Effect of absorbed water on dynamic modulus for short fiber–CR composites

Short fiber–elastomer composites with 10 vol % fiber, nylon 6–CR and PET–CR composites, absorbed water either in the moisture atmosphere or in water. The effect of absorbed water on the viscoelastic properties for these composites was investigated. The temperature dependence of tan σ for the nylon–CR composite showed that the α-dispersion peak of nylon shifted to lower temperatures with increasing absorbed water content and that after displacement of the α-dispersion peak the additional small hump appeared at about 90°C. For the PET composite, the α-dispersion peak of PET shifted slightly to lower temperatures and the small shoulder at 90°C diminished with increasing absorbed water. The additional dispersion probably was caused by the interface between fiber and CR matrix and was independent of fiber orientation. The results suggested that nylon fiber absorbed a larger amount of water than CR matrix, while the water absorption for PET fiber was considerably less than for nylon fiber. The absorbed water in nylon fiber bonded stronger than that in CR matrix and was only slightly diminished by heat treatment under 100°C.     

Properties of a polyamide thermoplastic based on 2,2-bis-(4-aminocyclohexyl)propane

The structure and properties of an unusual new polyamide copolymer derived from 2,2-bis-(4-aminoeyclohexyl)propane and a 60/40 molar mixture of azelaic and adipic acids are described. The alicyclic diamine structure, with its cyclohexyl rings and central gem-dimethyl group, contribute to chain stiffness and amorphous character in the polyamide, and sets it apart from more common polyamides (e.g., nylon 6–6) with their relatively flexible polymer chains, low glass transition temperatures and high levels of crystallinity. The particular combination of dicarboxylic acids employed yields a resin with a high glass transition temperature (185°C). This amorphous, colorless material is exceptionally transparent, with a high luminous transmission (92 percent) and low haze (0.5 percent). The polymer is tough and resistant to scratching and abrasion and to attack by chemicals and solvents. Its high glass transition temperature leads to a high heat deflection temperature (160°C) and excellent retention of its mechanical properties at elevated temperatures. It is an atypical nylon in that its dimensions, mechanical properties and electrical properties are relatively unaffected by changing moisture content.     

Effect of moisture absorption on the dynamic mechanical properties of short carbon fiber reinforced nylon 6, 6

A study of hygrothermal aging in terms of the kinetics of moisture absorption by nylon 6,6 and its carbon fiber reinforced composites has been carried out. The single free phase model of absorption has been applied to the kinetic data and thereafter the values of diffusivity have been evaluted. The diffusivity was found to be dependent on the conditioning temperatures and the volume fraction of fibers. Dynamic mechanical properties of unaged and aged samples were studied using a free resonance torsion pendulum which covers a temperature range of 350°C. Incorporation of carbon fibers has led to an increase in structural rigidity of the nylon 6,6 matrix especially at higher temperatures. This was reflected by the sharp increase in the relative shear modulus as the glass transition temperature of nylon 6,6 is appoached. Absorbed moisture was observed to plasticize the polymer matrix and decreased the temperatures of all the transitions. For instance, the α-transition was shifted by almost 95°C. The intensities of the transition peaks of both unaged and aged samples were found to decrease with fiber volume fraction. Increasing the conditioning temperatures has resulted in a reduction of the shear storage modulus and this effect was found to be more pronounced in the reinforced nylon 6,6. This has been attributed to the increase in the extent of degradation at the fiber-matrix interface.     

Polymerization of allyl methacrylate with nylon 6 using benzoyl peroxide as initiator

Polymerization of allyl methacrylate with nylon 6 using benzoyl peroxide as initiator was carried out under different conditions. The polymer add-on was dependent upon allyl methacrylate and benzoyl peroxide concentrations, polymerization time and temperature as well as addition of metallic salts or organic solvents. The polymer add-on increased by increasing benzoyl peroxide concentration up to 0.5 mmol/l then decreased by further increase in peroxide concentration, whereas it increased as the allyl methacrylate concentration increased from 80 – 300 mmol/l. A polymerization temperature of 85°C constituted the optimal temperature, below or above this temperature resulted in lower polymer add-on. The effect of polymerization time was related to the polymerization temperature, no induction period occured at 95°C in contrast to 15 and 30 minutes at 85°C and 75°C, respectively. The incorporation of Cu^{+ +}ions in the polymerization system improved the magnitude of polymer add-on. A similar situation was encountered with Fe^{+ + +} and Li⁺ ions. Using a water/organic solvent mixture as a polymerization medium was advantageous in enhancing polymer add-on provided that the organic solvent did not exceed 1% in case of ethanol and isopropanol and 4% in case of methanol.     

