Non-isothermal crystallization of polyamide 6 matrix in all-polyamide composites: crystallization kinetic, melting behavior, and crystal morphology

The difference in the melting points of polyamide 66 (PA66) fiber and polyamide 6 (PA6) film permits the preparation of all-polyamide (all-PA) composites by film-packing. Good interface performance and integrated consolidation structure in this all-PA composite are contributed to the similar chemical composition between PA66 fiber and PA6 matrix. In this paper, the non-isothermal crystallization kinetics and melting behaviors of PA6 matrix in all-PA composite are studied by differential scanning calorimetry (DSC), in which the modified Avrami equation, Ozawa model, and Mo equation combining Avrami and Ozawa equation are employed. It is found that the Mo equation exhibits great advantages in treating the non-isothermal crystallization kinetics for both neat PA6 and PA6 matrix in all-PA composite. The crystal morphologies of single PA66 fiber–PA6 composite by polarizing microscope (POM) clearly show a transcrystallinity layer of PA6 around PA66 fiber that proves a remarkable nucleation effect of PA66 fiber surface on the crystallization of PA6 matrix.     

Preparation of Semi-aromatic polyamide(PA)/multi-wall carbon nanotube (MWCNT) composites and its dynamic mechanical properties

Well dispersed semi-aromatic polyamide(PA)/multi-wall carbon nanotube (MWCNT) composite was prepared through high-speed shearing method in the presence of surfactant sodium dodecylbenzene sulfonate (SDBS). Further analysis of morphology, crystallization, and dynamical mechanical properties shows the presence of SDBS helps to disperse the MWCNT and largely enhance the mechanical property. In comparison with neat PA component, the storage modulus (E′) of the blend system at 90 °C is 3.5 times larger than PA with MWCNT load ratio of 3 wt.%; and meanwhile the glass transition temperature (T _g) of PA component increases about 17 °C; Similar phenomena have not found in MWCNT/PA composite without surfactant. Simultaneously, as DSC and morphology measurements indicate, the filled MWCNT does not show tremendous effect on the crystalline phase and crystallinity of PA, which imply that the increasing mechanical property for composites is due to the strengthening effect of MWCNT itself, not being caused by the change of crystalline phase and crystallinity by the addition of MWCNT. The increasing T _g, indicative of the restricting movement of PA chains, is most probably ascribe to the strong interaction presented between MWCNT and PA chains.     

Manufacturing and physical properties of all-polyamide composites

Based on the difference in melting points between polyamide 66 (PA66) fiber and polyamide 6 (PA6) matrix, all-polyamide composites were fabricated under various processing conditions. In these all-polyamide composites, the reinforcement and matrix share the same molecular structure unit (–CONH–(CH₂)₅–). Because of the chemical similarity of the two components, good bonding at the fiber/matrix interface could be expected. Effects of processing temperature and cooling rate on the structure and physical properties of composites were investigated by SEM, DMA, DSC analyses, and static tensile test. Fiber/matrix interface strength benefited from elevated processing temperature. The static tensile results showed that the maximum of tensile strength was observed in the processing temperature range of 225–245 °C. At different cooling rates, crystallization temperature of PA6 in the composites was increased compared to the pure PA6 because of the nucleation effect of PA66 fiber surface to the PA6 matrix. A study of the matrix microstructure in a single fiber-polymer composite gave proof of the transcrystalline growth at the fiber–matrix interface, the reason behind which was the similar chemical compositions and lattice structures between PA6 and PA66.     

热塑性聚氨酯/尼龙612共混体系的相互作用及结晶行为

采用溶液共沉淀法制备了热塑性聚氨酯(TPU)/尼龙(PA)612共混物,通过变温红外光谱仪和差示扫描量热仪(DSC)研究了共混体系中 TPU与PA612分子间的相互作用及其对结晶行为的影响.DSC结果表明,随着共混体系中TPU含量的增加,PA612的结晶峰温度明显降低,结晶峰宽明显变宽;相对于纯TPU,共混体系中TPU...     

