Study on the non-isothermal crystallization behaviors of PA6/silica nanocomposites prepared by the sol–gel process

A organic–inorganic PA6/partially functionalized silica hybrid nanocomposites was prepared by caprolactam polymerized and silica nanoparticles in situ gernerated through condensation of partially functionalized silicic acid, which was prepared through hydrolysis of tetraethoxysilane (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTES), in one process. The non-isothermal crystallization behaviors of pure PA6, PA6/unfunctionalized silica (PA6S) and PA6/functionalized silica (PA6FS) hybrid materials were investigated by differential scanning calorimetry (DSC). Two methods, namely, the Avrami and the Mo, were applied to describe the crystallization process of these three materials. DSC results showed that the crystallization rates of PA6FS is faster than that of pure PA6 and PA6S at the same cooling rate, the nano-silica particles functionalized by GPS in hybrid material acted as more effective nucleation agents, and the crystallization rates of all these samples increased with the cooling rate increasing. XRD results indicated that the addition of functionalized nano-silica particles favored the formation of the γ crystalline form.     

An unusual morphology and crystallization behavior in in situ formed polyphenylene oxide/polyamide 6 blends

Novel polyphenylene oxide/polyamide 6 (PPO/PA6) blends were synthesized via in situ polymerization of ε-caprolactam with PPO dissolved in it. The introduction of 10 wt% PPO into PPO/PA6 led to phase inversion of the blends, which was nearly completed by incorporating 15 wt% PPO into the blends. A single crystallization temperature (T _c) of PA6 was detected for PPO/PA6 with 1–4 wt% PPO, while double T _c existed in the blends with 6–15 wt% PPO. After eliminating previous thermal history, PPO/PA6 containing no more than 6 wt% PPO gave a single melting point (T _m), but the blends with 10–15 wt% PPO exhibited double T _m. Increasing PPO content in PA6 resulted in the transformation of its crystal form from α-crystal to γ-crystal, which might be attributed to hindrance of crystallization of PA6 particles in PPO-rich phase.     

PA-6/ABS共混体系中加入SMA的反应型增容作用

加入少量苯乙烯－马来酸酐共聚物,能改善苯不相容的尼龙－６／ＡＢＳ共浊 系的相容性,提高其力学性能。文中共混物的熔体流变性能,ＤＳＣ表征及相结构观察,表明相容性的改善是在熔融共混过程中ＳＭＡ在ＰＡ－６和ＡＢＳ界面的的接枝反应得以实现。     

Microstructural,thermal and rheological correlations to mechanical response of polyamide-6(glass filled)/polyetherimide blend: effect of ethylene-octene copolymer on toughening of blend

Melt mixed glass-filled polyamide 6(PA6)/polyetherimide (PEI) blends were prepared in a co-rotating twin screw extruder over the entire composition range of 0–100 wt% of polyamide 6. These blends were characterized by structural, rheological, mechanical and thermal properties. Crystallization behavior and phase morphology of the blends were also investigated. The blend with the composition PA6/PEI 75/25 showed overall improved mechanical properties along with low resultant viscosity which can be processed on standard equipment. Shear viscosity along with shear stress of the blends were analyzed using shear rheometer which concluded that the blends can be processed on standard equipment due to resultant low viscosity. Scanning electron microscope micrographs revealed that the morphology of the blends showed a two phase structure in which the minor phase was dispersed as domains in the continuous phase. Polyolefin elastomer (POE) as impact modifier was added to the above composition in the range of 0–15 phr to study its effect. The thermal characteristics of PA6, PEI, and PA6/PEI blends with and without POE were investigated using DSC and TGA which revealed that the melting temperature and crystallization temperature of the blend remained unchanged while XRD results showed percent crystallinity was increased slightly. Furthermore, it can be said that the blend with composition PA6/PEI 75/25 with 10 phr impact modifier loading was suitable for high end applications because it combines the high mechanical properties of glass-filled PA6 with inherent flame-retardant property of PEI while POE overcomes the physical weakness of moisture absorption.     

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.     