Anionic copolymerization of nylon 6/12: A comprehensive review

This review aims to provide a concise insight into the rapidly growing anionic ring‐opening copolymerization of nylon 6/12 and its related structures. This study analyzes the relationship between the structures of polymerization components and the relevant properties to achieve optimum copolymerization formulation. Specific emphasis is placed on how the catalyst type and temperature influence the final copolymer structure. The present work reviews available literature about nylon 6/12 synthesis published between 1960 and 2017 and investigates structures linked to polymerization mechanisms behind them. Moreover, experimental results derived from direct/indirect identification methods of structures are presented. The crystalline morphology of different structures was also evaluated. The thermal behaviors of synthesized copolymers are explored comprehensively. Finally, mechanical properties alteration and enhanced water absorption results are reported. POLYM. ENG. SCI., 59:1529–1543 2019. © 2019 Society of Plastics Engineers     

Processing and properties of poly(p-phenylene benzobisthiazole)/nylon fibers

Composite fibers of poly(p-phenylene benzobisthiazole) (PBT) with nylons were spun from dilute acid solutions. The effects of wet-stretching, heat treatment time, tension, and temperature on the tensile properties are reported. Nylon 6,6 and nylon 6 at several molecular weights were studied. Moduli of 40 GPa and tensile strengths of 375 MPa were achieved for 30/70 PBT/nylon composites. Heat treatment of the nylon/PBT fibers at 160–225°C for 12–19 h increased the tensile modulus by 20–50% and the tensile strength by a smaller amount. At the same time, the intrinsic viscosity of the nylons increased as much as 100%, indicating the solid-state polymerization of the nylon. The largest tensile modulus attained is less than half the theoretical value predicted by a linear “rule of mixtures” as might be expected for an oriented molecular composite. Although differential scanning calorimetry shows a melting transition at temperatures 5–10°C higher than the pure nylons, the composite does not flow at temperatures above this transition. Sulfuric acid dissolves most of the nylon, but does not destroy the mechanical integrity of the fibers; differential scanning calorimetry indicates that the remaining fiber contains little or no nylon. The results are consistent with a microstructure consisting of a microfibrillar network of PBT, surrounded by a separate nylon phase.     

尼龙6/纳米蒙脱土复合材料制备及性能研究

利用活化处理的纳米蒙脱土(OMMT),通过原位插层聚合原理,控制聚合温度、压力、时间等,在聚合管实现连续化稳定制备剥离型尼龙6(PA6)/纳米OMMT复合材料;采用熔融纺丝法制得PA6/纳米OMMT复合纤维;利用X射线衍射、透射电镜(TEM)等方法分析复合材料的结构与性能。结果表明:聚合时控制水与己内酰胺质量比为3%～5%,前聚压力不超过0.4 MPa,后聚压力小于-0.040 MPa,聚合温度240～280℃,聚合时间26～30 h,可制得相对分子质量为18 000～18 600,单体质量分数小于1.6%,含水率小于450μg/g的PA6/纳米OMMT切片;TEM分析表明,纳米OMMT在PA6基体均匀分散;复合材料的力学性能有较大幅度的提高,断裂强度达102.15 MPa,比纯PA6提高了12%;PA6/纳米OMMT复合纤维性能优异,适合轮胎骨架材料的制备要求。     

