Synthesis and Thermal Behavior of Silica‐Graft‐Polypropylene Nanocomposites Studied by Step‐Scan DSC and TGA

Silica graft poly(propylene) (silica‐g‐PP) nanocomposites were successfully prepared by radical grafting copolymerization and ring‐opening reaction. Their thermal properties were studied by step‐scan differential scanning calorimetry (SDSC) and thermogravimetric analysis (TGA). The exothermic peaks in the IsoK baseline (C_p,IsoK, nonreversing signal) of SDSC reveal that PP and silica‐g‐PP nanocomposites undergo melting‐recrystallization‐remelting during heating. The peak temperatures of recrystallization and remelting shift upward with the existence of nanoparticles in the PP matrix. The thermal degradation kinetics of silica‐g‐PP nanocomposites were investigated using nonisothermal TGA and the Flynn‐Wall‐Ozawa method. The results indicate that the thermal stability was significantly improved with increasing silica content, mainly because of the physical‐chemical adsorption of the volatile degradation products on the nanoparticles that delays their volatilization during decomposition, and the covalent interaction between nanoparticles and PP chains, which will also reduce the breakage of PP backbone chains.     

A Kinetic Study of the Thermal Degradation of Nylon-6/Attapulgite Nanocomposites

The thermal degradation behavior of nylon-6 (PA6) and PA6/attapulgite (ATP) nanocomposites was investigated by thermogravimetric analysis under non-isothermal conditions at various heating rates in nitrogen. It is suggested that during thermal degradation, ATP, as a protective barrier, can slow down degradation of polymer, but the catalytic effects of structural water and hydroxyl groups may accelerate the degradation of PA6. The combination of these two effects determined the final thermal stability of nanocomposites. The apparent activation energies of the samples were evaluated by the Kissinger and Flynn–Wall–Ozawa methods. The results showed that the presence of ATP adversely affected the thermal stability of PA6. The degradation activation energies of PA6/ATP nanocomposites decreased monotonically with increase in ATP content; thus, it is suggested that the ATP has a disadvantageous effect on the thermal stability of PA6.     

Nonisothermal Crystallization Behavior of Polypropylene-C60 Nanocomposites

The nonisothermal crystallization behavior of polypropylene (PP) and PP-fullerene (C₆₀) nanocomposites was studied by differential scanning calorimetry (DSC). The kinetic models based on the Jeziorny, Ozawa, and Mo methods were used to analyze the nonisothermal crystallization process. The onset crystallization temperature (T_c), half-time for the crystallization (t_1/2), kinetic parameter (F(T)) by the Mo method and activation energy (ΔE) estimated by the Kissinger method showed that C₆₀ accelerates the crystallization of PP, implying a nucleating role of C₆₀. Furthermore, due to the reduced viscosity of PP by adding 5% C₆₀, the parameters of crystallization kinetics for the PP-5%C₆₀ nanocomposites changed remarkably relative to that of neat PP and when lower contents of C₆₀ were added to PP.     

The Effect of Zinc Oxide and Calcium Carbonate Nanoparticles on the Thermal Conductivity of Polypropylene

The thermal conductivity (TC) of compression-moulded polypropylene (PP) and PP filled with 5–15% zinc oxide (ZnO) or calcium carbonate (CaCO₃) nanoparticles, prepared by extrusion, was studied using a thermal conductivity analyzer (TCA). The effect of nanoparticle content and crystallinity on the thermal conductivity was investigated using conventional methods, including SEM, XRD, and DSC. The incorporation of nanoparticles improved the crystallinity and thermal conductivity simultaneously. The experimental TC values of the PP nanocomposites with different level of nanoparticles concentration showed a linear increase with an increase in crystallinity. The TC improvement in PP/ZnO nanocomposite was greater than that of PP/calcium carbonate nanocomposites. This fact can be attributed to the intrinsic, better thermal conductivity of the ZnO nanoparticles. Several models were used for prediction of the TC in the nanocomposites. In the PP/ZnO nanocomposites the TC values correlated well with the values predicted by the Series, Maxwell, Lewis and Nielson, Bruggeman, and De Loor models up to 10 wt%.     

