Crystallization of filled Nylon 6 II. Isothermal crystallization

Summary Isothermal crystallization kinetics from the melt of nylon 6 containing various amounts of untreated glass beads and Aerosil (series GB and A) and aminosilane-treated glass beads (series GBA) was studied by DSC method. Treatment of experimental data in terms of Kolmogorov-Avrami equation has shown that time exponentn is relatively insensitive to presence of GBA filler, whereas it was found to decrease gradually with increasing filler content in samples of GB and A series to value as low as 0.5 for sample A–67. Nucleation free energy was the same in pure nylon 6 and filled samples of GBA series, but dropped suddenly in samples of GB series when mean interparticle separation x decreased below critical value _crit =(5–10) x 10^–6 m. Taking into account the concomitant drop of equilibrium melting temperature, it was concluded that these effects are a consequence of specific structural change in polymer phase accompanying transition into a boundary state. Temperature dependence of polyer crystallization rate in highly filled samples of A series at small supercoolings was found to obey them=4 law, which is characteristic of transformations in strained media. Experimental data seem to be consistent with the idea that the postulated strain energy might originate from negative capillary pressure between high-surface energy solid particles wette d by polymer melt. Quantitative analysis of overall crystallization rate dependence on interparticle distance x has shown that _crit may be identified with change of growth morphology from a three-dimensional to a two-dimensional one, while slowing down of growth rate at lower values of was attributed to increase of nucleation free energy due to increasing contribution from capillary forces.With 13 figures and 2 tables     

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     

Investigation on nonisothermal crystallization kinetics of the high‐flow nylon 6 by differential scanning calorimetry

The crystallization kinetics of the high‐flow nylon 6 containing polyamidoamine (PAMAM) dendrimers units in nylon 6 matrix was investigated by differential scanning calorimetry. The Ozawa and Mo equations were used to describe the crystallization kinetics under nonisothermal condition. The values of Avrami exponent m and the cooling crystallization function F(T) were determined from the Ozawa plots, which showed bad linearity, and were divided into three sections depending on different cooling rates. The plots of the m and log F(T) values versus crystallization temperatures were obtained, which indicated that the actual crystallization mechanisms might change with the crystallization temperatures. The high‐flow nylon 6 has higher values of m and log F(T) than those of pure nylon 6, which implied that the high‐flow nylon 6 had more complicated crystallization mechanisms and slower crystallization rate than those of pure nylon 6. The good linearity of the Mo plots verified the success of this combined approach. The activation energies of the high‐flow nylon 6 ranged from 157 to 174 kJ/mol, which were determined by the Kissinger method. The ΔE values were lower than those of pure nylon 6, and the ΔE values were affected by both the generation and the content of PAMAM units in the nylon 6 matrix. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2201–2211, 2008     

Fabrication of thermoplastic composites using fly-ash a coal and hollow glass beads to study their mechanical,thermal, rheological,morphological and flame retradency properties

Thermoplastic polycarbonate (PC) and nylon 6 (NY) composites with cenosphere and hollow glass beads were prepared and their mechanical, rheological, thermal and flame retardency properties were studied. The flexural behavior of the composites increased after loading with cenosphere and hollow glass beads. The tensile strength of the PC composites was enhanced up to 80 N mm^–2 as compared to pure PC while no remarkable change was observed in case of nylon 6 composites. Study of thermogravimetric Analysis (TGA) showed that the thermal stability of all the composites (Polycarbonate/cenosphere, Polycarbonate/hollow glass beads, Nylon 6/cenosphere and Nylon 6/hollow glass beads) increased. It was concluded that both the fillers enhanced the non-flammability of the polymers. Limiting oxygen index (LOI) value of all the composites showed an increase with increase in the concentration of filler. The optimal results of LOI and UL 94 were observed in composites with 8% cenosphere and 12 % cenosphere in case of Nylon 6. Cenosphere led to superior mechanical properties of polycarbonate and nylon 6 in comparison to hollow glass beads which suggested the composites can find use in automotive, industrial, pump component and for manufacturing of light weight parts in aeronautic industry at lower economic value.     

Structure-property relationships of copolyamides. I. Thermal properties and crystallization

Six nylon salts [hexamethylenediammonium adipate (6.6), hexamethylenediammonium terephthalate (6.T), hexamethylenediammonium isophthalate (6.I), p-xylylenediammonium adipate (PXD.6), m-xylylenediammonium adipate (MXD.6), and m-xylylenediammonium isophthalate (MXD.I)] were copolymerized with ε-caprolactam. The resulting random copolyamides showed different modes of crystallization as confirmed by the melting temperature depression and the decrease in the isothermal crystallization rate. By selective hydrolysis it was found that the differences in T_m depression and isothermal crystallization rate were due to partial inclusion of comonomers in the crystal lattice. The effect of comonomer structure on the crystallization rate is also discussed.     