Preparation and characterization of polyamide‐6 with three‐branched chains

With trimesinic acid as a molecular weight regulator, the hydrolytic polymerization of ?‐caprolactam was carried out, and nylon‐6 or polyamide‐6 with three‐branched chains was obtained. Through a systematic study of the effects of conditions such as the reaction time and concentration of trimesinic acid on the polymerization, we found that the conversion of caprolactam was almost insensitive to the initial concentrations of the regulators, but the relative viscosity of the polymer decreased with increasing trimesinic acid. Characterization investigations showed that differential scanning calorimetry curves changed from a single peak for normal nylon‐6 to one main peak and one shoulder or one small peak for the branched polymer; the melting point of the star‐shaped nylon‐6 decreased with an increasing amount of trimesinic acid, whereas its crystallization temperature was higher than that of linear‐chain nylon‐6. A wide‐angle X‐ray diffraction study indicated that the crystal structure of the star‐shaped nylon‐6 still belonged to the α form, and the crystallizability of the branched polymer with an elevated amount of trimesinic acid during polymerization did not seem to be weakened; the characteristic absorption of infrared spectra provided indirect evidence for the existence of branched chains in the polymer. Moreover, the mechanical properties of star‐shaped nylon‐6 and linear‐chain nylon‐6 were compared. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3184–3193, 2001     

PA6/蒙脱土纳米复合材料的力学性能研究

利用未改性蒙脱土和两种季胺盐改性蒙脱土与尼龙(PA)6混合,成功制备得到了不同结构的PA6/蒙脱土纳米复合材料.X射线衍射图谱和力学性能分析表明,季胺盐改性剂可以插入蒙脱土片层之间,使蒙脱土片层扩张,层间距增大.与PA6相比,制备得到的三种纳米复合材料的力学性能都有不同程度的提高.改性蒙脱土与PA6表现出良好的相容性,...     

Structural causes of the dyeing variations of nylon yarns subjected to steam heat

Nylon 6 and nylon 6.6 yarns were subjected to wet heat in a relaxed state and the subsequent rate of dyeing of these yarns with Durazol Blue 2R was then studied. The rate of dyeing progressively increased as the temperature of steaming increased. For nylon 6 this increase in rate of dyeing was almost eightfold in heating up to 140°C compared with that of unheated samples; for nylon 6.6 the increase was threefold after heating in steam at 150°C. It was confirmed that Fick's law is still valid for describing the dyeing process with nylon 6.6 but not with nylon 6. Measurements of density, birefringence, X-ray orientation and degree of lateral order by an X-ray method show that these are all increased by the steam treatments. There is little change in the moisture regain and amine end-group content. An explanation of these observations is advanced in terms of a morphology that allows an increase in the size, shape or quantity of voids on heating the polyamides in steam.     

Dynamic mechanical properties of extruded nylon–wood composites

Dynamic mechanical properties determine the potential end use of a newly developed extruded nylon–wood composite in under‐the‐hood automobile applications. In this article, the dynamic mechanical properties of extruded nylon–wood composites were characterized using a dynamic mechanical thermal analyzer (DMTA) to determine storage modulus, glass transition temperature (T_g), physical aging effects, long‐term performance prediction, and comparisons to similar products. The storage modulus of the nylon–wood composite was found to be more temperature stable than pure nylon 66. The T_g range of the nylon–wood composite was found to be between 23 and 56°C, based on the decrease in storage modulus. A master curve was constructed based on the creep curves at various temperatures from 30 to 80°C. The results show that the relationship between shift factors and temperature follows Arrhenius behavior. Nylon–wood composites have good temperature‐dependent properties. Wood fillers reduced the physical aging effects on nylon in the wood composites. The comparison of the nylon–wood composite with other similar products shows that nylon–wood composites are a promising low cost material for industrial applications. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Sorption of water by nylon 66 and kevlar 29. Equilibria and kinetics

The sorption of water by nylon 66 and Kevlar 29 fabrics was studied over a range of 20–98% relative humidities at 27°C. Equilibrium and rate relationships were developed from the data in this study and from nylon 66 and nylon 6 data of other studies involving fiber and film. The ratio of sorbed moisture to amide concentration is, on average and at high relative humidities, one water molecule per amide unit. The nylon equilibrium data show that there exist threshold relative humidities above and below which sorption properties differ. One threshold is correlated with the glass transition. Another is identified in the glassy state of nylon 6 in which moisture is tightly bound. The equilibrium constant values are highest and the moisture is most tightly bound at very low humidities, and the values are lowest in the plastic region at high humidities. NMR, DSC, and mechanical property data from others are correlated with the sorption discontinuities observed in this study. Rate data indicate that sorption is a diffusion-controlled process.     

