Characterization of a maleic anhydride-modified polypropylene as an adhesion promoter for glass fiber composites

Isothermal and nonisothermal crystallizations of isotactic polypropylene (iPP), maleic anhydride (MAH)-grafted PP, and MAH-modified iPP were studied by differential scanning calorimetry (DSC), to evaluate the influence of a small amount of MAH-grafted PP in iPP on its crystallization behavior. Isothermal crystallization was followed in the temperature range from 391 K to 403 K, and the rate constant and Avrami exponents were determined. Nonisothermal crystallization was carried out at different cooling rates (1-20 K/min). It was found that the crystallization kinetics of iPP was significantly altered by modification with the MAH-grafted polymer. A decreased equilibrium melting temperature, as well as decreased surface energy of folding and critical dimensions of a growing nucleus, was determined for the MAH-modified iPP, indicating faster growth of lamellae and a higher rate of crystallization. The improved nucleation ability of the modified polymer was shown to cause a shift in the crystallization peak temperature towards higher values (from 393.7 K to 399.6 K, at a cooling rate of 1 K/min), resulting in crystal structures less disposed to recrystallization. Model composites of iPP and MAH-modified iPP with glass fibers were also analysed. The apparent shear strength of single-fiber model composites with MAH-modified iPP was drastically increased compared with homo-iPP.     

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

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

Stereochemical composition-properties relationships in isotactic polypropylenes obtained with different catalyst systems

The influence of stereochemical composition of the radial growth rate of spherulites, the nucleation density, the overall rate of crystallization and the thermal behaviour of fractions of iPP samples synthesized with different catalyst systems (low, high and very high yield) was investigated. The study used ¹³C n.m.r., differential scanning calorimetry (d.s.c.) and optical microscopy. The ¹³C n.m.r. analysis showed that due to the presence of catalytic sites with different stereoregulating capability the catalyst system produces polypropylene with different stereoregularity. It was found that the growth rate of spherulites and the overall rate of crystallization are strictly related to the stereochemical structure of the polypropylene. Moreover, for the low yield iPP, phenomena of secondary crystallization were observed by Avrami analysis of the overall kinetics. Values of the equilibrium melting temperature (T_m), energy of nucleation (Δø1) and surface free energy of folding (σe) of iPP lamellar crystals have been determined according to the kinetic theory of polymer crystallization. The values of such thermodynamic quantities as well as the thermal behaviour of various iPP are strongly dependent upon the amount and distribution of configurational irregularities existing along the chains and upon the molecular mass distribution.     

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

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

Effect of silicon dioxide on crystallization and melting behavior of polypropylene

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

The influence of rubber-matrix interfaces on the crystallization kinetics of isotactic polypropylene blended with ethylene-propylene-diene terpolymer (EPDM)

Blends of isotactic polypropylene with amorphous and slightly crystalline ethylene-propylene-diene terpolymer (EPDM), prepared by solution blending, have been investigated by optical microscopy and differential scanning calorimetry. Nucleation and crystallization kinetic parameters, such as nucleation rates, nucleation half times, Avrami-exponents and spherulitic growth rates, have been determined. It has been found that the dispersion of crystalline EPDM in iPP is different from that of amorphous EPDM. Both EPDMs are incorporated into the spherulites, causing a decrease of the maximum growth rate of the iPP spherulites. The surface free energy of the iPP crystals is diminished on adding EPDM to iPP and is accompanied by a higher secondary nucleation rate. From the decrease observed in the Avrami exponent with increasing EPDM concentration in the blend, it has been concluded that nucleation becomes predominantly heterogeneous, as there is a proportional increase in the interfacial area between the two components.     