Thermal Behavior of Polypropylene-g-glycidyl Methacrylate Prepared by Melt Grafting

The thermal behaviors of glycidyl methacrylate (GMA)-grafted polypropylene (PP) (PP-g-GMA) with two different grafting degrees, namely, GPP1 and GPP2, were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray diffraction (WAXD), dynamic mechanical analysis (DMA), and thermogravimetrical analysis (TGA). DSC results suggested that the GMA grafted PP exhibited higher crystallization temperature T_c, higher melting temperature T_m, and higher crystallinity compared with the neat PP. The isothermal crystallization kinetics was analyzed with the Avrami equation and the total crystallization activation energy was calculated. It was concluded that the crystallization processes of PP and the grafted PP were controlled by nucleation and the values of the crystallization activation energy of PP and the grafted PP were almost identical. POM results suggested that the GMA grafted PP exhibited smaller spherulites size compared with the neat PP. WAXD patterns indicated that the neat PP encouraged the formation of γ phase, compared with the grafted PP, during the crystallization process. DMA results showed that melt grafting did not induce a clear effect on the γ-transition and β-transition of the amorphous phase but resulted in a decrease in mobility of the PP chains in the crystals. TGA curves suggested that the melt grafting slightly improved the thermal stability of PP.     

Thermo-oxidative degradation kinetics of grafted polypropylene films

The thermo-oxidative stability and degradation behavior of polypropylene (PP) and grafted PP have been investigated using thermogravimetric analysis. Three multiple heating rate methods, namely Kissinger, Kim–Park and Flynn–Wall have been used to calculate the activation energy as a function of the extent of degradation. The four different heating rates (5, 10, 15 and 20°C/min) were maintained in the temperature range of 30–550°C during the analysis. Fourier transform infrared spectroscopy has confirmed the presence of carboxylic group on the surface of grafted PP films. Differential scanning calorimetry has shown that the crystallinity decreased with the increase in grafting. In the air atmosphere, the thermo-oxidative degradation occurs via a pathway that involves decomposition of polymer peroxide. Thermo-oxidative stability of grafted PP films is found to increase with an increase in the degree of grafting (DG). The degradation kinetic parameters were used to predict the lifetime of PP and grafted PP films. The activation energy and lifetime of grafted PP films increased with an increase in the DG. The lifetime of PP and grafted PP decreased with an increase in degradation temperature.     

Composites from Brazilian natural fibers with polypropylene: mechanical and thermal properties

Brazil has a well established ethanol production program based on sugarcane. Sugarcane bagasse and straw are the main by-products that may be used as reinforcement in natural fiber composites. Current work evaluated the influence of fiber insertion within a polypropylene (PP) matrix by tensile, TGA and DSC measurements. Thus, the mechanical properties, weight loss, degradation, melting and crystallization temperatures, heat of melting and crystallization and percentage of crystallinity were attained. Fiber insertion in the matrix improved the tensile modulus and changed the thermal stability of composites (intermediary between neat fibers and PP). The incorporation of natural fibers in PP promoted also apparent T _c and ΔH _c increases. As a conclusion, the fibers added to polypropylene increased the nucleating ability, accelerating the crystallization process, improving the mechanical properties and consequently the fiber/matrix interaction.     

