Preparation and crystallization behaviour of PP/PP-g-MAH/Org-MMT nanocomposite

The melt-direct intercalation method was employed to prepare polypropylene (PP)/maleic anhydride grafted polypropylene (PP-g-MAH)/organic-montmorillonite (Org-MMT), X-ray diffractometer was used to investigate the intercalation effect and crystallite size in composites and TEM micrograph to observe the dispersion of Org-MMT interlayers in polypropylene. The results showed that by introducing maleated polypropylene in PP/Org-MMT composite, macromolecule segments had intercalated into interlayer space of Org-MMT. As a result, Org-MMT interlayers were dispersed evenly in polypropylene and PP/PP-g-MAH/Org-MMT nanocomposite was synthesized. The crystallite size of nanocomposite perpendicular to the crystalline plane such as (0 4 0), (1 3 0), (1 1 1), (0 4 1) is smaller than that of pristine PP, which indicated that the crystallite size of PP in nanocomposite can be diminished by adding PP-g-MAH and Org-MMT in PP. Moreover, the nonisothermal crystallization kinetics of PP and PP/PP-g-MAH/Org-MMT nanocomposite was investigated by differential scanning calorimetry (DSC) with various cooling rates. The Avrami analysis modified by Jeziorny, Ozawa method and a method developed by Liu were employed to describe the nonisothermal crystallization process of these samples. The difference in the exponent n between PP and nanocomposite, indicated that nonisothermal kinetic crystallization corresponded to tridimensional growth with heterogeneous nucleation. The values of half-time, Z_c, F(T) and K(T) showed that the crystallization rate of composites was faster than that of PP at a given cooling rate.     

Non-isothermal crystallization kinetics of UHMWPE composites filled by oligomer-modified CaCO3

The processability of ultrahigh molecular weight polyethylene (UHMWPE) improved by oligomer-modified calcium carbonate (CaCO₃) was observed in our previous work. In order to understand the effect of oligomer-modified CaCO₃ on the crystallization of UHMWPE, the non-isothermal crystallization behavior and crystallization kinetics of UHMWPE composites filled by oligomer-modified CaCO₃ was studied by differential scanning calorimetry in this work. Jeziorny and Mo methods were used to describe the non-isothermal crystallization kinetics of UHMWPE composites. The effect of modified filler content and cooling rate on the crystallization temperature and crystallization rate was discussed. The heterogeneous nucleation of modified CaCO₃ slightly increases the crystallization temperature of UHMWPE. The crystallization enthalpy of UHMWPE composites is significantly higher than that of UHMWPE. The crystallization rate of UHMWPE composites depends on the filler contents and cooling rate.

     

Non-Isothermal Crystallization of Poly(vinylidene Fluoride)/Multiwalled Carbon Nanotube Composites

Poly(vinylidene fluoride)/multiwalled carbon nanotube (PVDF/MWCNT) composites were prepared by the method of solution blending. The non-isothermal crystallization of PVDF and its composites was investigated by differential scanning calorimetry (DSC). The results showed that the crystallization peaks shifted to lower temperature and the exothermic trace became wider when cooling rate increased for PVDF and its composites. The MWCNTs caused an increase in crystallization temperature and initial crystallization temperature. In addition, the Jeziorny and Mo methods were used to analyze the non-isothermal crystallization kinetics. The results showed that the crystallization rate rose with an increase in cooling rate, however, the MWCNTs decreased the crystallization rates of PVDF.     

Non-isothermal crystallization of polyethylene blends with bimodal molecular weight distribution

Non-isothermal crystallization of polyethylene (PE) blends with bimodal molecular weight distribution (MWD) was investigated by differential scanning calorimetry (DSC) at various scanning rates. The bimodal PE blends were prepared by blending two unimodal polyethylenes with large difference in molecular weigh in different ratio in xylene solution. Different kinetic parameters such as the half-time of crystallization (t_1/2), crystallization rate constant (Z_c), F(T) and the effective activation energy were determined. Some complicated relationships between these parameters and the average molecular weight were found. The crystallization rate first increased and reached a maximum then decreased, and also correlated with the MWD. The Avrami index under non-isothermal conditions was analyzed with a method developed by Harnisch and Muschik; the results indicated that homogeneous nucleation and spherulitic growth regimes were present in all samples studied.     