Effects of liquid–liquid phase separation on crystallization kinetics and morphology of isotactic polypropylene/poly (ethylene-co-octene) in-reactor alloy

In this work, we investigated the effects of liquid–liquid phase separation (LLPS) on the crystallization kinetics and morphology of isotactic polypropylene/poly (ethylene-co-octene) (iPP/PEOc) in-reactor alloy with polarized optical microscopy (POM), differential scanning calorimeter (DSC), scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS) methods. Based on crystallization kinetics analysis by Avrami equation, we found that the overall crystallization rate was almost independent on LLPS time, whereas was strongly dependent on crystallization temperature. However, by combination with POM, we found that the LLPS played two opposite roles on the overall crystallization rate, i.e. the nucleation rate decreased and the spherulite growth rate increased as increasing LLPS time. It is due to the nucleation rate was dominated by fluctuation-assisted nucleation mechanism and the growth rate was dominated by diffusion-controlled growth. Furthermore, the spherulite size and PEOc domain size of iPP/PEOc in-reactor alloy were significantly dependent on LLPS time; however, the crystallinity was almost not dependent on LLPS time.     

石墨烯对聚苯硫醚非等温结晶行为的影响研究

通过熔融共混法制备了聚苯硫醚(PPS)/石墨烯(G)复合材料,采用扫描电子显微镜、差示扫描量热仪研究了PPS/G复合材料的断面形貌及非等温结晶过程,利用莫志深方程、Dobreva方程和Kissinger方程分析了非等温结晶动力学行为。结果表明:石墨烯质量分数低于0.5%时,其在PPS基体中具有较好的分散性;石墨烯起到了异相成核作用,使PPS/G程、Dobreva方程和Kissinger方程则进一步验证了石墨烯的引入促进了PPS/G复合材料的结晶。     

Crystallization of isotactic polypropylene inside dense networks of carbon nanofillers

In this study, we performed the crystallization of carbon nanotube (CNT)/isotactic polypropylene (iPP) and graphene nanosheet (GNS)/iPP composites with very high nanofiller loadings; these are frequently used in polymer composites for electromagnetic interference shielding and thermal conductivity. Rheology testing indicated that both the high‐loading CNTs and GNSs formed dense networks in the iPP matrix, and transmission electron microscopy showed that their connection types were completely different: the CNTs contacted one another in a dot‐to‐dot manner, whereas the GNSs linked reciprocally in a plane‐to‐plane manner. The carbon nanofiller networks brought about two opposite effects on iPP crystallization: a nucleation effect and a confinement effect. The CNT network showed a stronger nucleation effect; however, the CNT network also revealed a more powerful confinement effect because the CNT network was denser than the GNS network. With increasing content of the carbon nanofillers, the crystallization rates of both the CNT and GNS composites first increased, then decreased, and showed a very high saturation concentration at 50 wt %; this resulted from the competitive relationship between the nucleation effect and confinement effect. The crystallization was facilitated when the carbon nanofiller concentration was below saturation, where the nucleation effect invariably played a dominant role. Although the crystallization was depressed when the carbon nanofiller concentration was above saturation, the nucleation effect was subdued, and the confinement effect was extensive. Compared to the GNS/iPP composites, the CNT/iPP composites showed a more depressed crystallization. The suppression mechanism is discussed with consideration of the local topological structure constructed by those two carbon nanofillers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39505.     

Isothermal crystallization kinetics of in situ Nylon 6/graphene composites by differential scanning calorimetry

The isothermal crystallization kinetics of nylon 6/graphene (NG) composites prepared by in situ polymerization was investigated by differential scanning calorimetry. The Avrami equation was used to study the crystallization kinetics. Comparing with nylon 6, it is found that the NG composites (NG‐0.1, NG‐0.5, and NG‐1.0, where the number describes the wt% content of graphene) had higher crystallization rates; the crystallization rate increased remarkably with 0.1 wt% graphene. However, too many crystallization nuclei could not accelerate the crystallization process effectively. The t_max values obtained from the plots of heat flow versus time were in agreement with the t_max values calculated from the half time of crystallization when the graphene content was lower than 1.0 wt%, which means that the values of the Avrami parameters calculated from the half time of crystallization might be in better agreement with the actual crystallization mechanism than that determined from the Avrami plots. The n values of the NG composites ranged between 1.1 and 1.8, which can be interpreted as meaning both one‐dimensional and two‐dimensional crystallization growth occurred during isothermal crystallization process. The activation energies, which were determined by the Arrhenius' method, varied within the range from ?188 to ?142 kJ/mol. POLYM. ENG. SCI., 54:2610–2616, 2014. © 2013 Society of Plastics Engineers     