Simultaneous enhancements of mechanical and thermal properties of monomer cast nylon via kaolin modified by poly (ethylene glycol diglycidyl ether)

Monomer cast nylon was incorporated with different contents of kaolin, which is grafted with poly (ethylene glycol diglycidyl ether) via in-situ polymerization. The influence of treated-kaolin and kaolin contents on composites properties was studied. Treated-kaolin has a better effect on the properties of nylon than kaolin. Thermogravimetric analysis and Differential scanning calorimetry analysis show that that the feeding of kaolin improved thermal stability and crystallinity of nylon. The results indicate that using treated-kaolin as reinforcement, the composites displayed remarkable mechanical properties, the tensile strength and notched impact strength are 83.6 MPa and 4.46 MPa, respectively. The water absorption capacity of composites was greatly reduced by 50% with the feeding of kaolin.     

Hygrothermal aging studies of short carbon fiber reinforced nylon 6.6

A study of hygrothermal aging, in terms of the kinetics of moisture absorption by nylon 6.6 and its carbon fiber-reinforced composites, has been undertaken. The diffusion of water into the various materials was investigated at 100% relative humidity, by immersion of specimens in water at temperatures of between 25 and 100°C. A mathematical treatment used in analyzing the data was that of a single free phase model of diffusion, which assumed Fickian diffusion and utilized Fick's second law of diffusion. Good agreement was observed between the experimental and theoretical values. The equilibrium moisture content and the apparent diffusion coefficient of the various composites were evaluated. Hygrothermal aging has reduced the tensile properties of both unreinforced and reinforced nylon 6.6, albeit a better recoverability of the properties was achieved by the former after drying. This behavior is explained in terms of the combined action of moisture-induced plasticization and interfacial degradation. © 1994 John Wiley & Sons, Inc.     

Copolyamides derived from brassylic acid

Polyamides were prepared from C₆ to C₁₂ diamines with brassylic acid, a linear C₁₃ dicarboxylic acid, derived from Crambe seed oil. One distinct characteristic of these polymers is their low moisture adsorption as compared to nylon 66 and nylon 6. To modify the properties of these nylons, multi-component copolyamides were prepared from hexamethylene diamine and mixtures of brassylic acid with adipic, terephthalic, or isophthalic acids. It was found that the melting points of the co-polyamides were changed by the choice and the levels of the diacids used. The melting point-composition curves all show a eutectic minimum. The glass transition temperature of nylon 6,13 is also changed by the incorporation of other diacids. Water adsorption of nylon 6,13 increases with increased substitution of brassylic acid by other diacids in the order of adipic > isophthalic ≥ terephthalic. Mechanical properties of some copolyamides are in the same range as the commercial nylon 11 and nylon 12. The low moisture absorption, reduced fabrication temperature, and the wide range of properties obtainable through copolymerization make copolyamides derived from brassylic acid potentially suitable as specialty tubing, powder coatings, and molded machine parts. They will be commercially viable when brassylic acid becomes available on a large scale and is competitively priced.     

Some physical properties of acrylamide and acrylonitrile grafted nylon 6

Graft copolymerization of acrylamide and acrylonitrile on nylon 6 swollen in formic acid (60%) for 30 min was performed using ceric ions as initiator at 60°C. The optimum conditions to get highest percentage of graft-on were utilised to prepare the grafted samples with various amounts of polymer deposited inside the fibres. The mechanical properties, moisture regain, density, infrared studies, birefringence, dye uptake and dynamic mechanical properties were determined for the grafted samples and the results are discussed in relation to possible structural changes due to graft copolymerisation.     

Phase continuity in polystyrene–nylon 6,10 graft copolymers

Using a modified interfacial polymerization route, a graft copolymer of nylon 6,10 and polystyrene was prepared. First, an aqueous suspension of styrene monomer was encapsulated with nylon 6,10, followed by polymerization of the styrene to form the graft copolymer. When the material was subsequently molded below the crystalline melting point of nylon 6,10 (220°C), modulus–temperature behavior intermediate between polystyrene and nylon 6,10 was observed. However, when this graft copolymer was molded above the melting point of nylon 6,10, behavior more like pure polystyrene was observed. Phase contrast microscopy revealed that material molded below 220°C showed a continuous cellular-phase structure of about 30 microns in diameter, the interior of the cells being composed of polystyrene and the cell walls being composed of nylon 6,10. Phase inversion phenomenon was observed in the graft copolymer as the molding temperature was raised above 220°C. The nylon 6,10 phase became discontinuous, small globules being formed. This behavior is analogous to spheroidization in steel. It is thought that molten nylon 6,10 spheroidizes to attain a lower surface-energy state.     