Non-isothermal crystallization kinetics of continuous glass fiber-reinforced poly(ether ether ketone) composites

Current studies on crystallization kinetics for glass fiber-reinforced poly(ether ether ketone) mainly focused on short glass fiber-reinforced composites and their isothermal crystallization. It is worth noting that continuous glass fiber-reinforced poly(ether ether ketone) composite (CGF/PEEK) possesses relatively higher mechanical performance than short fiber-reinforced PEEK under high temperature. Here, for the first time, we investigate the non-isothermal crystallization kinetics and melting behavior of CGF/PEEK by differential scanning calorimetry at four different cooling rates. By evaluating the crystallite size of CGF/PEEK using X-ray diffraction, it is found that with the decreasing cooling rate, the crystallite size distribution evolves more uniform, and the size of crystallites enlarges. Besides, by systematical analysis, we find the modified Avrami equation can well describe crystallization behavior of the CGF/PEEK. The higher Avrami value of CGF/PEEK than pure PEEK indicates that CGF could introduce a more complex geometry effect on the crystallization. The addition of CGF greatly reduces the absolute value of crystallization activation energy of PEEK, suggesting that CGF can reduce the nucleation energy barrier. The obtained results illustrate that CGF can accelerate the nucleation rate due to heterogeneous nucleation while reduce the growth rate due to retarded polymer chain mobility. And the cooling conditions can influence crystal growth and morphology.

     

Influence of <Emphasis Type="Italic">m</Emphasis>-isopropenyl-α,α-dimethylbenzyl isocyanate and styrene on non-isothermal crystallization behavior of polypropylene

Non-isothermal crystallization kinetics of polypropylene (PP), m-isopropenyl-α,α-dimethyl-benzyl isocyanate grafted PP (PP-g-m-TMI), and styrene(St), as comonomer, together with m-TMI grafted PP (PP-g-(St-m-TMI)) was investigated by using differential scanning calorimetry (DSC) under different cooling rates. The crystallization rates of all samples increased with increasing cooling rate. The relation of the half time of crystallization (t _1/2) of the three samples, t _{1/2(PP-g-(St-m-TMI))} < t _{1/2(PP-g-m-TMI)} < t _1/2(PP), implying the introduction of St could effectively improve the degree of grafting of m-TMI, resulting in crystallization temperature increased, and the crystallization rate was the fastest. Three methods, namely, the Avrami, the Ozawa, and the Mo, were used to describe the crystallization process of the three samples under non-isothermal conditions. The Avrami and Ozawa neglected the secondary crystallization that follows primary crystallization. The Mo method can successfully describe the overall non-isothermal crystallization process of all the samples. It has been found that the F(T)_{(PP-g-(St-m-TMI))} < F(T)_(PP-g-m-TMI) < F(T)_(PP), also meaning that the crystallization rate of PP-g-(St-m-TMI) and PP-g-m-TMI were faster than that of PP. The activation energy (ΔE) for non-isothermal crystallization of all samples was determined by using the Kissinger method. The result showed that the lower value of ΔE for crystallization obtained for PP-g-m -TMI and PP-g-(St-m-TMI) confirmed the nucleating effect of St and m-TMI on crystallization of PP.     

聚-4-乙基苯酚抗氧剂对聚丙烯结晶行为的影响

通过差示扫描量热仪(DSC)和X射线粉末衍射仪(XRD)研究了聚-4-乙基苯酚抗氧剂对聚丙烯结晶行为的影响。 分别用Jeziorny法和Mo法处理非等温结晶动力学。 同时用Friedman法和Kissinger法计算其结晶活化能。 最后由结晶活化能与结晶温度的变化曲线求得Hoffman-Lauritzen参数成核速率常数(K_g)和迁移活化能(U^*)值,进而求得折叠链端表面自由能(σ_e)和分子链段折叠功(q)。 结果表明,抗氧剂的加入,使聚丙烯的结晶峰温度向低温区移动,结晶半峰宽变大,半结晶时间(t_1/2)增大,Jeziorny法所得的结晶速率常数(Z)降低,Mo法所得反映结晶速率快慢的参数F(T)提高,在相同结晶转化率下,结晶活化能负值变小。 Hoffman-Lauritzen参数K_g、U^*、σ_e和q值均增大。 所有变化均表明聚-4-乙基苯酚抗氧剂对PP的结晶有抑制作用。     

Nonisothermal crystallization kinetics of in situ nylon 6/graphene composites by differential scanning calorimetry

