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In this paper, we used neopentyl glycol as a comonomer to participate in the reaction with poly(ethylene terephthalate), and synthesized poly(ethylene terephthalate-co-neopentyl glycol) polyester samples. Through a series of tests, we found that the crystallization ability of the copolymer is closely related to the content of comonomer. Self-nucleation and annealing thermal fractionation were first used to study copolymer, as well as non-isothermal crystallization kinetics analysis were also employed to estimate how neopentyl glycol contents affected the crystallization ability of copolymer. With the increase of neopentyl glycol content, the crystallinity, crystalline rate, Avrami exponent of copolymer changed obviously. Besides, X‑ray diffraction was also used to study the crystalline structures of samples. Results showed that the crystalline of the copolymer have not been changed by the variety of neopentyl glycol content. [ABSTRACT FROM AUTHOR]

Poly-L-lactic acid (PLLA) is an environmentally friendly and renewable polymer material with excellent prospects, but its low crystallization rate greatly limits its application. Through the amidation reaction between amino hyperbranched polymer (HBP N103) and carboxylated carbon nanotubes (CNTs), CNTs-N103 was obtained. The modification was confirmed by Fourier-transform infrared (FTIR) spectroscopy, X-ray electron spectroscopy (XPS) and thermogravimetric analysis (TGA). Using transmission electron microscopy (TEM), we observed the changes on the surface of modified CNTs. PLLA/CNT composites were prepared, and differential scanning calorimetry (DSC) was used to investigate the crystallization behavior of the composites. The results showed that the addition of CNTs could greatly improve the crystallization properties of PLLA; at the same concentration, the modified CNTs had better regulation ability in PLLA crystallization than the unmodified CNTs. Moreover, in the concentration range of 0.1–1%, with the increase in HBP concentration, the ability of CNTs-N103 to regulate the crystallization of PLLA increased as well. Wide-angle X-ray diffraction (WAXD) once again proved the improvement of the crystallization ability. The results of polarized optical microscopy (PLOM) showed that the number of nucleation points increased and the crystal became smaller. [ABSTRACT FROM AUTHOR]

In order to explore the effect of molecular structure on the crystallization and polymorphic behavior of β-nucleated isotactic polypropylene (β-iPP), four commercial iPP samples with different average isotacticities, molecular weights and isotactic distributions were used. The relationship between the molecular structure characteristics and β-crystallization behavior were investigated by means of xylene solvent fractionation (XS), successive self-nucleation and annealing fractionation (SSA), carbon-13 nuclear magnetic resonance spectrometry (13C NMR), gel permeation chromatography (GPC), melt index (MI) and differential scanning calorimetry (DSC). Results of molecular structure characterization revealed that their isotacticity can be ranged as F401 > 5014L > F03G ≈ T38F, while the order of their isotactic distribution width is 5014L ≈ T38F > F401 ≈ F03G. Results of crystallization kinetics revealed that the molecular weight of the samples has little effect on their crystallization and polymorphic behavior. Meanwhile, crystallization activation energy Ec can be ranged as 5014L < F401 < F03G < T38F, indicating that when the molecular weight was above a certain degree, the isotacticity is the main factor affecting the crystallization ability of β-type iPP (β-iPP). The higher the isotacticity and the wider the distribution is, the stronger the β-crystallization ability is. Moreover, the β-crystallization ability of the samples is closely related to the isotacticity of the sample, which can be effectively controlled by tuning the fraction of high isotacticity with high molecular weight components. [ABSTRACT FROM AUTHOR]

In this study, we have prepared two β‐nucleated isotactic polypropylene/graphene oxide (β‐iPP/GO) composites with different stereo‐defect distribution (named NPP‐B and NPP‐A). The role of stereo‐defect distribution on the crystallization and polymorphic behaviors of samples with varied melt structures were investigated by scanning electron microscopy (SEM), wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC). It was found that NPP‐B (who with more uniform stereo‐defect distribution) prefers β‐crystallization; while NPP‐A has a strong α‐nucleation tendency and can hardly form β‐phase; as fusion temperature decreases from 200°C to 168°C, the relative percentages of β‐phase of NPP‐B and NPP‐A exhibit the same trends, suggesting that the β‐nucleation efficiency is enhanced by the ordered structure effect (OSE) and causes β‐crystallization even in NPP‐A. Moreover, the lower limiting temperatures of Region‐II of NPP‐B and NPP‐A are the same but their upper limiting temperatures are different, indicating the uniformity of stereo‐defect distribution also influences temperature window for OSE. Related mechanisms were discussed. POLYM. ENG. SCI., 59:1097–1104 2019. © 2019 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

In this paper, effects of ordered structure on non-isothermal crystallization kinetics and subsequent melting behavior of β-nucleated isotactic polypropylene/graphene oxide composites were investigated. Under all cooling rates, as fusion temperature Tf stepped into the range of 168–178 °C, the ordered structure survived in the melt, resulting in the increase in crystallization peak temperature Tp, the decrease in crystallization activation energy ΔE and the decrease in the half crystallization time t1/2. When endset temperature of cooling Tend = 50 °C, lower cooling rate encouraged the formation of more β-phase. Moreover, the influence of ordered structure on β-α recrystallization was studied by adjusting the Tend. When Tend = 105 °C, higher cooling rate encouraged the formation of more β-phase. The ordered structure was favorable for the improvement of the thermal stability of the β-phase during β-α recrystallization. [ABSTRACT FROM AUTHOR]