Interfacial effects on the ageing behavior of high density polyethylene filled with glass spheres

The stress relaxation and creep behavior of unfilled high density polyethylene (HDPE) and HDPE filled with untreated and surface-treated glass spheres were measured at room temperature. A silane-based coupling agent capable of providing a covalent bond between HDPE and the glass spheres was used for the surface-treatment. Two different amounts of the coupling agent were employed giving silane layers on the fillers with different thicknesses. The effect of ageing time at room temperature on the viscoelastic properties after quenching from 100 °C to room temperature in ice water was also investigated. The effects of the surface treatment of the fillers and the ageing time was characterized by means of the internal stress ( _i ) concept. The _i -value increased with the degree of interaction of the filler/matrix interface and the ageing time. It was here not possible to superimpose the different flow curves with regard to the ageing time with sufficient accuracy. This is due to the variation of _i with ageing time. The surface-treatment of the filler had a marked effect on the creep behavior at high applied stress levels and on the ageing behavior of the composites, presumably due to the formation of an interphase region close to the filler surface with different properties and different ageing characteristics than that of the bulk of the matrix.     

Effect of Surface Treatment of Titanium Dioxide Nanoparticles on Non-Isothermal Crystallization Behavior,Viscoelastic Transitions and Cold Crystallization of Poly(Ethylene Terephthalate) Nanocomposites

The effect of untreated and tri-n-octylphosphine oxide (TOPO) surface-treated TiO₂ nanoparticles when included as filler in poly(ethylene terephthalate) on its compatibility, non-isothermal crystallization behavior, viscoelastic transitions and cold crystallization has been studied. The effectiveness of the surface treatment has been studied using infrared spectrophotometry (FTIR) and thermogravimetric analysis (TGA). The effect of the untreated and surface-treated nanofiller content in the polymer, added by an extrusion process, on the non-isothermal crystallization has been studied by differential scanning calorimetry (DSC). The influence on the viscoelastic transitions and cold crystallization of PET nanocomposites has been studied through thermomechanical analysis (TMA). The surface treatment and the concentration of nanofiller influence the non-isothermal crystallization behavior, the viscoelastic transitions and the cold crystallization of the PET nanocomposites, enables us to evaluate the compatibility and the level of dispersion/aggregation of the nanofiller in the poly(ethylene terephthalate).     

The effects of glass beads and silane treatments on the curing behavior of a brominated epoxy resin: DSC analyses

The curing characteristics of a brominated epoxy resin/dicyandiamide (DICY) system filled with silane-treated glass beads are studied using isothermal differential scanning calorimetry (DSC). Three different silane coupling agents, N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane, N-[2-(vinylbenzylamino)-ethyl]-3-aminopropyl-trimethoxysilane, and 3-glycidoxypropyl-trimethoxysilane, are applied. It is found that the reaction heats of the epoxy system are little affected by the curing temperature and the untreated glass fillers, but changed with the addition of silane-coated glass beads. The effect of glass beads on the curing reaction is more significant at the low curing temperature and conversion. The silane treatment results in changes in T_g, activation energy, reaction heat, reaction rate, and reaction order. Three silanes respond differently because of their differences in the activated reaction with the matrix system. Regardless of the various curing mechanisms involved, a simple kinetic expression can describe the curing extent at 170 and 180°C with a good accuracy for all systems studied. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2063–2071, 1997     

尼龙66/蒙脱土复合材料结晶行为的研究

在密炼机中采用熔融共混法制备蒙脱土重量分数为 2 5 %、4 5 %的尼龙 6 6 /蒙脱土复合材料 .通过DSC法对非等温结晶行为及在 2 2 8～ 2 4 0℃范围内的等温结晶行为进行研究 ,并与纯尼龙 6 6进行比较 .从其等温和非等温结晶行为的研究表明 ,蒙脱土起成核剂的作用 ,它的填入使尼龙 6 6结晶速率提高 ,但填料与基体间的相互作用使其链段运动困难 ,结晶活化能提高 ;在研究的填料含量变化范围内 ,结晶行为变化不大 ,并且找到该复合材料在 2 2 8～ 2 34℃范围结晶对温度的不敏感区 ;对非等温结晶过程分析 ,刘结平 莫志深方程是适用的 ,而Ozawa方程则是不适用的 .     