Investigation on Properties of Polypropylene/Multi-walled Carbon Nanotubes Nanocomposites Prepared by a Novel Eccentric Rotor Extruder Based on Elongational Rheology

The properties of polymer matrix composites are related not only to the chemical composition of the materials but also to the processing equipment used for their preparation which has a direct influence on the microstructure of the composites. In this paper polypropylene (PP)/multi-walled carbon nanotubes (MWCNTs) nanocomposites were prepared by melt blending through a self-developed, eccentric rotor extruder (ERE). The structure and elongational deformation mechanism of an ERE were described in detail. The morphological, rheological, thermal and mechanical properties of the resulting PP/MWCNTs nanocomposites were investigated. Scanning electron microscopy (SEM) and rheological analysis showed that the MWCNTs were well dispersed in the PP matrix. The thermal stability was investigated by thermogravimetric analysis (TGA) and indicated that the addition of MWCNTs could effectively improve the thermal stability of pure PP. The percentage of crystallinity and tensile strength of the composites were improved as a result of the heterogeneous nucleation effect of the MWCNTs in the PP matrix. The research results revealed that the enhancement of the properties of PP/MWCNTs composites could be attributed to a better dispersion of the MWCNTs in the matrix as compared to samples prepared by conventional extrusion.     

Effects of Montmorillonite on the Nonisothermal Crystallization Behavior of the Poly(trimethylene terephthalate)/Polypropylene/Montmorillonite Nanocomposites

Organic montmorillonite (MMT) reinforced poly(trimethylene terephthalate) (PTT)/ polypropylene (PP) nanocomposites were prepared by melt blending. The effects of MMT on the nonisothermal crystallization of the matrix polymers were investigated using differential scanning colorimetry (DSC) and analyzed by the Avrami equation. The DSC results indicated that the effects of MMT on the crystallization processes of the two polymers exhibited great disparity. The PTT's crystallization was accelerated significantly by MMT no matter whether PTT was the continuous phase or not, but the thermal nucleation mode and three-dimensional growth mechanism remained unchanged. However, in the presence of MMT, the PP's crystallization was slightly retarded with PP as the dispersed phase, and was influenced little with PTT as the dispersed phase. When the MMT content was increased from 2_wt% to 7_wt%, the crystallization of the PTT phase was slightly accelerated, whereas the crystallization of the PP phase was severely retarded, especially at lower temperatures. Moreover, the nucleation mechanism for the PP's crystallization changed from a thermal mode to an athermal one. In the polypropylene-graft-maleic anhydride (PP-g-MAH) compatibilized PTT/PP blends, with the addition of 2_wt% MMT during melt blending, the T _c (PTT) shifted 7.8°C to lower temperature and had a broadened exotherm, whereas the T _c (PP) shifted 17.1°C to higher temperature, with a narrowed exotherm. TEM analysis confirmed that part of the PP-g-MAH was combined with MMT during blending.     

多壁碳纳米管/聚丙烯复合材料热导率研究

用Pt细丝代替已有3ω方法中的薄膜热线,并设计了基于Labview程序的虚拟测量系统,准确、方便地测量了聚丙烯复合材料的热导率. 测量结果发现,多壁碳纳米管/丁苯橡胶/聚丙烯三元复合材料的热导率随着多壁碳纳米管/丁苯橡胶粉末含量的增加变化不大;多壁碳纳米管/聚丙烯复合材料的热导率随着多壁碳纳米管含量增加而增大;复合材料热导率远小于简单混合规则预测的结果,而与有效介质理论符合很好. 关键词： ω法')" href="#">3ω法 多壁碳纳米管 聚丙烯复合材料 热导率     

Isothermal Crystallization and Subsequent Melting Behavior of Poly(ethylene terephthalate)/Silica Nanocomposites

The crystallization process of poly(ethylene terephthalate)/silica nanocomposites were investigated by differential scanning calorimetry (DSC) and then analyzed using the Avrami method. The results indicated that the crystallization of pure poly(ethylene terephthalate) (PET) was fitted for thermal nucleation and three‐dimensional spherical growth throughout the whole process, whereas the crystallization of PET/silica nanocomposites exhibits two stages. The first stage corresponds to athermal nucleation and three‐dimensional spherical growth, and the second stage corresponds to recrystallization caused by the earlier spherulites impingement. The crystallization rate increases remarkably and the activation energies decrease considerably when silica nanoparticles are added. The subsequent melting behavior of the crystallized samples shows that the melting point (T _m) of nanocomposites is higher than that of pure PET, which might be caused by two factors: (1) The higher melting point might be due to some hindrance to the PET chains caused by the nanoparticles at the beginning of the melting process; (2) it might also be the case that more perfect crystals can be formed due to the higher crystallization temperatures and lower activation energies of PET/silica nanocomposites.     