Abstract: The effects of ordered structure on isothermal crystallization kinetics and subsequent melting behavior of β‐nucleated isotactic polypropylene/graphene oxide (iPP/GO) composites were studied using differential scanning calorimetry. The ordered structure status was controlled by tuning the fusion temperature (Tf). The results showed that depending on the variation of crystallization rate, the whole Tf range could be divided into three regions: Region I (Tf > 179 °C), Region II (170 °C ≤ Tf ≤ 179 °C) and Region III (Tf < 170 °C). As Tf decreased from Region I to Region III, the crystallization rate would increase substantially at two transition points, due to the variation of the ordered structure status. Calculation of Avrami exponent n indicated that the ordered structure induced the formation of two‐dimensional growing crystallites rather than three‐dimensional growing crystallites. Moreover, in the case of isothermal crystallization, the ordered structure effect (OSE) can also greatly increase the relative content of β‐phase (βc). In Region II, OSE took place, resulting in evident increase of βc, achieving 92.4% at maximum. The variation of the isothermal crystallization temperature (Tiso) had little influence on the Tf range (Region II) of the OSE. The higher Tf in Region II was more favorable for the formation of higher βc. The ordered structure was favorable for the improvement of the nucleating efficiency of β‐nucleating agent (β‐NE), and was more effective for the improvement of lower β‐NE. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

To investigate effects of molecular structures on β-crystallization of polypropylene random copolymer (PPR), PPR-A and PPR-B with similar molecular weight and distribution but significantly different polymorphic behavior were used. Wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FT-IR), solvent fractionation combined with successive self-nucleation and annealing (SSA) and Gel Permeation Chromatography (GPC) were applied. Results revealed that after addition of same amount of β-nucleating agent (β-NA), large amount of β-phase is obtained in PPR-A ( K = 0.603), while no β-phase can be seen from PPR-B; Structure characterizations revealed that they have similar molecular weight but different total amount and distribution of ethylene comonomer: the total content of ethylene comonomer of PPR-A is higher compared with PPR-B, but its ethylene comonomer distribution is less uniform. In this way, PPR-A possesses high molecular weight high isotactic fraction, which cannot be seen from PPR-B due to its more uniform comonomer distribution. Therefore, the presence of highly isotactic PP (HPP) is the key factor in β-crystallization of PPR. For verification, HPP with low or high molecular weights are respectively added into β-nucleated PPR-B. Results revealed that HPP was effective in enhancing β-crystallization of PPR-B; higher molecular weight of HPP was more favorable and more effective. [ABSTRACT FROM AUTHOR]

In this study, polyethylene glycol (PEG) of different molecular weight was added into poly(vinylidene fluoride) (PVDF) through melt blending. The hydrophilicity, processability, mechanical properties of the blends were investigated. Moreover, to understand fully, the crystallization and melting behavior, crystalline structure, molecular interactions of the blends were also studied. Results revealed that the addition of PEG evidently enhances the ductile and reduces the rheological torque of PVDF, what's more, the contact angle of the blends with water was greatly reduced. The solid surface tension γ, chromatic dispersion part γ and polar part γ suggested the surface tension of the blend gradually increased from 38.31 to 55.65 mJ/m with the increase of PEG-20000 content.Wherein the dispersion part of the tension changed little, the polar part of the tension increased significantly from 5.74 to 20.41 mJ/m, indicating that the addition of PEG greatly enhanced the polar part of surface tension of the blend, and therefore evidently enlarged the hydrophilic property of the blends. Besides, to elucidate the related effecting mechanism, the crystallization and molecular interaction of the blends were also studied. [ABSTRACT FROM AUTHOR]

In this study, the effects of melt structure (tuned by controlling the fusion temperature Tf) on non-isothermal crystallization and subsequent melting behaviors of isotactic polypropylene (iPP) nucleated with α/β compounded nucleating agents (α/β-CNAs) have been further investigated. The results show that under all cooling rates studied (2-40°C/min), the crystallization temperature on cooling curves increased gradually with decrease of Tf, meanwhile, when Tf was in temperature range of 166°C-179°C where ordered structures survived in the melt (defined as Region II), crystallization activation energy ΔE was found to be evidently lower compared with that when Tf > 179°C or Tf < 166°C. The results of subsequent heating showed that occurrence of Ordered Structure Effect can be observed at all the cooling rates studied; the location of the Region II was constant when cooling rate varied; Low cooling rate encouraged formation of more β-phase triggered by ordered structure. Moreover, the role of ordered structure on β-α recrystallization was comparatively studied by tuning the end temperature of recooling ( Tend) after held at Tf, and it was found that ordered structure encouraged the formation of β-phase with high thermal stability at low temperature part of Region II, while enhanced the β-crystal with relatively low thermal stability at high temperature part of Region II. POLYM. ENG. SCI., 57:989-997, 2017. © 2016 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Previous studies reported that by tuning the fusion temperature T (i.e., controlling the melt structure), the β-nucleation efficiency of β-nucleated isotactic polypropylene (β-iPP) can be greatly enhanced, which was called ordered structure effect (OSE). The aim of this study is to investigate the roles of melt structures and molecular weight in non-isothermal crystallization behavior of β-iPP. Five samples with different molecular weights were prepared, and their melt structures were controlled using differential scanning calorimetry (DSC) by tuning T ( T = 200 or 170 °C represent the case of without or with OSE, respectively). Results revealed that for all the samples, the lower the PP molecular weight, the lower the crystallization peak temperature T , and the higher the activation energy Δ E, but the occurrence of OSE behavior (i.e., T = 170 °C) can elevate T , reduces Δ E and encourages crystallization. The decrease of PP molecular weight decreases β-phase proportion no matter OSE occurs or not; moreover, for PP with high molecular weight, OSE behavior not only enhances the β-phase proportion, but also increases the thermal stability of the β-phase; however, for samples with low molecular weight, OSE behavior enhances the β-phase proportion in a larger extent, and decreases the thermal stability of the β-phase. This study provided important understandings in the effect of OSE, cooling rate and PP molecular weight the β-crystallization of iPP. [ABSTRACT FROM AUTHOR]