Evidence for interphasial amide formation between surface-bound poly(3-aminopropyltrisiloxane) and polyamide-6 in glass bead reinforced polyamide-6 model composites

Glass beads pretreated with equal amounts of either natural abundance-or selectively ¹³C-enriched (3-¹³C)-3-aminopropyltriethoxysilane were used as filler for the preparation of polyamide-6 model composites. After isolation of the glass beads from the composite by dissolving the polymer matrix in trifluoroethanol, the glass beads were investigated by pyrolysis capillary gas chromatography–mass spectrometry. The identification of the aldimine derivatives 1 and 2 , respectively, containing the ¹³C-label at C3 next to the imine nitrogen atom provides compelling evidence for amide formation between carboxylic end-groups of the polyamide-6 and amine groups of the surface-bound poly(3-aminopropyltrisiloxane) in the interphase region during composite preparation.     

Isothermal and nonisothermal crystallization kinetics of irradiated nylon 1212

The crystallization behavior of nylon 1212, irradiated at ⁶⁰Co γ‐rays (50 kGy), was studied by a rheometer, polarized optical microscopy (POM), and differential scanning calorimeter (DSC). The results showed that irradiated nylon 1212 samples exhibited abnormal crystallization behavior during the crystallization process: The Avrami exponent n was calculated and was found to be in the range from 2.06–2.41 for isothermal crystallization, and from 2.67–4.91 for nonisothermal crystallization; the spherulite morphology also changed largely by polarized optical microscopy (POM); the crystallization activation energy ΔE for isothermal and nonisothermal crystallization process of irradiated nylon 1212 are determined to be 57.4 kJ/mol and 78.65 kJ/mol, respectively, which are lower than that of nonirradiated nylon 1212. At the same time, a new method by a combination of the Avrami and Ozawa equations was successfully applied to analyze the noncrystallization process of irradiated nylon 1212. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2326–2333, 2005     

尼龙1218的等温及非等温结晶动力学研究

采用示差扫描量热计DSC考察了一种新型长烷基链偶偶尼龙 尼龙 12 18 自熔体的结晶过程 ,分别利用Avrami方程和Ozawa方程对等温及非等温结晶动力学进行了描述与研究 ,计算了相关的结晶动力学参数 ,得出相应的结晶机理 .最后计算了等温结晶活化能和非等温结晶活化能 ,依此得到烷基链段长度与尼龙结晶过程有密切关系     

Non-isothermal crystallization of UHMWPE filled during polymerization with inorganic fillers

The non-isothermal crystallization of UHMWPE, filled with different inorganic fillers during the polymerization on the catalyst system TiCl₄/(C₂H₅)₂AlCl/(C₆H₅)₂Mg has been studied by DSC and polarization microscopy. The melting conditions of UHMWPE have been established before the crystallization experiments. It is shown that the fillers act as nucleating agents only when the crystallization is carried out from a melt, obtained at temperature above the flow temperature of UHMWPE, and at slow cooling rate. It was established that the efficiency of nucleation passes through maximum at 50 wt.% of the filler. It is assumed that this is due to the reduction of the heterogeneous sites, because of the aggregation of the filler with high concentration. The non-isothermal crystallization kinetics is studied by Harnisch and Muschik method. The Avrami exponents do not change in the presence of a filler with concentration up to 90 wt.%.     

Flash DSC crystallization study of blown film grade bimodal high density polyethylene (HDPE) resins. Part 2. Non‐isothermal kinetics

Non‐isothermal ultra‐fast cooling crystallization tests were conducted on three blown film grade bimodal high density polyethylene (HDPE) resins using a fast differential scanning calorimeter, the Flash DSC. Non‐isothermal tests were performed at cooling rates between 50 and 4000°K/s, and the data were analyzed using the modified Avrami model by Jeziorny (Polymer, 1978 , 19, 1142). Non‐isothermal data were used to propose a new method named crystallization–time–temperature–superposition, and the two activation energies were obtained for each of the resins. This is very useful for obtaining theoretical crystallization kinetics data at different cooling rates, allowing its use in ultra‐fast cooling polymer processes such as blown film. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1822–1827     

New insights into the cold crystallization of filled natural rubber

This article is devoted to the cold crystallization of filled natural rubber with different types of filler such as carbon black, silica, and grafted silica. A large set of differential scanning calorimetry data is presented with various scanning rates, times, and temperatures of isothermal crystallization to display the factors affecting natural rubber (NR) crystallization. The crystallization kinetic measurements suggest that fillers can create a region with perturbed mobility where the kinetics of nucleation and/or growth are slowed down, the rest of the matrix being unperturbed. And, the final crystallization level indicates the existence of an excluded region for crystallization close to the filler surface. Furthermore, the presence of fillers appears less unfavorable to NR crystallization than chemical crosslinking. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 955–962, 2007     

Effect of fly ash silica and precipitated silica fillers on the viscosity,cure, and viscoelastic properties of natural rubber