Thermal and Tribological Properties of Fullerene‐Containing Composite Systems. Part 3. Features of the Mechanism of Thermal Degradation of Poly‐(N‐Vinyl‐Pyrrolidone) and Its Compositions with Fullerene C60

By mass‐spectrometric thermal analysis (MTA) the thermochemical features of poly(N‐vinyl pyrrolidone) (PVP) and its compositions with fullerene C₆₀ were studied. The mechanism of PVP thermal degradation was investigated; in particular the nature of the low‐temperature degradation (between 75 and 300°C) accompanied by output of pyrrolidone was explained as well as the influence of fullerene C₆₀ on this mechanism. It was shown that during thermal degradation of copolymer PVP‐C₆₀, there is a disappearance of the low‐temperature peaks of the output of pyrrolidone that is interpreted as an increase of the thermal stability of N‐vinyl‐pyrrolidone fragments in this product in comparison with their thermal stability in pure PVP.     

Reactive Compatibilization of Poly(trimethylene terephthalate)/Polypropylene Blends by Polypropylene‐graft‐Maleic Anhydride. Part 1. Rheology,Morphology, Melting,and Mechanical Properties

Poly(trimethylene terephthalate)/polypropylene (PTT/PP) blends were prepared by melt blending. The rheology, morphology, melting, and mechanical properties of PTT/PP blends were investigated with and without the addition of polypropylene‐graft‐maleic anhydride (PP‐g‐MAH). The melt viscosity results showed that the fluid behavior of PTT/PP blends exhibited great disparity to that of PTT but similar to that of PP; the dispersed flexible PP phase in the blends served as a “ball bearing effect” under shear stress, which made the fluid resistance markedly reduced; by contrast, the relatively rigid PTT dispersed phase made only a small contribution to the viscosity. With 5 wt.% PP‐g‐MAH addition during melt processing, both the shear viscosity and the non‐Newtonian index of 70/30 PTT/PP blend were increased over that of the corresponding uncompatibilized one, whereas the shear viscosity of the 30/70 PTT/PP melt decreased slightly indicating that a considerable amount of PP‐g‐MAH did not act as compatibilizer but probably served as plasticizer.

With the increasing of the other component, the melting temperature of the PTT phase showed a slight decrease while the melting temperature of the PP phase showed a slight increase. 5 wt.% PP‐g‐MAH addition had little influence on the melting temperatures of the two components. When PP≤20 wt.%, the cold crystallization temperature of the PTT phase (T_cc (PTT‐phase)) showed little change with the composition; however, it shifted to higher temperature when PP≥30 wt.%. The variations of the T_cc (PTT‐phase), with and without PP‐g‐MAH, suggested that, when PTT was a minor component, the excess PP‐g‐MAH which did not act as compatibilizer might serve as a plasticizer that made the PTT's cold crystallization process to be easier. The SEM results indicated that, for the uncompatibilized blends, the interfaces from particles pulling‐out are clear and smooth, while, for compatibilized blends, the reactive products are at the interfaces. The mechanical properties suggested that PP‐g‐MAH did not result in significant improvement of the toughness of the blend, but the tensile strength increased markedly.     