The β-nucleated isotactic polypropylene (β-iPP)/isotactic poly(4-methylpentene-1) (TPX) composites were prepared using a β-nucleating agent (TMB-5). The crystallization behavior and polymorphic morphology of β-iPP with various concentration of TPX were investigated by differential scanning calorimetry, wide-angle X-ray diffraction, and scanning electronic microscopy. The results showed that the addition of TPX increases the content and the spherulite sizes of β-phase but decreases the crystallization temperature and reduces the crystallization energy barriers as well. For melting behavior, it was found that the β-phase content of samples greatly depend on the cooling rate applied and the appearance of TPX. [ABSTRACT FROM AUTHOR]

The influence of bi-component β-nucleating agent of pimelic acid/calcium stearate (Pa-Cast) on the non-isothermal crystallization behavior and polymorphic composition of two isotactic polypropylene (iPP) samples with nearly same average isotacticity but different uniformities of stereo-defect distribution were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and Scanning electronic microscopy (SEM). The results indicated that Pa-Cast has very high β-nucleation efficiency, and greatly increases the crystallization rate of both samples. After the addition of Pa-Cast, the sample with more uniform distribution of stereo-defect and less fraction of high isotacticity (denoted as PCPP-B) is more favorable for formation of large amount of β-phase; meanwhile, its increase of crystallization peak temperature T is obviously more prominent. Further analysis of melting behavior showed that the β-phase content greatly depends on the cooling rate applied, the stereo-defect distribution of iPP and the end temperature of cooling ( T). When T = 50 °C, for iPP with less uniform stereo-defect distribution (PCPP-A), the slow cooling rate favors the formation of high β-content, while for PCPP-B, the fast cooling rate favors the formation of high β-content, which should be attributed to the combination effect of the ability for β-crystallization and the thermal stability of the β-phase. After elimination of the confusion of β-α recrystallization during heating ( T = 100 °C), it turns out that for both PCPP-A and PCPP-B, higher cooling rate is more favorable for β-crystallization. PCPP-A is more favorable for the formation of β-phase with higher thermal stability compared with PCPP-B. [ABSTRACT FROM AUTHOR]

ABSTRACT 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 [ABSTRACT FROM AUTHOR]

To elucidate the synergetic effect in enhancing β-crystallization between β-nucleating agent (β-NA) and ordered structures of isotactic polypropylene (iPP), i.e., ordered structure effect (OSE), in this study, the role of β-NA concentration (C) was studied by differential scanning calorimetry (DSC) and in-situ small-angle X-ray scattering (in-situ SAXS). Results showed that C was a determining factor of OSE: C < 0.01 wt% was too low to induce β-crystallization while C ≥ 0.09 wt% was saturated β-NA concentration, and none of them can induce OSE; only when C = 0.01-0.08 wt% (i.e., unsaturated concentration) can OSE take place. There existed a competitive relationship in the enhancement of β-phase between OSE and conventional β-nucleation effect of β-NA. Moreover, in-situ SAXS revealed that at T = 190 °C (around upper limiting temperature for occurrence of OSE), when C was different, the geometric shapes of ordered structures in iPP melts were quite different from each other. The involved mechanism was proposed. [ABSTRACT FROM AUTHOR]