Temperature dependence of the nucleation effect of sorbitol derivatives on polypropylene crystallization

The temperature dependence of the nucleation effect of three sorbitol derivatives on the crystallization of isotactic polypropylene (iPP) was studied by means of isothermal crystallization kinetic analysis. Isothermal crystallization thermograms obtained by differential scanning calorimetry (DSC) were analyzed based on the Avrami equation. The Avrami analysis for the nucleated iPP was carried out with DSC data collected to 35% relative crystallinity, and the rate constants were corrected assuming the heterogeneous nucleation and three dimensional growth of iPP spherulites. A semi-empirical equation for the radial growth rate of iPP spherulites was given as a function of temperature and was used to determine the number of effective nuclei at different temperatures. The number of effective nuclei in the nucleated samples was estimated to be 3 × 10² ∽ 10⁵ times larger than that in the neat iPP. The logarithmic numbers of the effective nuclei decreased linearly with decreasing degree of supercooling in the range of crystallization temperatures tested. The temperature dependence of the effect of the nucleating agents on iPP crystallization was given quantitatively in terms of the deactivation factor defined as a fraction of the particles that are active at a particular temperature but inert at the temperature one degree higher. The nucleation activity and its temperature dependence are considered to be cooperative effects of many factors, including the dispersion and the physical or chemical nature of the agent as well as the interaction between the agent and the polymer. It is suggested that the temperature dependence of the effect of a nucleating agent should be treated as a characteristic of a given polymer/ nucleating agent mixture.     

Kinetics of growth of spinel crystals in a borosilicate glass

Three aspects of the kinetics of spinel crystallization in a high-level waste (HLW) glass were studied: (1) the effect of nucleation agents on the number density (n_s) of spinel crystals, (2) crystallization kinetics in a crushed glass, and (3) crystallization kinetics in a glass preheated at T>T_L (liquidus temperature). In glass lacking in nucleation agents, n_s was a strong function of temperature. In glasses with noble metals (Rh, Ru, Pd, and Pt), n_s increased by up to four orders of magnitude and was nearly independent of temperature. The kinetics of spinel crystallization in crushed glass lacking nucleation agents was dominated by surface crystallization and was described by the Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation with the Avrami exponent n≅0.5. For application to HLW glass melter processing, it was necessary to preheat glass at T>T_L to eliminate the impact of temperature history and surface crystallization on crystal nucleation and growth. In the temperature range of glass processing, crystals descend under gravity when they reach a critical size. Below this critical size, crystallization kinetics is described by the KJMA equation and above the critical size by the Hixson-Crowell equation. At low temperatures, at which glass viscosity is high and diffusion is slow, the KJMA equation represents crystal growth from nucleation to equilibrium. As n_s increases, the temperature interval of the transition from the KJMA to Hixson-Crowell regime shifts to a higher temperature.     

Crystallization morphologies and non-isothermal crystallization kinetics of isotactic polypropylene modified by α/β compounded nucleating agents