Reactive Compatibilization of Poly(trimethylene terephthalate)/Polypropylene Blends by Polypropylene‐graft‐Maleic Anhydride. Part 2. Crystallization Behavior

The crystallization behavior of uncompatibilized and reactive compatibilized poly(trimethylene terephthalate)/polypropylene (PTT/PP) blends was investigated. In both blends, PTT and PP crystallization rates were accelerated by the presence of each other, especially at low concentrations. When PP content in the uncompatibilized blends was increased to 50–60 wt%, PTT showed fractionated crystallization; a small PTT crystallization exotherm appeared at ～135°C besides the normal ～175°C exotherm. Above 70 wt% PP, PTT crystallization exotherms disappeared. In contrast, PP in the blends showed crystallization exotherms at 113–121°C for all compositions. When a maleic anhydride‐grafted PP (PP‐g‐MAH) was added as a reactive compatibilizer, the crystallization temperatures (T _c ) of PTT and PP shifted significantly to lower temperatures. The shift of PTT's T _c was larger than that of the PP, suggesting that addition of the PP‐g‐MAH had a larger effect on PTT's crystallization than on PP due to reaction between maleic anhydride and PTT.

The nonisothermal crystallization kinetics was analyzed by a modified Avrami equation. The results confirmed that PTT's and PP's crystallization was accelerated by the presence of each other and the effect varied with blend compositions. When the PP content increased from 0 to 60 wt%, PTT's Avrami exponent n decreased from 4.35 to 3.01; nucleation changed from a thermal to an athermal mode with three‐dimensional growths. In contrast, when the PTT content increased from 0 to 90 wt% in the blends, changes in PP's n values indicated that nucleation changed from a thermal (0–50 wt% PTT) to athermal (60–70 wt% PTT) mode, and then back to a thermal (80–90 wt% PTT) mode. When PP‐g‐MAH was added as a compatibilizer, the crystallization process shifted considerably to lower temperatures and it took a longer crystallization time to reach a given crystallinity compared to the uncompatibilized blends.     

Improved piezoelectric properties of cellular polypropylene ferroelectrets by chemical modification

To improve the thermal stability of piezoelectricity of polypropylene (PP) ferroelectrets, chemical modification of the cellular PP film was performed via chromic acid oxidation and then hydrofluoric acid treatment. Deep chemical modification is achieved as indicated by the energy-dispersive X-ray analyses on the cross-section of the modified cellular PP film. The results of the isothermal decay for piezoelectric d ₃₃-coefficient at 70°C indicate the improved thermal stability of piezoelectricity and the enhanced piezoelectric activity of the modified PP ferroelectrets. The former is attributed to the improvement of thermal stability of the charges trapped in the internal void surface layers as indicated by the thermally stimulated discharge measurements, while the latter results not only from the improved thermal stability of the charges but also from the reduction in Young’s modulus of the PP ferroelectrets due to the chemical modification as revealed by the dielectric resonance analyses.     

Crystallization and Thermal Conductivity of CaCO3 Nanoparticle Filled Polypropylene

Isotactic polypropylene (IPP) and calcium carbonate (CaCO₃) nanocomposites were prepared by melt extrusion in a twinscrew extruder. The effect of CaCO₃ nanoparticles on the crystallization and thermal conductivity (TC) of PP was studied by thermal analysis (DSC) and thermal conductivity analysis (TCA). The introduction of CaCO₃ nanoparticles resulted in an increase in crystallinity. The incorporation of this nanoparticle (up to 15 phr) caused a significant increase of TC of PP, especially for larger filler content. Several models were used for prediction of TC of the nanocomposites. The experimental results had a good correlation with the Ce Wen Nan Model.     