The viscosity, cure properties, storage, and loss moduli and tan δ of natural rubber (NR) filled with the same amounts of precipitated silica (PSi) and fly ash silica (FASi) fillers were measured. The fillers were treated with bis[3‐triethoxysilylpropyl‐]tetrasulfide (TESPT), or, used in the rubber untreated. TESPT is a sulfur‐containing bi‐functional organosilane that chemically adheres silica to rubber and also prevents silica from interfering with the reaction mechanism of sulfur cure. The dispersion of PSi and FASi in the rubber was investigated using scanning electron microscope (SEM). The effects of silica type and loading and surface treatment on the aforementioned properties were of interest. The SEM results showed that the FASi particles were larger in size and had a wider particle size distribution when compared with the PSi particles. The viscosity of the compounds decreased progressively with mixing time, and the compounds with FASi had a lower viscosity than those filled with PSi. The treatment with Si69 had no beneficial effect on the dispersion of the fillers in the rubber matrix. At low temperatures, the type and loading of the filler had no effect on the storage and loss moduli of the compounds, but the effect was more pronounced at high temperatures. There was also evidence from the tan δ and glass transition temperature (T_g) measurements that some limited interaction between the filler particles and rubber had occurred because of TESPT. Copyright © 2008 John Wiley & Sons, Ltd.     

Polymorphism of nylon‐6 in multiwalled carbon nanotubes/nylon‐6 composites

The effects of pristine and amino‐functionalized multiwalled carbon nanotubes (MWNTs) on the crystallization behaviors of nylon‐6 were investigated by differential scanning calorimetry and X‐ray diffraction. The results indicate the presence of polymorphism in nylon‐6 and its composites, which is dependent on the MWNTs concentration and the cooling rate. More MWNTs and slow cooling from the melt favors the formation of α crystalline form. With the increase in cooling rates, the crystallinity of neat nylon‐6 decreases, and that of the composites decreases initially but increases afterward. Moreover, the degree of crystallinity of the composites is higher than neat nylon‐6 under high cooling rates, counter to what is observed under low cooling rates. The heterogeneous nucleation induced by MWNTs and the restricted mobility of polymer chains are considered as the main factors. Furthermore, addition of MWNTs increases the crystallization rate of α crystalline form but amino‐functionalization of MWNTs weakens this effect. The influence of thermal treatment on the crystalline structure of MWNTs/nylon‐6 composites is also discussed. A γ–α phase transition takes place at lower temperature for MWNTs/nylon‐6 composites than for nylon‐6. The annealing peaks of the composites annealed at 160 °C are higher than that of neat nylon‐6, and the highest annealing peak is obtained for amino‐functionalized MWNTs/nylon‐6 composites. This phenomenon is closely related to the different nucleation and recrystallization behaviors produced by various MWNTs in confined space. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1499–1512, 2006     

Crystallization of poly(ethylene terephthalate) induced by inorganic compounds. I. Crystallization behavior from the glassy state in a low-temperature region

The kinetics of isothermal crystallization from the glassy state at low temperatures and the morphology of poly(ethylene terephthalate) (PET) filled with additives are reported. Talc, kaolin, silicon oxide, and titanium oxide have been used as fillers; they act as effective nucleating agents for PET. The overall rate of crystallization depends on the volume concentration, the size distribution, and the nucleating ability of the additives. An electron microscopic study reveals a transcrystalline morphology at the surface of the filler particles. The occurrence of transcrystallinity is attributed to extensive heterogeneous nucleation induced at the filler surface. From the shape of the crystallization isotherms, it can be concluded that the crystallization mechanism depends on the type of filler.     

Thermal analysis of the double-melting behavior of poly(L-lactic acid)

The melting and crystallization behavior of poly(L -lactic acid) (PLLA; weight-average molecular weight = 3 × 10⁵) was studied with differential scanning calorimetry (DSC). DSC curves for PLLA samples were obtained at various cooling rates (CRs) from the melt (210 °C). The peak crystallization temperature and the exothermic heat of crystallization determined from the DSC curve decreased almost linearly with increasing log(CR). DSC melting curves for the melt-crystallized samples were obtained at various heating rates (HRs). The double-melting behavior was confirmed by the double endothermic peaks, a high-temperature peak (H) and a low-temperature peak (L), that appeared in the DSC curves at slow HRs for the samples prepared with a slow CR. Peak L increased with increasing HR, whereas peak H decreased. The peak melting temperatures of L and H [T_m(L) and T_m(H)] decreased linearly with log(HR). The appearance region of the double-melting peaks (L and H) was illustrated in a CR–HR map. Peak L decreased with increasing CR, whereas peak H increased. T_m(L) and T_m(H) decreased almost linearly with log(CR). The characteristics of the crystallization and double-melting behavior were explained by the slow rates of crystallization and recrystallization, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 25–32, 2004