采用偏光显微镜(POM)及示差扫描量热(DSC)法考察了3种α/β复合成核剂NA40/NABW、NA40/HHPA-Ba、NA40/PA-03对成核等规聚丙烯(iPP)的结晶形态及非等温结晶动力学的影响。对成核iPP结晶形态的研究结果表明：α/β复合成核剂的加入能够减小iPP的球晶尺寸。影响α/β复合成核剂成核iPP结晶形态的主要因素是ΔT_Cp（ΔT_Cp为成核iPP结晶峰值温度与iPP结晶峰值温度的差值）,即复合体系中ΔT_Cp较大的成核剂在iPP结晶过程中起主导作用,最终的结晶形态与单独添加这一成核剂时iPP的结晶形态相类似;当两种成核剂的ΔT_Cp接近相同时,两者竞争成核,成核iPP的结晶形态表现为两种成核剂共同作用的结果。因此,通过改变α/β复合成核剂的复合比例即改变两种成核剂的添加浓度,进而改变其ΔT_Cp,可以得到结晶形态完全不同的iPP。采用Caze法对非等温动力学进行了研究,结果表明：添加α/β复合成核剂能够提高iPP的结晶温度,缩短半结晶时间。复合成核剂成核iPP的结晶行为也同样受成核剂ΔT_Cp的影响,复合成核iPP的Avrami指数接近于复合体系中ΔT_Cp较大的成核剂单独添加时iPP的Avrami指数。     

Effects of dodecyl amine functionalized graphene oxide on the crystallization behavior of isotactic polypropylene

Dodecyl amine functionalized graphene oxide (DA‐GO)/isotactic polypropylene (iPP) nanocomposites were prepared via solution mixing method. Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and X‐ray photoelectron spectroscopy (XPS) verified that the DA was successfully grafted onto the surface of graphene oxide. The crystallization behavior of iPP/DA‐GO nanocomposites was investigated by differential scanning calorimetry (DSC) and polarized optical microscope (POM). The DSC results of both isothermal and non‐isothermal crystallization process indicated that the addition of DA‐GO can decrease the half‐time crystallization (t_1/2) and elevate crystallization peak temperature (T_p) of iPP. The results of isothermal crystallization kinetics showed that the overall crystallization rates of iPP/DA‐GO nanocomposites, especially with higher DA‐GO content, were much faster than that of neat iPP. During the non‐isothermal crystallization process, the nucleation ability (Φ) of nanocomposites containing 0.05, and 0.5 wt % DA‐GO were 0.83 and 0.69, respectively. And the crystallization activation energy of iPP decreased from 348.7 (neat iPP) to 309.2 and 283.1 kJ/m 2 by addition of 0.05 and 0.5 wt % DA‐GO, respectively. The decrease of Φ and indicated DA‐GO has strong heterogeneous nucleation effect and can promote the crystallization of iPP significantly. Additionally, POM micrographs showed the DA‐GO in iPP matrix can form more nucleation sites for the spherulite growth. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40000.     

Effects of reinforcing fibers on the crystallization of polypropylene

The effects of the incorporation of different types of fibers on the crystallization kinetics and thermodynamics of isotactic polypropylene (iPP) are investigated. The study is mainly performed by thermal analysis, both in isothermal and constant cooling rate conditions, utilizing differential scanning calorimetry (DSC). The crystallization kinetics of the studied composites is successfully described by the Avrami model. Moreover, the effects of different kind of fibers are studied comparing the values of kinetics parameters such as the Avrami exponent n, the kinetic constant of the crystallization rate, Kn and the half‐time of crystallization, T 1/2. The results of the investigation show that the fibers behave as effective nucleant agents for the crystallization of polypropylene. In fact, a dramatic decrease of the half‐time of crystallization, T1/2, as well as a sensible increase of the overall crystallization rate, Kn, are observed in the presence of all the fibers analyzed. These effects are more marked in the presence of aramid fibers. The Avrami model is successfully applied to describe the crystallization kinetics of the composites. The kinetic curves obtained under non‐isothermal conditions confirm the results obtained under isothermal conditions and demonstrate the nucleating action of the fibers on the PP crystallization. Furthermore, the spherulite growth and the transcrystallinity on the surface of the fibers are investigated by optical polarizing microscopy. It is observed that transcrystallinity takes place in all kind of fibers studied, but also in this case, aramid fibers are the most effective in promoting transcrystallinity.     