The melt structure of isotactic polypropylene (iPP) nucleated with 1.0 mass% multi-walled carbon nanotubes (CNTs) and 0.05 mass% rare earth β-phase nucleating agent (WBG-II) was tuned by changing the fusion temperature T. In this way, the role of melt structure in the crystallization behavior and polymorphic composition of the sample was studied by calorimetry, X-ray diffraction, and scanning electronic microscopy. In this system, the sample cannot form any β-phase when T = 200 °C, since the α-nucleation efficiency (α-NE) of CNTs was obviously higher than the β-NE of WBG-II. By tuning T, the content of ordered structures in iPP melt was controlled and it was found that the polymorphic composition of the sample can be efficiently controlled. When T was in the range of 166-174 °C, an amount of ordered structures survived in iPP melt, resulting in a significant increase of β-phase proportion; moreover, study on the crystallization behaviors of single CNTs-filled iPP and WBG-II-nucleated iPP (iPP/CNTs and iPP/WBG-II, respectively) revealed that the α-NE of iPP/CNTs stayed almost constant as T varies from 200 to 166 °C; meanwhile, the β-NE of iPP/WBG-II increased gradually. Once T decreased to 174 °C and lower, the NE of iPP/WBG-II became higher than that of iPP/CNTs; meanwhile, WBG-II began to play determining role in the polymorphic composition and enhanced the β-phase proportion of iPP nucleated with CNTs/WBG-II. The findings of this study brought a new pathway to control the polymorphic composition and mechanical properties of iPP/CNTs composites. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, the melt structure of isotactic polypropylene (iPP) nucleated with α/β compounded nucleating agents (α/β-CNA, composed of the α-NA of 0.15 wt % Millad 3988 and the β-NA of 0.05 wt % WBG-II) was tuned by changing the fusion temperature Tf. In this way, the role of melt structure on the crystallization behavior and polymorphic composition of iPP were investigated by differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXD) and scanning electron microscopy (SEM). The results showed that when Tf = 200°C (iPP was fully molten), the α/β-CNA cannot encourage β-phase crystallization since the nucleation efficiency (NE) of the α-NA 3988 was obviously higher than that of the β-NA WBG-II. Surprisingly, when Tf was in 179-167°C, an amount of ordered structures survived in the melt, resulting in significant increase of the proportion of β-phase (achieving 74.9% at maximum), indicating that the ordered structures of iPP played determining role in β-phase crystallization of iPP nucleated with the α/β-CNA. Further investigation on iPP respectively nucleated with individual 3988 and WBG-II showed that as Tf decreased from 200°C to 167°C, the crystallization peak temperature Tc of iPP/3988 stayed almost constant, while Tc of iPP/WBG-II increased gradually when Tf < 189°C and became higher than that of iPP/3988 when Tf decreased to 179°C and lower, which can be used to explain the influence of ordered structure and α/β-CNA on iPP crystallization. Using this method, the selection of α-NA for α/β-CNA can be greatly expanded even if the inherent NE of β-NA is lower than that of the α-NA. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41355. [ABSTRACT FROM AUTHOR]

In this study, the effects of crystallization conditions (cooling rate and end temperature of cooling) on crystallization behavior and polymorphic composition of isotactic polypropylene/multi-walled carbon nanotubes (iPP/MWCNTs) composites nucleated with different concentrations of β-nucleating agent (tradename TMB-5) were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and scanning electronic microscopy (SEM). The results of DSC, WAXD and SEM revealed that the addition of MWCNTs and TMB-5 evidently elevates crystallization temperatures and significantly decreases the crystal sizes of iPP. Because of the competition between α-nucleation (provided by MWCNTs) and β-nucleation (induced by TMB-5), the β-phase crystallization takes place only when 0.15 wt% and higher concentration of TMB-5 is added. Non-isothermal crystallization kinetics study showed that the crystallization activation energy Δ E of β-nucleated iPP/MWCNTs composites is obviously higher than that of pure iPP, which slightly increases with the increase of TMB-5 concentration, accompanying with the transition of its polymorphic crystallization behavior. The results of non-isothermal crystallization and melting behavior suggested that the cooling rate and end temperature of cooling ( Tend) are important factors in determining the proportion and thermal stability of β-phase: Lower cooling rate favors the formation of less amount of β-phase with higher thermal stability, while higher cooling rate encourages the formation of higher proportion of β-phase with lower thermal stability. The Tend = 100°C can eliminate the β-α recrystallization during the subsequent heating and therefore enhance the thermal stability of the β-phase. By properly selecting TMB-5 concentration, cooling rate and Tend, high β-phase proportion of 88.9% of the sample was obtained. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A previous work reported that the polymorphic crystallization behavior of isotactic polypropylene (iPP) can be efficiently tuned by the combination of controlling the melt structure (i.e., creation of an ordered structure by tuning the fusion temperature T by self-nucleation) and the addition of the α-/β-dual-selective nucleation agent (dual-selective β-NA, tradename WBG-II). In this study, we further investigated the impact of isothermal treatment on the polymorphic behavior and the isothermal crystallization kinetics of a β-iPP sample with different melt structures by differential scanning calorimetry (DSC). The results of isothermal crystallization kinetics study illustrated that as T decreased gradually from Region I to Region II and Region III, two sharp increases of the crystallization rate took place at the transition temperatures of Region II, showing that the enhancement of β-phase crystallization took place in a certain crystallization rate window. The calculation of the Avrami exponent n revealed that the two-dimensional growth of crystallites with instantaneous nucleation took place before and after the occurrence of the synergetic effect between the ordered structures and the dual-selective β-NA (when Tf ≥ 168 °C). Moreover, it was found that the occurrence of the synergetic effect in the fusion temperature range of Region II can evidently enhance the β of the sample: by tuning the fusion temperature T and the isothermal crystallization temperature T, the relative percentage of β-phase (β) of the single β-iPP sample with only 0.03 wt.% β-NA can be efficiently tuned in the wide β range of 0 %-95.0 %; meanwhile, the sensitivity of β to the isothermal crystallization temperature T was reduced. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, the crystallization behavior of the β-isotactic polypropylene (β-iPP) samples nucleated by a rare earth based β-nucleating agent (β-NA) WBG-II and a metal salts compound β-NA NAB83 (denoted as WPP and NPP, respectively) under different cooling conditions were comparatively investigated. The thermal conditions such as the cooling rate, isothermal crystallization temperature, isothermal crystallization time, and the subsequent cooling to room temperature. The results of WAXD, SEM, and nonisothermal crystallization reveal that under the same processing conditions, the crystallite size of NPP is smaller, which arrange more compactly as compared with WPP. Meanwhile, NPP has shorter crystallization rate and higher β-nucleation selectivity, but WPP can crystallization at wider temperature range. The results of isothermal crystallization showed that NPP has higher selectivity and higher β-nucleation efficiency, which favors the formation of high proportion of β-phase at the isothermal crystallization temperature of 110-130°C with and without subsequent cooling; WPP has lower selectivity, which can only induce high content of β-phase under isothermal crystallization without subsequent cooling to 25°C. In tuning the crystallization behavior and the properties of β-PP, the joint influence of the efficiency and selectivity of the β-NA, and the thermal conditions should be taken into consideration. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40115. [ABSTRACT FROM AUTHOR]