聚丙烯/抗老化剂复合体系的γ-射线辐照降解研究

研究了聚丙烯(PP)及含有受阻酚类抗氧剂和受阻胺类光稳定剂复合体系的PP复合物经过γ-射线辐照后发生的结构变化及抗老化剂所起作用。实验利用红外光谱(FTIR)和示差扫描量热法(DSC)对PP的结构变化进行了系统表征。研究结果表明,当辐照剂量较小(50 kGy)时,纯PP及其复合物体系均未发生明显降解;当辐照剂量较大(≥50 kGy)时,PP及其复合物的羰基指数迅速提高,二者的结晶温度和熔融温度大幅度降低,说明PP发生了严重降解。在相同γ-射线辐照剂量条件下(≥50 kGy),PP复合物的羰基指数高于纯PP,而结晶温度以及熔融温度低于纯PP,表明高辐照剂量下抗老化剂复合物的存在不但没有阻止聚丙烯的降解,反而加快了降解的速率。     

Glass transition temperature and thermal stability of ZnS/PMMA nanocomposites

In this article, ZnS nanoparticles were prepared by wet chemical precipitation method using zinc sulphate (ZnSO₄), sodium sulphide (Na₂S) and thio-glycerol. These nanoparticles were characterized through X-ray diffraction (XRD) and transmission electron microscope (TEM) measurements. The solution-based processing was used to prepare Poly methyl methacrylate (PMMA) nanocomposites with different weight percents (0, 2, 4, 6 and 8) of ZnS nanoparticles. The obtained ZnS/PMMA nanocomposites were characterized through XRD, scanning electron microscope and TEM measurements. The dynamic mechanical analyzer was used to obtain the storage modulus and glass transition temperature (T _g) of the nanocomposites. The apparent activation energy of the glass transition region was also determined using the Vogel–Fulcher–Tammann equation. The results indicated that the thermal stability of ZnS/PMMA nanocomposites was higher than PMMA and 6 wt. % of ZnS nanoparticles in PMMA matrix showed the maximum activation energy, which indicated that this nanocomposite had higher thermal stability than other composites.     

Thermal and Structural Behaviors of Polypropylene Nanocomposites Reinforced with Single-Walled Carbon Nanotubes by Melt Processing Method

In this work, polypropylene (PP) matrix reinforced with several single-walled carbon nanotubes (SWNTs) concentrations were prepared by a melt-mixing method. The effect of SWNTs on the thermal degradation behavior of polypropylene was studied by thermal gravimetric analysis. The results revealed that adding the SWNTs into the PP can increase the decomposition temperature. The results obtained from differential scanning calorimetry showed that incorporating SWNTs reduced the crystallinity but increased the crystallization temperature of the PP. The mechanical measurements showed that the tensile modulus of the nanocomposite was greatly enhanced to 882 MPa, compared to 485 MPa for pristine PP. For wide-angle X-ray diffraction tests, two cooling methods were used. The addition of SWNTs to the polymer in slow-cooled samples resulted in partial crystallization in the γ -form, while SWNTs had no effect in water-cooled samples, the sample crystallizing in the α -form. Scanning electron microscopy observations on the fracture surface of the nanocomposites showed the dispersion of the SWNTs in the nanocomposites.     

Effect of Compatibilizer Content on the Shear and Extensional Rheology of Polypropylene/Clay Nanocomposites

The shear and extensional rheology of polypropylene (PP)/organoclay nanocomposites in the presence of various maleic anhydride grafted polypropylene (PP-g-MA) compatibilizer concentrations were investigated. The PP nanocomposites were prepared via direct melt intercalation in an internal mixer. The structures of the nanocomposites were characterized by X-ray diffraction (XRD) and scanning electron microscopy. It was found that both the compatibilized and uncompatibilized nanocomposites could form an intercalated structure. However, the organoclay particles can disperse well only in the compatibilized systems. The linear viscoelastic properties, including the storage modulus G′ and complex viscosity η* were very sensitive to the microstructure of the nanocomposites. The extensional viscosities of PP nanocomposites were enhanced under a low deformation rate with increasing compatibilizer content and displayed a lack of superposition for different strain rates. It was proposed that the lack of superposition might originate from the formation of a three-dimensional organoclay network, which decreased in its complexity and strength as the deformation rate increased.