Thermal properties of nylon6/ABS polymer blends: Compatibilizer effect

Nylon6/ABS binary blends are incompatible and need to be compatibilized to achieve better performance under impact tests. Poly(methyl methacrylate/maleic anhydride) (MMA-MA) is used in this work to compatibilize in situ nylon6/ABS immiscible blends. The MA functional groups, from MMA-MA copolymers, react with NH₂ groups giving as products nylon molecules grafted to MMA-MA molecules. Those molecular species locate in the nylon6/ABS blend interfacial region increasing the local adhesion. MMA-MA segments are completely miscible with the SAN rich phase from the ABS. The aim of this work is to study the effects of ABS and compatibilizing agent on the melting and crystallization of nylon6/ABS blends. This effect has been investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Incorporation of this compatibilizer and ABS showed little effect on the melting behavior of the PA6 crystalline phase, in general. DMTA analysis confirmed the system immiscibility and showed evidence of compatibility between the two phases, nylon6 and ABS, produced by MMA-MA copolymer presence. The nylon6/ABS blend morphology, observed by transmission electron microscopy (TEM), changes significantly by the addition of the MMA-MA compatibilizer. A better dispersion of ABS in the nylon6 phase is observed.     

Effects of introducing silica particles on the rheological properties and crystallization behavior of poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET)/silica composites were prepared by melt compounding, and their rheological properties and isothermal crystallization were discussed. Introduction of silica particles (0.5–2 wt.%) increased the storage modulus (G′) and decreased loss tangent (tanδ). However, the effect of the particles on rheological properties became negligible at a high frequency more than ca. 70 rad/s. In the Cole–Cole plot, the PET/silica composites showed little deviation from the master curve regardless of the presence of silica particles. The particles increased the relaxation time of PET at particularly low frequency. The isothermal crystallization kinetics of PET/silica was examined using a differential scanning calorimeter (DSC). The half-time of crystallization was decreased with increasing the silica content. The incorporation of silica particles decreased the equilibrium melting temperature by ca. 5.5 °C. In addition, the composites exhibited higher average value of Avrami exponent (2.7–2.9) in comparison with that of pure PET (2.2).     

相容性对PA66/POE共混材料形态、微结构及力学性能的影响

采用SEM、TEM、DSC及材料力学性能实验方法研究了马来酸酐 ( MAH ) 接枝乙烯-辛烯共聚物弹性体 ( POE ) 对PA66/POE共混材料形态、微结构及力学性能的影响。结果表明:热引发官能化POE产物 ( POE-g-MAH ) 可显著改善PA66/POE共混材料的相容性,使材料分散相尺寸减小,分布均匀,且材料缺口冲击强度显著增大。实验发现,PA66/POE-g-MAH共混材料分散相的弹性体颗粒内部存在较多份量的有序结构,材料中的分散相颗粒具有明显促进结晶的作用,此作用引起PA66基体结晶温度增加,结晶度增大,并在分散相质量分数为15% 的脆韧转变条件下,达到极大值。试样熔体的冷却速率越快,则此种促进结晶的作用就越明显。      

高密度聚乙烯/尼龙6共混物的形态结构对其性能的影响

本文利用微层共挤方法制备了具有层状交替结构的HDPE/PA6共混物,利用常规熔融共混挤出方法制备了与层状共混物具有相同组成比的海岛结构共混物。通过DSC,FT-IR及力学性能测试等方法研究了共混物的形态结构对其界面化学反应、结晶行为和力学性能的影响。研究结果表明:在共混物中引入少量马来酸酐接枝高密度聚乙烯时,化学反应在界面进行,与海岛结构的共混物界面面积相比,层状共混物的界面接触面积小,界面化学反应相对较弱,但层状共混物的屈服强度和断裂伸长率有大幅度提高。层状结构对HDPE和PA6的结晶行为影响很小。     

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.     

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     

特殊形态结构导电高分子复合材料的电学性能

先使聚丙烯接枝马来酸酐(PP-g-MAH)与炭黑(CB)反应,再与聚丙烯/尼龙6(PP/PA6)共混制备出CB位于两相界面处的PP/PA6/PP-g-MAH/CB导电高分子复合材料,研究了材料的特殊结构和电学性能。结果表明,在PP/PA6/CB体系中CB粒子分布在PA6相,体系的逾渗阈值为2%;而在PP/PA6/PP-g-MAH/CB体系中,CB被PP-g-MAH诱导分布在两相界面处。PP/PA6两相为海岛结构时,PP/PA6/PP-g-MAH/CB体系仍可导电。PP/PA6/PP-g-MAH/CB体系的逾渗阈值降至1.6%,低于PP/PA6/CB体系。体系的正温度效应(PTC)强度远高于PP/PA6/CB体系,在90-135℃范围内不出现负温度效应(NTC)。PP/PA6/PP-g-MAH/CB体系的电学性能归结于其特殊的界面形态结构:导电通道由位于共混物界面处的PP-g-MAH和CB构建而成。     