In the previous work, we reported that the β-selectivity, morphology and tensile behavior of isotactic polypropylene (iPP) can be efficiently tuned by the combination of controlling the melt structure status (namely, creation ordered structure by tuning the fusion temperature T) and the addition of β-nucleation agent (β-NA, tradename WBG-II, concentration 0.01 wt%), which was called 'Ordered Structure Effect' (OSE). This study further investigates the dynamic crystallization and melting behavior of β-iPP with a different melt structure status by differential scanning calorimentry (DSC) and non-isothermal crystallization kinetics. The results revealed that under all the cooling rates studied (2, 5, 10, 20 and 40 °C/min), the crystallization temperature on the cooling curves increased gradually with the decrease of T; meanwhile, when the T was in the temperature range of 168-186 °C where the OSE occurs (defined as Region II), the crystallization activation energy ΔE was found to be evidently lower, compared with that when the T was higher than 186 °C or lower than 168 °C. The results of the subsequent heating showed that the occurrence of the OSE can be observed at all the cooling rates studied; the location of the Region II was constant when the cooling rate varied. Low cooling rate encouraged the formation of more β-phase triggered by OSE. Moreover, the role of OSE on the β-α recrystallization was comparatively studied by tuning the end temperature of recooling (T) after held at T, and it was found that the OSE encouraged the formation of β-phase with high thermal stability at the low temperature part of Region II, while enhancing the β-crystal with relatively low thermal stability at the high temperature part of Region II. [ABSTRACT FROM AUTHOR]

The selectivities of different β-nucleating agents might be quite different from each other, which is important in determining the crystallization and properties of the obtained β-isotactic polypropylene ( β-iPP). However, the relationship between molecular structure and dynamic crystallization behavior of β-iPP nucleated by dual-selective β-nucleating agent (DS- β-NA) is still not clear. In this study, the dynamic crystallization and melting behavior of two β-iPP with nearly same average isotacticity but different stereo-defect distribution, nucleated by a DS- β-NA ( N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide; trade name TMB-5), were studied by differential scanning calorimetry, wide-angle X-ray diffraction, and scanning electronic microscopy. The results indicated that in the presence of TMB-5, the dynamic crystallization and melting behavior of the samples are quite different because the joint effects of the dual selectivity of TMB-5 and stereo-defect distribution of the iPP under different cooling rates. Two important roles were observed: (i) slow cooling rate favors the formation of high β-fraction; and (ii) high crystallization temperature favors the crystallization of α-phase accelerated by TMB-5. Generally, the dual selectivity of the DS- β-NA, the stereo-defect distribution of iPP, and the cooling rate were important factors in determining the formation of β-crystal. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The influence of the hydrogenated petroleum resin P125 on the crystallization behavior, crystallization kinetics, and optical properties of polypropylene (PP) were investigated. The results of differential scanning calorimetry, successive self-nucleation, and annealing fractionation demonstrated that P125 reduced the interaction between the PP molecules, decreased the crystallization, prevented PP from forming thick lamellae, and encouraged the formation of thin lamellae. The isothermal crystallization kinetics, self-nucleation isothermal crystallization kinetics, and polarized optical microscopy observations showed that P125 slightly decreased the nucleation rate, significantly decreased the crystal growth rate, generally reduced the overall crystallization rate, and effectively deceased the crystallite sizes of PP. The optical properties studies showed that P125 effectively decreased the haze and increased the surface glossiness and yellowness index of PP. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

In this work, both hexene copolymerized polyethylene of TR-571 and homopolymerized polyethylene of 5000s were ram extruded using a temperature window effect. The rheological results show that the extrusion pressures abruptly drops at very narrow extrusion temperature windows for the two types of polyethylenes, but the window range (150-155°C) of TR-571 are higher about 6°C than that of 5000s, and the threshold melt velocity value (where the window effect set in) for TR-571 is remarkably lower than that of 5000s. Besides, the differential scanning calorimeter experiments indicate that the melting points ( T m) of the extrudates obtained inside the temperature window are lower 3.74-4.56°C than those obtained outside, whereas the crystallization peak temperatures ( T c) of the former are higher 3.29-3.57°C than those of the later. The crystal orientation, shown in the photographs of wide-angle x-ray diffraction and scanning electron microscope, indicates that the chain alignment induced by elongational flow in the temperature window can at least be partially maintained and leave a structure memory in the melt state. Successive self-nucleation and annealing fractionation results suggest that these well-aligned chains as the result of structure memory effect can act as a nucleating agent in the crystallization process. Thus, the number of the lamellae increases and the thickness decrease, which finally leading to higher T c and lower T m of extrudates obtained inside a temperature window. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