Effects of alkaline conditioning and temperature on the properties of glass fiber polymer composite rebar

This article investigated long term alkaline conditioning and temperature on the physical and mechanical properties of glass fiber‐reinforced polymer (GFRP) composite rebar for structural applications. The GFRP rebar was immersed in alkaline solution (pH ≈ 13) for 23 months at 23°C, and for 24 months at 60°C. The moisture absorption was found to be 0.34% at 23°C after 23 months, and 0.76% at 60°C after 24 months. At both temperatures, moisture absorption did not reach equilibrium which was attributed to two stages non‐Fickian behavior. Glass transition temperature (T_g) of the polymer matrix of rebar that conditioned at 23°C was found to be decreased because of plasticization, whereas T_g of the rebar that conditioned at 60°C was remained greater than the T_g of control rebar due to nonplasticization effect. Shear strength was retained by 83.5% at 23°C and 80.5% at 60°C, flexural strength was retained by 81% at 23°C and 69% at 60°C, and tensile strength was retained by 91.2% at 23°C and 74.3% at 60°C. It was revealed that durability of GFRP rebar in alkaline environment was controlled by the absorbed moisture; this was because the load transfer efficiency of fiber/matrix interface is vulnerable to moisture. POLYM. COMPOS., 37:3181–3190, 2016. © 2015 Society of Plastics Engineers     

Characterization of a rigid silicone resin

Silicone resins have been used as binders for ceramic frit coatings and can withstand temperatures of 650°C to 1260°C. Conceptually, silicone resins can potentially be used as matrices for high temperature fiber‐reinforced composites. The mechanical and thermal properties of a commercially available silicone resin, Dow Corning® 6‐2230, were characterized. Neat 6‐2230 resin was found to have inferior room temperature mechanical properties such as flexural, tensile and fracture properties when compared to epoxy. The room temperature flexural properties and short beam shear strength of the silicone/glass composites were also found to be lower than those of epoxy/glass composite with similar glass content. However, the silicone resin had better elevated temperature properties. At an elevated temperature of 316°C, the retentions of flexural modulus and strength were 80% and 40% respectively of room temperature values; these were superior to those of phenolic/glass. Unlike the carbon‐based resins, the drop in flexural properties of the silicon/glass laminates with temperature leveled off with increase in temperature beyond 250°C. The resin weight loss at 316°C in 100 cm³/min of flowing air was small compared to other carbon‐based resins such as PMR‐15 and LaRC TPI. Only Avimid‐N appeared comparable to Dow Corning® 6‐2230.     

Synthesis and properties of poly(ethylene-1,4-cyclohexanedimethylene naphthalate)

Copolyesters were synthesized from bis(hydroxyethyl) naphthalate/bis(hydroxymethylcyclohexane)naphthalate (BHEN/BHCN) with various compositions. Copolyesters having intrinsic viscosities of 0.58–0.65 dL g were obtained by melt polycondensation in the presence of metallic catalysts. The optimum condition for polyethylene-1,4-cyclohexanedimethylene naphthalate (PECN) copolyester manufacturing is the transesterification under a nitrogen atmosphere for 4 h at a temperature of 245 ± 5°C followed by polymerization under 2 mmHg for 50 min at a temperature of 290–320°C. Most copolyesters have better thermal stability than has poly(ethylene naphthalate) (PEN) and the effect of the cyclohexane–dimethylene structure on the thermal and crystalline properties of the resulting copolyesters was investigated using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Glass transition temperatures of the copolyesters were in the range of 115.2–138.4°C, and 10% weight losses in nitrogen were all above 453°C. The solubility, crystallinity, and moisture absorption of the copolyesters were also investigated. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2245–2252, 1998