木粉/低熔点尼龙6复合材料的非等温结晶动力学

利用LiCl改性尼龙6 (PA6),并将其与木粉熔融共混制备了木粉/低熔点PA6复合材料,通过DSC法研究了木粉/低熔点PA6复合材料的非等温结晶动力学行为。结果表明,LiCl降低了PA6的熔点、结晶温度、结晶度和结晶速率,提高了PA6的结晶活化能。木粉是良好的成核剂,能够加快PA6的结晶速率,但却降低了其结晶度。通过Mo法分析木粉/低熔点PA6复合材料的非等温结晶动力学,结果表明,与纯PA6和木粉/PA6复合材料相比,低熔点PA6的F(T)值(表征聚合物结晶快慢参数)最大,LiCl提高了PA6在单位结晶时间内达到一定结晶度时所需的冷却速率,而木粉则与之相反。      

PA6/PA6IcoT相容共混物的结晶行为

采用差示扫描量热法研究了熔融共混聚己内酰胺/聚对(间)苯二甲酸己二胺(PA6/PA6IcoT)相容体系的结晶温度、结晶程度以及结晶动力学,并通过热台偏光显微镜、广角X射线衍射仪观察了PA6/PA6IcoT共混体系的结晶相形态和晶体结构。结果表明,共混物的结晶行为与其组成、结晶温度区域密切相关。在非等温结晶时,随着非晶态PA6IcoT含量的增加,PA6相的相对结晶度增加,部分晶体结构由γ晶型转变为较完善的α晶型。在较高温度区域结晶时,少量的PA6IcoT就能使串并的晶核分开,形成大量微小晶粒。当PA6IcoT含量继续增加时,球晶数目会减少但尺寸增大。等温结晶动力学研究发现,结晶速度随PA6IcoT含量的提高而下降,Avrami指数值在4.5～6之间,并随着结晶温度升高而增大。     

Non-isothermal Crystallization Kinetics of Polyamide 6/Diamine-modified MWNTs Nanocomposite

The non-isothermal crystallization kinetics of polyamide 6/diamine-modified multi-walled carbon nanotube (PA6/D-MWNT) nanocomposite was investigated by differential scanning calorimetry (DSC). The modified Avrami equation, the Ozawa equation and the combined Avrami/Ozawa equation were employed to analyze the non-isothermal crystallization data. The crystallization activation energies were also evaluated by the Kissinger method. It was found that the combined Avrami/Ozawa equation could successfully describe the non-isothermal crystallization process. The results showed that D-MWNTs not only acted as effective heterogeneous nucleating agents for PA6 and noticeably increased the crystallization temperature of PA6, but also influenced the mechanism of nucleation and crystal growth of PA6 and then reduced the overall crystallization rate of the neat PA6 matrix. The crystallization activation energy for the nanocomposite sample was greater than that of the neat PA6, which indicated that the addition of D-MWNTs hindered the mobility of PA6 chain segments.     

Polymorphism and Crystal Growth of Phenylbutazone in Semisolid Preparations. Part One: Characterisation of Isolated Crystals from Commercial Creams of Phenylbutazone

It has been observed that a commercial product of phenylbutazone cream (o/w type) shows gritty appearance. Large Crystals up to 1000 μm in diameter have been isolated from unexpired batches. New batches from the same product show crystal size up to 150 μm in diameter. Investigation of the physical characters of the isolated crystals have been done in comparison with a pure phenylbutazone sample (99.5%). UV-Spectrophotometric analysis of the isolated crystals indicates phenylbutazone content of 90%. However, TLC examination and UV, IR and NMR Spectra examinations indicate the absence of decomposition products. Oily material has been separated from the isolated crystals by phosphate buffer solution (pH. 6.90).

DSC examinations of the isolated crystals show two endothermic peaks at 76°C and 100.1°C and one exothermic peak at 81°C. The endothermic peak at 76°C is interpreted as a result of the interaction between phenylbutazone and the oily material.

The examination of the isolated crystals before and after isothermal transformation and during melting by both hot stage microscope, ESM, (IR) and DSC indicates that the presence of phenylbutazone in the crystals is not a mechanical entrapment. It suggests that phenylbutazone interacts with the fatty base on the molecular level and both crystallise out from the cream.     

Combining thermodynamics and DSC to characterize the melting and wetting behavior of a composite powder used for joining ceramics

The diffusion-assisted melting behavior of a Cu-coated Ti-powder was characterized as a function of the intermetallic formation and corresponding melting temperature using DSC. The endothermic and exothermic events were identified using the respective binary phase diagram. The results demonstrated that initial melting is independent of the heating rate; however complete melting occurred at 900°C when heated at 10°C/min as oppose to 915°C for a heating rate of 40°C/min. The wetting results of the brazing alloy on Si₃N₄ ceramic show that the brazing alloy maintains its initial shape until the complete melting is achieved. Equilibrium contact angle measurements obtained are similar to results previously published but the wetting kinetics observed are different.     