界面对ABS/PA6共混体系脆韧转变及断裂行为的影响

合成了反应性核壳结构增韧剂ABS-g-MA和ABS-g-AA增韧PA6, 2种增韧剂的唯一差别在于壳层接枝的反应性单体不同, 从而在与PA6共混过程中相界面存在差异, 研究在其他参数都相同的条件下, 界面性质对ABS/PA6共混体系脆韧转变及断裂行为的影响。Molau试验与扭矩试验证实ABS-g-MA/PA6共混物具有更佳的界面强度。TEM结果表明2种增韧剂在PA6中均匀分散, 然而力学测试结果表明ABS-g-MA/PA6共混物在分散相质量分数为25%~30%时发生脆韧转变,冲击强度可以达到900 J/m以上, ABS-g-AA/PA6共混物在分散相质量分数为30%~35%时发生脆韧转变。SEM结果表明ABS-g-MA/PA6共混物断面发生显著的塑性形变。TEM表明ABS-g-MA/PA6共混物的形变机制为橡胶粒子的空洞化与塑料基体的剪切屈服, 而ABS-g-AA/PA6体系没有空洞化现象, 基体剪切屈服不明显。Vu---Khanh方法测试表明, 由于ABS-g-MA/PA6共混物更高的界面强度, 共混物具有更高的G_i值, 因此冲击韧性极佳。      

Morphological, mechanical and rheological properties of nylon 6/acrylonitrile-butadiene- styrene blends compatibilized with MMA/MA copolymers

The morphological, mechanical and rheological properties of nylon 6/acrylonitrile- butadiene-styrene blends compatibilized with MMA-MA [poly(methyl methacrylate-co- maleic anhydride)] copolymers were studied. A twin screw extruder was used for melt-blended the polymers and the injection moulding process was used to mold the samples. The main focus was on nylon 6/ABS blends compatibilized with one MMA-MA copolymer. This copolymer has PMMA segments that appear to be miscible with the styrene-acrylonitrile (SAN) phase of ABS and the anhydride groups can react with amine end groups of the nylon 6 (Ny6) to form graft copolymers at the interface between Ny6 and ABS rich phases. Tensile and impact and morphological properties were enhanced by the incorporation of this copolymer. Transmission electron microscopy (TEM) observations revealed that the ABS domains are finely dispersed in nylon 6 matrix and led to the lowest ductile-brittle transition temperatures and highest impact properties. It can be concluded that the MMA-MA copolymer is an efficient alternative for the reactive compatibilization and can be used as a compatibilizer for nylon 6/ABS blends.     

Electrical,rheological and morphological studies in co-continuous blends of polyamide 6 and acrylonitrile–butadiene–styrene with multiwall carbon nanotubes prepared by melt blending

Multiwall carbon nanotubes (MWNT) were incorporated in melt-mixed co-continuous blends of polyamide 6 (PA6) and acrylonitrile–butadiene–styrene (ABS) using a conical twin-screw microcompounder. The state of dispersion of MWNT in the blends was assessed through AC electrical conductivity measurements and melt-rheological investigations. The electrical and rheological percolation threshold in PA6/ABS blends was ～3–4 and ～1–2 wt% MWNT, respectively. A unique reactive modifier (sodium salt of 6-amino hexanoic acid, Na–AHA) was employed to facilitate ‘network-like’ structure of MWNT and to confine them in a specific phase. This was achieved by establishing specific interactions with the delocalized ‘π-electron’ clouds of MWNT and melt-interfacial reaction during melt-mixing. The electrical percolation threshold was significantly reduced in the blends (～0.25 wt%) in the presence of Na–AHA modified MWNT and even coincided with the rheological percolation threshold. Significant refinement in the co-continuous structure was also observed in the presence of Na–AHA modified MWNT.     

Specific interactions induced dispersion and confinement of multi-walled carbon nanotubes in co-continuous polymer blends

Multiwall carbon nanotubes (MWNT) were melt-mixed with 50/50 co-continuous blends of polyamide 6 (PA6) and acrylonitrile-butadiene-styrene (ABS). Blending sequence and moulding processes were found to have a strong impact on the conductivity of the blends with MWNT. Aggregated nature of the tubes, migration during processing and skin-core morphology generated during mould cooling step were found to be crucial parameters affecting the electrical conductivity of the blends. We report here the role of a reactive modifier: sodium salt of 6-amino hexanoic acid (Na-AHA) aiding in uniform dispersion of the MWNT in the 50/50 PA6/ABS blends and restricting the tubes utilizing specific interactions during melt-mixing in the PA6 phase in the blends. We further varied the MWNT to Na-AHA ratio from 1:1 to 1:15 to optimize the concentration of MWNT required in achieving lower electrical percolation threshold in co-continuous PA6/ABS blends. The associated percolation threshold was observed at approximately 0.5 wt% MWNT with high dielectric constant.     