Large amount of work has be published on the dynamic crystallization and melting behavior of β-nucleated polypropylene (β-PP). However, the relationship between molecular structure and dynamic crystallization behavior of β-PP is still not clear. In this study, the dynamic crystallization and melting behavior of two β-nucleated isotactic polypropylene (β-iPP) with nearly same average isotacticity but different stereo-defect distribution, were studied by differential scanning calorimetry (DSC), wide angel X-ray diffraction (WAXD) and temperature modulated DSC (TMDSC). The results indicated that stereo-defect distribution of iPP can significantly influence the dependence of the β-crystal content and thermal stability on the cooling rate. NPP-A with less uniform stereo-defect distribution favors the crystallization at higher temperature region and the formation of β-crystal with high thermal stability in all cooling rates concerned, moreover, the β-crystal content is influenced by cooling rate; for NPP-B with more uniform distribution of stereo-defect, the crystallization temperature and the regular insertion of molecular chains can be reduced in a larger extent. NPP-B is more suitable for the formation of high proportion of β-crystal in both low and high cooling rates, meanwhile, the thermal stability of crystal is sensitive to the cooling rate. This work provides a new insight into the design of β-iPP in dynamic crystallization. [ABSTRACT FROM AUTHOR]

Two isotactic polypropylene (iPP) samples (PP-A and PP-B) were obtained by utilizing two different heterogeneous Ziegler-Natta catalysts in a given polymerization system. The molecular structure and conformational behavior of the samples were studied. The results of determination of xylene soluble material (XS) and 13C NMR showed that the average isotacticity of the samples were nearly same. However, the results of high-resolution high-temperature 13C NMR (HRHT 13C NMR) and successive self-nucleation and annealing (SSA) fractionation revealed that the amount of high isotacticity of PP-B was lower than that of PP-A, and the amount of relative medium and low isotacticity of PP-B was higher than PP-A, indicating that the stereodefect distribution of PP-B was more uniform than PP-A. The calculation of average meso sequence length from SSA was found to be in good agreement with that calculated from the results of HRHT 13C NMR. Moreover, Fourier transformation infrared was utilized to study the influence of stereodefect distribution on the conformational behavior of iPP. The result suggested that the molecular conformation of the PP-B was more disordered than PP-A, the regularity of molecular structure for PP-B was lower than that of PP-A. The related action mechanism and the influences of which on crystallization behavior were discussed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

In the present study, we investigated the influences of polymerization and crosslinking technologies on the branched-chain structures, crystallization behaviors, and gel networks of two types of low-density polyethylenes, LDPE1 and LDPE2, polymerized under different polymerization conditions in commercial large-capacity production lines. High temperature 13C NMR analysis suggests that the molar contents of both long-chain branches and short-chain branches of LDPE2 were markedly higher than those of LDPE1 due to a higher polymerization temperature for LDPE2. The high content of chain branches of LDPE2 leads to its relatively higher storage modulus, entanglement density, and gel content, as indicated by dynamic mechanical analysis. In addition, when the crosslinking temperature reached 180°C, the LDPE2 crosslinked with 2 wt% dicumylperoxide (XLPE2-D2) displayed a relatively wider processing time window and a faster crosslinking rate than XLPE1-D2. Successive self-nucleation and annealing fractionation indicated that increasing the concentration of dicumylperoxide can improve the crosslinking degree, but resulted in lower crystallinity and thinner lamellar crystals. [ABSTRACT FROM PUBLISHER]

The effects of ethylene units content and crystallization temperature on the conformations, and the thermal and crystallization behavior were investigated by a combination of Fourier transform infrared (FTIR) spectroscopy, wide angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). The characterization of FTIR spectroscopy proves that the longer helical conformation sequences of the propylene–ethylene random (PER) samples decrease, whereas the shorter helical conformation sequences increase with the increase in ethylene units content. The increase of the shorter helical conformation sequences is favorable for the formation of the γ-phase in the crystals. A group of broad endothermic peaks can be seen clearly in the DSC curves of PER copolymers, which may be associated with the melting of mixtures of the α- and γ-forms in the crystals. The melting point, crystallization temperature, and crystallinity degree of the PER copolymers decrease with the increase in ethylene units contents. Three typical melting peaks of the PER copolymers crystallized isothermally between 80°C and 130°C were observed. The two higher melting peaks result from melting of the α- and γ-phase in the crystals, whereas the materials crystallized on quenching give the lowest peak. The WAXD results confirm that the PER copolymers crystallize from the melt, as mixtures of α and γ forms, in a wide temperature range. The critical number ζlim of the crystallizable units for the α-form increases with the increase in crystallization temperature for PER copolymers, which is favorable for the formation of the γ phases. The amount of γ-form increases with the increase in crystallization temperature at the expense of its α component, then reaches a maximum value at the crystallization temperature of 115°C, and finally decreases with further increase in the crystallization temperature. [ABSTRACT FROM AUTHOR]