Morphology,thermal and mechanical behavior of polyamide 6/layered-silicate nanocomposites

The microstructure, morphology, thermal and mechanical properties of polyamide 6/layered-silicate nanocomposites (PLSN) have been studied using X-ray diffraction (XRD), tapping-mode atomic force microscopy (AFM), differential scanning calorimetry (DSC) and tensile tests. The XRD and AFM results indicate that the organically-modified layered silicates are intercalated in the polyamide 6 (PA6) matrix. Also, the crystallization and thermal behavior of PA6 are influenced by the addition of layered silicates into polymer matrix. A silicate-induced crystal transformation from the α-form to the γ-form of PA6 is confirmed by XRD and DSC, i.e., the formation of γ crystal is enhanced by the presence of silicates. In comparison to PA6, the thermal property of PLSN has been investigated using DSC. The possible origins of a new silicate-induced endothermic peak are discussed. Tensile tests show that the tensile modulus and yield strength increase while the strain-at-yield decreases with increasing clay loading.     

聚苯硫醚/尼龙6共混物的结晶与熔融行为

用ＤＳＣ研究了不同组成比的聚苯硫醚（ＰＰＳ）／尼龙６（ＰＡ６）共混物中ＰＰＳ和ＰＡ６组分的结晶与熔融行为及其相互作用的影响,结果表明,ＰＰＳ在ＰＡ６熔体存在下结晶温度明显提高,结晶峰形变窄;随ＰＡ６含量增加,ＰＰＳ的结晶温度移向高温,甚至ＰＰＳ成为分散相,这一作用还十分明显;而ＰＰＳ的熔融温度受共混影响较小,结晶了的ＰＰＳ也使ＰＡ６的结晶温度有所提高,但不如ＰＰＳ的结晶温度提高明显;当ＰＡ６为分散     

线型与星型聚酰胺6-聚氨酯嵌段共聚物的性能比较

以聚醚多元醇(PPG)、二苯甲烷二异氰酸酯(MDI)以及己内酰胺为单体,在碱性催化剂条件下,通过单体浇铸(MC)工艺制备了线型和星型聚酰胺6/聚氨酯(PA 6-PU)嵌段共聚物。使用差热分析(DSC),扫描电镜分析(SEM)研究了两者的结晶和熔融行为以及微观结构,并进行了比较。研究发现,与线型PA 6-PU嵌段共聚物相比,随着PU组分含量的增加,星型PA 6-PU嵌段共聚物具有较高的熔融温度(Tm)和结晶温度(Tc),并且,两共聚物中的PU与PA的相容性好。比较两者的力学性能,结果显示,同等PU添加量时,星型PA 6-PU嵌段共聚物冲击性能的提高更为明显。     

PA6/POE/OMMT纳米复合材料的非等温结晶行为

采用差示扫描量热仪(DSC)研究了熔融插层法制备的尼龙6/乙烯-辛烯共聚物/有机改性蒙脱土(PA6/POE/OMMT)纳米复合材料的结晶行为,用Jeziorny法和Mo法分析了复合材料的非等温结晶动力学,并计算得到了相关的结晶动力学参数.结果表明,纳米粘土对基体有异相成核作用,但随着其在复合材料中含量增加,半结晶时间t...     

Miscibility and melting properties of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate) blends

The miscibility and melting properties of binary crystalline blends of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate) (PEN/PTT) have been investigated with differential scanning calorimetry (DSC). The glass transition and cold crystallization behaviors indicated that in PEN/PTT blends, there are two different amorphous phases and the PEN/PTT blends are immiscible in the amorphous state. The polymer–polymer interaction parameter, , calculated from equilibrium melting temperature depression of the PEN component was −1.791 × 10⁻⁵ (300 °C), revealing miscibility of PEN/PTT blends in the melt state.     

Phase transformation of calcia-alumina-magnesia fibres produced by inviscid melt spinning

CaO-Al₂O₃-MgO (CAM) ceramic fibre produced via inviscid melt spinning (IMS) was investigated for phase transformation. Differential thermal analysis (DTA) on the as-spun CAM fibre gave two transformation peaks, one for exothermic peak at around 927°C and the other for endothermic one at around 1100°C. In order to identify each phase transformation x-ray diffraction (XRD) analysis was performed on the CAM fibres heat-treated to each phase transformation completion temperature. The exothermic peak was determined to represent crystallization of remaining amorphous phase in the as-spun CAM fibre. The endothermic peak was determined to correspond to transformation of non-equilibrium CaO · Al₂O₃ phase to equilibrium 3CaO· 5Al₂O₃ phase.     