The falling weight impact properties of maleic anhydride compatibilized polypropylene–polyamide blends

A series of polypropylene–polyamide 6 (PP–PA) blends of composition 80: 20, 50:50 and 20:80 have been prepared in a twin screw extruder followed by injection moulding. Maleic anhydride grafted polypropylene was used as a compatibilizer for these blends. Static mechanical and falling weight impact tests were performed on these blends. The fracture surfaces of impact specimens were subsequently examined by scanning electron microscopy (SEM). The mechanical properties of the blends were found to be strongly dependent on the PP–PA blend ratios. The Young’s modulus, tensile strength and impact energy were observed to increase with increasing PA content. The impact strength was better in blends when the PA content approached 80 wt %. SEM observations revealed that the addition of compatibilizer resulted in good adhesion between the PP dispersed domains and PA matrix in the PP–PA 20:80 blend. Furthermore, the SEM fractographs also indicated that the cold drawn of PA matrix and debonding of PP domains were responsible for the high impact strength of this blend. This revised version was published online in November 2006 with corrections to the Cover Date.     

马来酸酐共聚方式对PA6/ABS共混物性能的影响

分别制备了马来酸酐与苯乙烯-丙烯腈无规共聚物(SAM)增容的尼龙6(PA6)/ABS/SAM共混物、马来酸酐接枝共聚的丙烯腈-丁二烯-苯乙烯共聚物(ABS-g-MA)增容增韧的PA6/ABS-g-MA共混物。结果表明,两个体系中ABS都可以均匀分散;冲击测试发现样条厚度为6.35 mm时,PA6/ABS-g-MA共混物出现明显的脆韧转变,PA6/ABS/SAM共混物为脆性断裂;样条厚度为3.18 mm时,两个体系都有明显脆韧转变;Vu-Khanh方程表明,PA6/ABS-g-MA共混物具有更高的裂纹扩展能(Gi)和撕裂模量(Ta),性能更好。     

Impact essential work of fracture toughness of ABS/polyamide-6 blends compatibilized with olefin based copolymers

The impact fracture toughness of acrylonitrile-styrene-butadiene/polyamide-6 (ABS/PA6) blends compatibilized with 5% by weight carbon monoxide modified ethylene-n butyl acrylate-maleic anhydride (EnBACO-MAH) or ethylene-methyl acrylate-glycidyl methacrylate (EMA-GMA) copolymers were examined as a function of blend ratio by standard Charpy tests, Essential Work of Fracture (EWF) Methodology and fracture surface morphologies. The samples were first processed in twin-screw extruder and they were subsequently injection moulded. The incompatibilized blends and neat-PA6 fractured in brittle manner, whereas compatibilized blends fractured in ductile manner. The EWF values yielded a maximum when weight percentages of ABS and PA6 were equal to each other. The values obtained in the case of EnBACO-MAH were higher than that of EMA-GMA regardless of blend composition in EWF tests. The trend of impact strengths observed in standard notched Charpy impact tests was in accordance with that of EWF values of blends. The morphology of the ABS/PA6 blends exhibited differences as a function of the component ratio and compatibilizer type. These differences in topology of the fracture surfaces of the blends were utilized to understand the deformation mechanism, and to correlate the fracture toughness values of the blends.     

三种形貌纳米SiO_2的调控合成及其原位增强亲水性聚氨酯注浆复合材料

以硅酸钠为硅源,通过对硅酸钠水解形成纳米SiO_2(nano SiO_2)的过程进行调控,得到含无定形nano SiO_2(nano A-SiO_2)、球状nano SiO_2(nano S-SiO_2)和层状六角形nano SiO_2(nano LH-SiO_2)的水溶胶。以异氰酸酯和高亲水性聚醚多元醇为原料,合成亲水性聚氨酯(HPU)预聚体,并实现其与硅溶胶的原位反应,制备nano SiO_2/HPU注浆复合材料。通过ATR-FTIR、TEM、SEM及力学性能测试,对nano SiO_2/HPU的结构和性能进行表征与测试。结果表明,成功实现了聚乙二醇(PEG)对硅酸钠水解生成nano SiO_2过程的调控,并且不同形态结构的nano SiO_2粒子对nano SiO_2/HPU注浆复合材料的力学性能影响不同。其中,nano S-SiO_2/HPU具有更高的压缩强度,nano LH-SiO_2/HPU具有更强的韧性。