The nonisothermal crystallization kinetics was investigated by differential scanning calorimetry for the nylon 6/graphene composites prepared by in situ polymerization. The Avrami theory modified by Jeziorny, Ozawa equation, and Mo equation was used to describe the nonisothermal crystallization kinetics. The analysis based on the Avrami theory modified by Jeziorny shows that, at lower cooling rates (at 5, 10, and 20 K/min), the nylon 6/graphene composites have lower crystallization rate than pure nylon 6. However, at higher cooling rates (at 40 K/min), the nylon 6/graphene composites have higher crystallization rate than pure nylon 6. The values of Avrami exponent m and the cooling crystallization function F(T) from Ozawa plots indicate that the mode of the nucleation and growth at initial stage of the nonisothermal crystallization may be as follows: two‐dimensional (2D), then one‐dimensional (1D) for all samples at 5–10 °C/min; three‐dimensional (3D) or complicated than 3D, then 2D and 1D at 10–20 and 20–40 °C/min. The good linearity of the Mo plots indicated that the combined approach could successfully describe the crystallization processes of the nylon 6 and nylon 6/graphene composites. The activation energies (ΔE) of the nylon 6/graphene composites, determined by Kissinger method, were lower than those of pure nylon 6. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1381–1388, 2011     

Effect of functionalization on non-isothermal crystallization behavior of polypropylene

The non-isothermal crystallization kinetics of three functionalized polypropylenes (PPs; polypropylenes-g-acrylic acid [PP-g-AA], polypropylenes-g-glycidyl methacrylate [PP-g-GMA], polypropylenes-g-maleic anhydride [PP-g-MAH]) at different cooling rates were investigated by differential scanning calorimetry, using the Jeziorny method, Ozawa method, and Mo method. The result showed that Mo method can adequately describe the non-isothermal crystallization kinetics of pure PP and functionalized PPs, and at a given relative crystallinity, the crystallization rate obtained using Mo method followed an order of PP-g-AA > PP-g-GMA > PP > PP-g-MAH. The crystallization activation energy for these samples was calculated using Kissinger's method, which indicated that the introduction of monomers had a confinement effect on the motion of PP chains.     

Nucleation Activation and Spherical Crystals Morphology of LLDPE/LDPE/TiO2 Nanocomposites Prepared by Non-Isothermal Crystallization

The nucleation activation of TiO₂ nanoparticles in the linear low-density polyethylene (LLDPE)/low-density polyethylene (LDPE)/TiO₂ nanocomposites prepared by non-isothermal crystallization, the spherical crystals morphology of the etched LLDPE/LDPE and LLDPE/LDPE/TiO₂ composites were investigated by differential scanning calorimetry (DSC) and field-emission scanning electron microscopy (FE-SEM), respectively. The results showed that the heterogeneous nucleation activation of TiO₂ nanoparticles was accelerated by the fast cooling rate. The spherical crystals in the LLDPE/LDPE and LLDPE/LDPE/TiO₂ composites were ascribed to the same crystal structure. It was worth to note that there was distinct difference between the morphology of the cocrystallization LLDPE/LDPE crystals and that of the independent crystallization LLDPE/LDPE crystals.     

Effect of silver nanoparticles on the morphology,crystallization, and melting behavior of polypropylene: A study on non-isothermal crystallization kinetics

The nanocomposites were prepared using melt intercalation method and the effects of the processing conditions on silver nanoparticles dispersion were investigated by transmission electron microscopy. Non-isothermal crystallization kinetics of virgin polypropylene (PP) and its nanocomposites have been evaluated using differential scanning calorimetric technique. The non-isothermal crystallization melt data were analyzed using macro kinetics equation with the help of Avrami, Malkin, and Mo’s models. The crystallization rate increased with the increasing of cooling rates for virgin PP and nanocomposite, but the crystallization of nanocomposite was faster than that of PP at a given cooling rate. The activation energy for non-isothermal crystallization of virgin polymer and nanocomposites based on Kissinger method has been determined to be 186 and 211 kJ/mol, respectively. Transmission electron microscopy analysis reveals balanced dispersion and presence of some silver nanoparticles aggregates, which act as a heterogeneous nucleating agent during the crystallization of the nanocomposite.     

