of complex 2 was investigated by means of differential scanning calorimetry（DSC） and polarized optical microscopy （POM）.The results prove that complex 2 was effective as nucleating agent for PLLA.It could accelerate crystallization by reducing the induction time and increasing the density of nuclei in the crystallization process.The half-time of crystallization（t0.5） for pure PLLA was about 8 times longer than that of PLLA sample with 1.0％（mass fraction） of complex 2.     

Preparation of Zeolite X Membranes on Porous Ceramic Substrates with Zeolite Seeds

Zeolite X membranes were investigated by in-situ hydrothermal synthesis on porous ceramic tubes precoated with zeolite X seeds or precursor amorphous aluminosilicate, and porous α-Al2O3 ceramic tubes with a pore size of 50-200 nm were employed as supports. Zeolite X crystals were synthesized by the classic method and mixed into deionized water as a slurry with a concentration of 0.2-0.5wt%, having a range of crystal sizes from 0.2 to 2μm. Crystal seeds were pressed into the pores near the inner surface of the ceramic tubes, and crystallization took place at 95℃ for 24-96 h. It was also investigated that Boehmite sol added with zeolite X seeds was precoated on ceramic supports to form a layer of r-Al2O3 by heating, and hydrothermal crystallization could then take place to prepare the zeolite membranes on the composite ceramic tubes. The crystal species were characterized by XRD, and the morphology of the supports subjected to crystallization was characterized by SEM. The composite zeolite membranes hav