Recycling of waste nylon 6/spandex blended fabrics by melt processing

A unique approach for reclaiming waste nylon 6/spandex blended fabrics was demonstrated by melt processing through mixing and molding. Spandex from the waste fabrics was removed by hydrolysis under controlled conditions. Morphological analysis showed that the fracture surface was homogeneous for samples of neat nylon 6 and treated fabrics, and voids were observed for samples from untreated fabrics. Thermal analysis indicated that the materials from waste fabrics exhibited both similar melting temperature (around 220 °C) and similar crystallization temperature (around 185 °C). Infrared spectroscopy showed nearly the same main absorption peaks of neat nylon 6 and samples from nylon 6/spandex fabrics. The viscosity of treated fabric samples was lower than that of untreated fabric composites at low and medium frequencies, as an effect of the spandex removal after treatment. The recycled plastics from treated fabrics exhibited good mechanical properties with a tensile strength of 46.6 MPa and a Young's modulus exceeding 2.4 GPa.     

热致液晶聚酰胺与尼龙66相容原位复合材料研究

合成了半柔性热致液晶聚酰胺(TLCPa),通过熔融共混方法制备了TLCPa/PA66共混物.用差示扫描量热(DSC)、广角X射线衍射(WAXD)、扫描电子显微镜(SEM)和傅里叶红外光谱(FTIR)等分析手段对共混物进行了综合研究.DSC研究表明:TLCPa的加入使共混物的熔融温度和结晶温度向低温方向漂移,结晶速率下降.根据WAXD分析:强剪切有利于TLCPa与PA66分子间形成氢键作用,TLCPa与PA66形成共晶.SEM分析显示:TLCPa与PA66具有良好的相容性,沿流动方向TLCPa变形成为微纤.FTIR分析显示TLCPa与PA66分子间存在氢键作用.     

The hot compaction of SPECTRA gel-spun polyethylene fibre

The compaction of gel-spun high molecular weight polyethylene (PE) fibre, SPECTRA 1000, has been investigated for a range of compaction temperatures between 142 °–155 °C. Differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and broad-line nuclear magnetic resonance (NMR) techniques have been used to examine the structure of the compacted materials and to determine the compaction mechanisms. With increasing compaction temperature, the flexural properties of the compacted materials did not show any significant change up to 154 °C, but large changes were observed if the temperature was increased from 154 to 155 °C. DSC and SEM studies revealed that no evident surface melting and recrystallization occurred during hot compaction in the temperature range 144–154 °C, although the rigid crystalline fraction measured by NMR for all compacted materials is significantly lower than that for the original fibre. Significant transverse strength is also developed at the lower compaction temperatures, and this also only markedly increases on going from 154 to 155 °C. Structural investigations show how the fibres deform so as to interlock, and localized welding occurs, so as to bond each fibre to its neighbour. This is distinct from the melting and recrystallization at the surface of the fibres previously observed in melt spun fibres. This revised version was published online in November 2006 with corrections to the Cover Date.     

PA6/PTT共混物的吸水性和力学性能

由螺杆挤出机制备了尼龙6(PA6)和聚对苯二甲酸丙二醇酯(PTT)的共混物PA6/PTT。通过浸水实验,结合扫描电镜观察和热分析,研究了不同组分PA6/PTT共混物的吸水性能,并进行了相关力学性能测试。结果表明,PA6/PTT共混物吸水率随PTT含量增加而减小,即PTT的加入有效抑制了PA6的吸水率;在相同吸水条件下,PA6/PTT共混物的一般力学性能明显优于PA6,当PTT含量为20%时,共混物吸水后的拉伸、弯曲强度分别较PA6提高了20.98%和71.73%。     

Low temperature exothermic effects on cooling of homoionic clays

Results of differential scanning calorimetry (DSC) experiments on homoionic montmorillonites (Ca²⁺, Mg²⁺, Na⁺, K⁺) and Na-kaolinite are reported. The low temperature exothermic peaks were observed on cooling down to − 90 °C after the initial peak corresponding to the breakdown of supercooling of water in macro- and mezopores. In some experiments, the samples were then warmed to − 10 °C or − 5 °C and cooled again to − 90 °C. According to expectations, the non-equilibrium exothermic peaks were absent in this case, being replaced by a wide peak analogical to that obtained on warming. However, the low temperature exothermic peaks were still observed, but their fields were characteristically cut, proportionally to the extent of the previous warming. The stochastic deconvolution applied to the endothermic peaks obtained on warming allowed to compare the thermal effects corresponding to the cooling and warming. The results gave evidence that the portion of water, solidification of which can be attributed to the low temperature exothermic peaks, on warming melts in a wide temperature range and a separated melting point does not exist.