Non-isothermal crystallization kinetics and morphology of wollastonite-filled β-isotactic polypropylene composites

To obtain wollastonite-filled β-iPP composites, the wollastonite with β-nucleating surface (β-wollastonite) was prepared through chemical reaction between wollastonite with α-nucleating surface (α-wollastonite) and pimelic acid. The formation of calcium pimelate on the surface of wollastonite was proved using Fourier transform infrared spectrometry and scanning electron microscopy. The crystallization behavior, melting characteristics, non-isothermal crystallization kinetics, and crystalline morphologies of α- and β-wollastonite-filled iPP composites were studied by differential scanning calorimetry and polarizing optical microscopy. It is found that the crystallization peak temperatures of β-wollastonite-filled iPP composites were higher than that of α-wollastonite-filled iPP composites, which indicated that wollastonite with β-nucleating surface has stronger heterogeneous nucleation than that of wollastonite with α-nucleating surface. Although the crystallization temperatures of iPP and iPP composites decreased with increasing cooling rates, α-wollastonite-filled iPP composites mainly crystallized in α-spherulite and β-wollastonite-filled iPP composites formed β-spherulite. In addition, the spherulite size of β-wollastonite-filled iPP composites was smaller than that of α-wollastonite-filled iPP composites. Jeziorny and Mo methods were applicable to study the non-isothermal crystallization kinetics of wollastonite-filled iPP composites. The activation energy (?E) and the nucleation efficiency (EN) of non-isothermal crystallization were calculated by Kissinger method and the equation proposed by Fillon, respectively. The β-wollastonite-filled iPP composites exhibited higher crystallization rate, activation energy, and EN than that of α-wollastonite-filled iPP composites.     

Nonisothermal crystallization kinetics of polypropylene/montmorillonite nanocomposites

The nonisothermal crystallization kinetics of poly(propylene) (PP) and poly(propylene)/organic‐montmorillonite (PP/Mont) nanocomposite were investigated by differential scanning calorimetry (DSC) with various cooling rates. The Avrami analysis modified by previous research was used to describe the nonisothermal crystallization process of PP and PP/Mont nanocomposite very well. The values of half‐time and Z_c showed that the crystallization rate increased with increasing cooling rates for both PP and PP/Mont nanocomposite, but the crystallization rate of PP/Mont nanocomposite was faster than that of PP at a given cooling rate. The activation energies were estimated by the Kissinger method, and the values were 189.4 and 155.7 kJ/mol for PP and PP/Mont nanocomposite, respectively. PP/Mont nanocomposite could be easily fabricated as original PP, although the addition of organomontmorillonite might accelerate the overall nonisothermal crystallization process. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 408–414, 2002; DOI 10.1002/polb.10101     

Crystallization kinetics of polyethylene/paraffin oil blend sheets formed by thermally induced phase separation with different molecular weights of polyethylene

Polyethylene/paraffin oil blend sheets with different molecular weights of polyethylene were prepared by thermally induced phase separation. Isothermal and non-isothermal crystallization behaviors of blend sheets were investigated by differential scanning calorimetry (DSC). Isothermal DSC curves were analyzed by Avrami equation, whereas non-isothermal DSC curves were analyzed by Jeziorny method and Mo method. Effective activation energy (ΔE) of isothermal and non-isothermal crystallization was calculated by Friedman method. Under isothermal condition, value of n in Avrami equation hovered at 2.1, and lgZ increased with the decrease of crystallization temperature. lgZ and ΔE of blend sheets with a larger molecular weight of polyethylene was smaller than that of blend sheets with smaller molecular weight. Under non-isothermal condition, value of n obtained by Jeziorny method hovered at 2.4, close to n of isothermal condition. lgZ _c increased with the increase of cooling rate and decrease of molecular weight of polyethylene. ΔE of different blend sheets were close to each other. Crystal structures of blend sheets formed under non-isothermal condition were analyzed by X-ray diffraction (XRD) analysis. XRD analysis showed that molecular weight of polyethylene and cooling rate had slight influence on crystal structure and crystallinity of polyethylene/paraffin oil blend sheet.     

水性聚氨酯/功能化石墨烯纳米复合材料的非等温结晶动力学

采用差示扫描量热法DSC研究了水性聚氨酯/功能化石墨烯(WPU/FGNs)纳米复合材料的非等温结晶行为,分别采用Ozawa方程、莫志深方程研究复合材料的非等温结晶动力学,并通过Kissinger方程计算了结晶过程中的活化能。 结果表明,石墨烯在复合材料的结晶过程中起到异相成核剂的作用,提高了复合材料的结晶起始温度、峰值温度和结晶速率;增加石墨烯的质量分数,复合材料的结晶维数增加;石墨烯增加至0.3%,复合材料的活化能从-47.74 kJ/mol降低至-53.60 kJ/mol,继续增加石墨烯至1.0%,复合材料的活化能增加至-41.74 kJ/mol。     