In this study, one of the commonly used MXene (Ti3C2Tx) and β nucleated isotactic polypropylene (β-iPP)/MXene composites of different compositions were fabricated. The effects of MXene on non-isothermal crystallization and polymorphic behavior of β-iPP/MXene composites were comparatively studied. The non-isothermal crystallization kinetics indicates that for all samples, the lower cooling rates promote composites to crystallize at higher temperatures. When MXene and β-Nucleating agent (β-NA) are added separately, the crystallization temperature of composites shifts towards higher temperatures at all cooling rates. When MXene and β-NA are added simultaneously, the composite shows different cooling rate dependence, and the effects of improving crystallization temperatures is more obvious under rapid cooling. The activation energy of four samples iPP, iPP/MXene, iPP/β-NA, and iPP/MXene/β-NA were −167.5, −185.5, −233.8, and −218.1 kJ/mol respectively, which agree with the variation tendency of crystallization temperatures. The polymorphic behavior analysis obtained from Differential Scanning calorimetry (DSC) is affected by two factors: the ability to form β-crystals and the thermal stability of β-crystals. Because β-crystals tend to recrystallize to α-crystals below a critical temperature, to eliminate the effect of β-α recrystallization, the melting curves at end temperatures Tend = 50 °C and Tend = 100 °C are comparatively studied. The results show that more thermally unstable β-crystals would participate in β-α recrystallization with higher cooling rates. Moreover, thermal stability of β-crystals is improved by adding MXene. To further verify these findings, samples of three different thermal conditions were synthesized and analyzed by DSC, X-Ray Diffraction (XRD), and Polarized Light Optical Microscopy (PLOM), and the results were consistent with the above findings. New understandings of synthesizing β-iPP/MXene composites with adjustable morphologies and polymorphic behavior were proposed. [ABSTRACT FROM AUTHOR]

The effects of MXene on the crystallization behavior of β-nucleated isotactic polypropylene (iPP) were comparatively studied. The commonly used MXene Ti3C2Tx was prepared by selective etching and its structure and morphology were studied in detail. Then MXene and a rare earth β-nucleating agent (NA) WBG-II were nucleated with iPP to prepare samples with different polymorphic compositions. The crystallization, melting behavior, and morphologies of neat iPP, iPP/MXene, iPP/WBG-II, and iPP/MXene/WBG-II were comparatively studied. The crystallization behavior analysis reveals that a competitive relationship exists between MXene and WBG-II when they were compounded as α and β nucleating agents. In the system, the β-nucleation efficiency (NE) of WBG-II is higher than α-NE of MXene. The β-phase has relatively low thermal stability and would transform to α-phase when cooled below a critical temperature. [ABSTRACT FROM AUTHOR]

In this article, hyperbranched polyester grafted graphene oxide (GO) was successfully prepared. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) were performed for its characterizations. On the other hand, differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) were also performed to study its influences on non-isothermal crystallization behaviors of β-nucleated isotactic polypropylene (β-iPP). The grafting ratios of hyperbranched polyester with different supermolecular structures were calculated to be 19.8–24.0 wt %, which increase with the degree of branching. The results showed that the grafting of hyperbranched polyester was advantageous in increasing the crystallization peak temperature Tp and decreasing the crystallization activation energy ΔE of β-iPP/GO composites, which contributed to the iPP's crystallization process. Moreover, under all cooling rates (2, 5, 10, 20, 40 °C/min), crystallinities of β-iPP/GO were greatly improved after being grafted with hyperbranched polyester, because of the increase of the relative contents of α-phase αc and the average α-crystal sizes. [ABSTRACT FROM AUTHOR]

Polyphenylene sulfide (PPS) has a prospective application in high-frequency communication due to its excellent dielectric properties. However, owing to the strong melt memory effect, the crystalline structure of PPS is very sensitive to the processing conditions and difficult to be controlled. To date, the melt memory effect of polymer cannot be detected directly and quantitatively. In this work, four PPS samples were successively prepared via polymerization, extrusion and dissolution treatment. The Fourier infrared transform spectroscopy (FTIR), high-temperature gel permeation chromatography (HT-GPC) and dynamic rheological tests disclose that these four PPS samples have analogous molecular structure and only differ in entanglement density. The molecular weight between entanglements (M e) decreases gradually from 1188 to 354 g/mol. Furthermore, differential scanning calorimetry (DSC) and polarized optical microscopy (POM) measurements were carried out to study the effect of entanglement density on the crystallization kinetics of PPS. It is found that entanglement density is a key indicator to characterize the melt memory effect of PPS semi-quantitatively, and the residual local ordered structures in PPS melt is proportional to M e. In addition, the crystallization kinetics of PPS is determined by the cooperation of melt memory effect (nucleation) and entanglement density (growth). Accordingly, the relationship of "chain entanglements" → "melt memory effect" → "crystallization behavior" of PPS is established, constructing a roadmap for the precise control of crystalline structures of PPS products during practical processing. Diagram of the relationship of "chain entanglements" → "melt memory effect" → "crystallization behavior" of PPS. [Display omitted] • Entanglement density of PPS was controlled by different methods (1188-354 g/mol). • Entanglement density can be used to characterize the memory effect of PPS. • Memory effect and entanglement together affect the crystallization kinetics of PPS. [ABSTRACT FROM AUTHOR]

Abstract: The effects of ultrasonic irradiation on conformation and crystalline structure of isotactic polypropylene (iPP) and β-isotactic polypropylene (β-iPP) were studied by means of Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The results demonstrate that ultrasonic irradiation decreases the helical conformation order and changes the crystalline structures: for iPP, T m and T onset decrease, T m − T onset becomes larger; for β-iPP, the β c, (1 − λ)β and k β increase, the intensities of α(040) plane and α(130) plane in WAXD profiles decrease evidently. For both iPP and β-iPP, the crystallinity decreases, d-spacing increases, the crystallite size L decreases and ultrasound shows a selective effect on the growth of β-crystal. Furthermore, DSC and WAXD were employed to observe the effect of ultrasound on the “melting memory effect” of β-iPP. The results indicate that ultrasonic irradiation destructs the existing “locally ordered structure” in β-iPP melt, as a result greatly inhibits the βα-recrystallization of β-iPP samples during heating. [Copyright &y& Elsevier]