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

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

Miscibility in crystalline polymer blends: Isotactic polypropylene and linear low‐density polyethylene

The phase behavior and the crystallization kinetics of blends composed of isotactic polypropylene (iPP) and linear low‐density polyethylene (LLDPE) were investigated by differential scanning calorimetry. The phase behavior indicates the formation of separate crystals of iPP and LLDPE at each investigated blend composition. The crystallization trace reveals that iPP crystallizes in its normal range of temperatures (i.e., at temperatures higher than that of LLDPE), when its content in the blend is higher than 25% by weight. In the blend whose iPP content is as high as 25%, at least a portion of iPP crystallizes at temperatures lower than that of LLDPE. This behavior has been proposed by Bassett to be attributed to a change in the kind of nucleation from heterogeneous to homogeneous. From the Avrami analysis of the isothermal crystallization of iPP in the presence of molten LLDPE, n values close to 2 are always obtained. According to our previously proposed interpretation of the Avrami coefficient, it can be related to the crystallite fractal dimension, through d = n + 1, which gives values close to 3, according to the spherulitic observed morphology. The kinetics parameter, i.e., the half‐time of crystallization, and the kinetic constant k show that a decrease in the overall rate of crystallization of iPP occurs on blending. Optical microscopy photographs, taken during the cooling of the samples from the melt, confirm the above results and show increasingly less resolved spherulite texture on increasing LLDPE content in the blend. The diffusion parameters evaluated for the neat polymers and for the blends in dichloromethane, which give information on the miscibility in the amorphous state, show that the diffusional behavior of the blends is governed by iPP, suggesting a two‐phase amorphous state. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3338–3346, 2003     

α/β复合成核剂对等规聚丙烯结晶形态的影响及非等温结晶动力学

采用偏光显微镜(POM)及示差扫描量热(DSC)法考察了3种α/β复合成核剂NA40/NABW、NA40/HHPA-Ba、NA40/PA-03对成核等规聚丙烯(iPP)的结晶形态及非等温结晶动力学的影响。对成核iPP结晶形态的研究结果表明：α/β复合成核剂的加入能够减小iPP的球晶尺寸。影响α/β复合成核剂成核iPP结晶形态的主要因素是ΔT_Cp（ΔT_Cp为成核iPP结晶峰值温度与iPP结晶峰值温度的差值）,即复合体系中ΔT_Cp较大的成核剂在iPP结晶过程中起主导作用,最终的结晶形态与单独添加这一成核剂时iPP的结晶形态相类似;当两种成核剂的ΔT_Cp接近相同时,两者竞争成核,成核iPP的结晶形态表现为两种成核剂共同作用的结果。因此,通过改变α/β复合成核剂的复合比例即改变两种成核剂的添加浓度,进而改变其ΔT_Cp,可以得到结晶形态完全不同的iPP。采用Caze法对非等温动力学进行了研究,结果表明：添加α/β复合成核剂能够提高iPP的结晶温度,缩短半结晶时间。复合成核剂成核iPP的结晶行为也同样受成核剂ΔT_Cp的影响,复合成核iPP的Avrami指数接近于复合体系中ΔT_Cp较大的成核剂单独添加时iPP的Avrami指数。     

PP/PP-g-NH2/纳米SiO2复合材料的非等温结晶

采用示差扫描量热法（DSC）研究了聚丙烯/氨基化聚丙烯/纳米二氧化硅（PP/PP-g-NH₂/SiO₂）复合材料的非等温结晶行为。利用Caze法对结晶动力学进行了分析,Avrami指数n表明纳米SiO₂和PP-g-NH₂的加入改变了PP的结晶成核和生长机理;运用Dobreva法研究了纳米粒子的成核活性,结果表明纳米SiO₂成核活性差,增容剂PP-g-NH₂明显增强其成核活性;采用Friedman法分析了复合材料的结晶有效能垒,研究表明加入纳米SiO₂使PP的结晶有效能垒降低,添加PP-g-NH₂则进一步降低复合体系的结晶有效能垒;当纳米粒子含量为3%时,添加5% PP-g-NH₂能有效提高纳米粒子成核活性,降低复合材料结晶有效能垒。