Effect of Electron Beam Irradiation on the Kinetics of Non-isothermal Crystallization of Nylon 66

The non-isothermal crystallization kinetics was studied by differential scanning calorimetric analysis on nylon 66 and e-beam irradiated nylon 66 at different cooling rates. The Modified Avrami equation, the Ozawa equation and the Combined Avrami-Ozawa equation were applied to study the kinetics of non-isothermal crystallization of nylon 66. The crystallization behavior of pristine nylon 66 polymer was compared with that of e-beam irradiated nylon 66 and observed that the kinetics of non-isothermal crystallization of nylon66 was affected largely upon e-beam irradiation. E-beam irradiation not only decreased the crystallization temperature of nylon 66, but influenced the mechanism of nucleation and crystal growth and reduced the overall crystallization rate of nylon 66 also. The crystallization activation energy calculated by the Kissinger method for irradiated nylon 66 was lower than that of pristine nylon 66.     

Non-isothermal crystallization kinetics of β-nucleated isotactic polypropylene

Isotactic polypropylenes (iPP) samples were incorporated with two β-nucleating agents (NT-A and NT-C), respectively, and their non-isothermal crystallization and subsequent melt behaviors were investigated by means of differential scanning calorimeter. Jeziorny, Ozawa, and Mo methods were used to analyze non-isothermal crystallization kinetics of pure iPP and β-nucleated iPP samples. The activation energies (ΔE) of non-isothermal crystallization were calculated by Kissinger method. And the nucleation activities were calculated according to the Dobreva method. It is found that the crystallization temperature decreases and the crystallization rate increases with increasing cooling rate. The crystallization temperature and crystallization rate of nucleated iPP are higher than those of pure iPP. The order of ΔE is NT-A/iPP > pure iPP > NT-C/iPP. NT-C is more efficient than NT-A as a β-nucleating agent. But the non-isothermal crystallization kinetics of α- and β-phases cannot be determined separately. The present results should be considered with caution.     

苯乙烯-丙烯等规立构嵌段共聚物(iPS-b-iPP)的非等温结晶动力学的研究

用DSC法研究了苯乙烯-丙烯等规立构嵌段共聚物的非等温结晶动力学。结果表明:冷却速率在5～20℃/min范围内,共聚物的非等温结晶动力学参数能很好地符合Avrami动力学方程,非等温结晶速率常数与冷却速率有关,动力学结晶能力则同时受到冷却速率和共聚物组成比的影响。文中还讨论了在非等温结晶条件下共聚物的结晶成核和生长方式与共聚物组成和结构的关系。联合Avrami方程和Ozawa方程推导的非等温结晶动力学方程较好地描述了iPS-b-iPP嵌段共聚物的非等温结晶动力学过程。     

一种典型半结晶型聚酰亚胺的非等温结晶动力学

使用3,3 ′,4,4′-联苯四酸二酐( s-BPDA),1,3,-双(4-氨基苯氧基)苯(TPER)和苯酐(PA)反应合成了一种半结晶型聚酰亚胺.根据DSC记录的不同速率下降温所得到的结晶放热曲线,分别采用Jeziorny、Ozawa及奠志深提出的方法对其非等温结晶行为进行了研究.发现由Jeziorny方法分析得到的...     

聚乳酸的非等温结晶行为

用差示扫描量热法(DSC)研究聚乳酸(PLA)从熔体及玻璃态为初始条件下的非等温结晶行为,采用Ozawa方程、Mo法、Khanna法和Kissinger法对结晶动力学参数进行计算处理。 实验结果表明,这几种方法均适合处理PLA的非等温结晶过程,而Khanna法提出的结晶速率系数(CRC)能够方便地评价PLA相对结晶速率的大小。 PLA从玻璃态升温结晶比从熔体降温结晶容易得多,升温过程有利于晶核生成,而降温有利于晶体生长。 升温结晶时,升温速率2.0 ℃/min时,结晶焓(ΔH_c)达到最大为27.1 J/g。 从熔体等速降温过程中,随着冷却速率的降低ΔH_c单调增加,冷却速率为0.25 ℃/min时ΔH_c增加到28.3 J/g。 在较低温度下从玻璃态结晶,主要表现为异相成核的二维生长方式。 在较高的温度下从玻璃态升温结晶及从熔体冷却结晶时,以均相成核的三维生长方式结晶为主。 与升温过程相比,冷却不利于晶核的生成,所以导致冷却过程总体ΔH_c偏低,扩散活化能偏大。