Polyphenylene sulfide (PPS) is one of most widely used special engineering plastics in the world. However, owing to the unique memory effect and thermal degradation effect, the crystalline structure of PPS is extremely difficult to control during the practical processing, resulting in the deterioration of processability and performance of PPS products. In this work, the differential scanning calorimetry (DSC), polarized optical microscopy (POM), in-situ X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR) and rheological tests were carried out to distinguish these two effects on the crystallization behavior of PPS systematically. It is found that the memory effect and thermal degradation compete "as one falls, another rises" on the crystallization behavior of PPS, both of which accelerate the crystallization rate and reduce the uniformity of crystalline structure. The residual of local ordered structures in PPS melt increases the nucleation rate significantly and could be eliminated as the pre-treatment temperature (T p) reaches 350 °C. Nevertheless, the chain scission reaction is activated and dominates the crystallization process of PPS when T p is higher than 350 °C, leading to the notable promotion of crystal growth rate. Accordingly, processing around the transition temperature can minimize the cooperation of melt memory and thermal degradation on the crystallization behavior of PPS, resulting in the lowest crystallization rate and the most uniform crystal size distribution. Diagram of competition of memory effect and thermal degradation on the crystallization behavior of PPS. [Display omitted] • Memory effect and thermal degradation occur inevitably of PPS. • PPS has a unique crystallization behavior due to memory effect and chain scission. • Both effects can be minimized at the pre-treatment temperature of 340–350 °C. [ABSTRACT FROM AUTHOR]

Polypropylene random copolymer (PPR) is one of important polypropylene types for the application fields. However, due to the random copolymer chain configuration, it is difficult to obtain high proportion of β-phase even under the influence of β-nucleating agent (β-NA). In this study, the melt structure (namely, the content of ordered structures in the melt) of β-nucleated ethylene-copolymerized PPR (β-PPR) was controlled by tuning the fusion temperature ( T f ), and its impact on the crystallization and polymorphic behavior of β-PPR was investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), polarized optical microscopy (PLM) and scanning electronic microscopy (SEM). The result revealed that compared with the β-nucleated iPP homo-polymer, it is more difficult for β-PPR to form β-crystals; interestingly, when T f is in the temperature range of 162–173 °C, the ordered structures survived in melt exhibit high β-nucleation efficiency under the influence of β-NA, resulting in significant increase of β-phase proportion and evident variation of crystalline morphology, which is called the Ordered Structure Effect (OSE). Moreover, through investigating the self-nucleation behavior and equilibrium melting temperature of pure PPR (non-nucleated PPR), the physical nature of the lower and upper limiting T f temperatures for the occurrence of OSE in β-PPR was explored; the role of ethylene co-monomer in the occurrence of OSE was discussed. [ABSTRACT FROM AUTHOR]

To elucidate influence of molecular weight on crystallization behavior of β-nucleated isotactic polypropylene (β-nucleated iPP) with different melt structures, a series of β-nucleated iPP with varying molecular weights were prepared. Results revealed that higher iPP molecular weight was more favorable for formation of high β-phase proportion ( β c ). By tuning heating temperature ( T f ), the melt structure (content of ordered structures within melt) of β-nucleated iPP was controlled. It was found that for all samples, β c evidently elevated with decrease of T f , indicating occurrence of synergetic effect between ordered structures and β-NA (ordered structure effect, OSE); with decrease of iPP molecular weight, β c triggered by OSE increased gradually and T f temperature range for occurrence of OSE gradually decreased. Moreover, as holding time at T f increased from 1 to 120 min, subsequent melting curves of samples stayed unchanged, reflecting very high thermal stability of the ordered structures, being independent to iPP molecular weight. [ABSTRACT FROM AUTHOR]

Highlights: [•] HDPE/EVA blends undergo phase separation, making it an interesting topic to investigate the relationships between miscibility and crystallization. [•] Influences from blending on the crystallization kinetics were successfully evaluated by Friedman's and Khanna's method. [•] X-ray diffraction studies revealed that blending with EVA the unit length of the unit cell of the HDPE increases. [•] Thermal fractionation method was successfully used to characterize the co-crystallization in HDPE/EVA blends. [ABSTRACT FROM AUTHOR]

Abstract: In this work, montmorillonite (Mt) was modified by octadecyl amine ethoxylate ether (A) which has two poly(ethylene oxide) segments. Montmorillonite/polypropylene (Mt/PP) nanocomposites were prepared by a melt blending technique using different contents of modified Mt with and without maleic anhydride grafted polypropylene (PPg). The intercalated and exfoliated structures of Mt/PP nanocomposites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Because of the typical intercalated and exfoliated structures, the mechanical properties of Mt/PP nanocomposites were improved significantly. The modified Mt in a PP matrix led to a significant reduction of melt viscosity and enhancement in Izod-notched impact strength and elongation at break. The Izod-notched impact strength and elongation at break of Mt/PP nanocomposites were 1.95 and 2.77 times as high as those of pure PP. The tensile strength of Mt/PP nanocomposites was also improved in the presence of PPg. [Copyright &y& Elsevier]