长玻璃纤维增强尼龙6复合材料力学性能的研究

研究以聚丙烯接枝马来酸酐(PP-g-MAH)和聚烯烃弹性体接枝马来酸酐(POE-g-MAH)为界面相容剂的长玻璃纤维增强尼龙6(LGF/PA 6)复合材料的力学性能,并与短玻璃纤维增强尼龙6(SGF/PA 6)复合材料的力学性能进行对比。结果表明:LGF/PA 6复合材料的拉伸强度、弯曲强度和弯曲模量均随着玻璃纤维含量的增加呈直线上升趋势,玻璃纤维质量分数达到40%时,增强效果十分显著;在添加相同含量的玻璃纤维时,LGF/PA 6复合材料的拉伸强度、弯曲强度、弯曲模量低于SGF/PA 6复合材料;2种复合材料的冲击强度均随着玻璃纤维含量的增加呈非线性增加,当添加相同含量的玻璃纤维时,LGF/PA 6复合材料的冲击强度高于SGF/PA 6复合材料;两种界面相容剂均改善了玻璃纤维与PA 6的界面性能,显著提高了复合材料的冲击强度,其中添加PP-g-MAH的LGF/PA 6复合材料的冲击强度的提高高于添加POE-g-MAH的,但拉伸强度和弯曲强度均有不同程度降低,其中添加POE-g-MAH的LGF/PA 6复合材料的拉伸强度、弯曲强度和弯曲模量下降得较为明显。     

Creep behavior of nylon fiber-reinforced asphalt concrete

This study aims to investigate the permanent deformation behavior of asphalt concrete reinforced by nylon fibers. Nylon fibers (12 mm length) have been added to a typical asphalt concrete at different percentages of 0.05, 0.1, 0.15, 0.2, 0.25, and 0.3% (based on total weight of mixture), and the permanent deformation behavior of the mixtures have been investigated by dynamic creep tests at different stress levels of 200 and 400 kPa, and different temperatures of 40, 50, and 60 °C on the mixtures. A three-stage model (developed by Zhou et al.) has been used for modeling the creep curve of the mixtures and determining the flow number and creep strain slope of the mixtures, which are used to describe the permanent deformation of asphaltic mixtures. The parameters of the models were determined in MATLAB using an algorithm established by Zhou et al. The results showed that the mixture reinforced by 0.1% of nylon fibers has the highest resistance to permanent deformation. The three-stage model was well fitted with the dynamic creep test results of the mixtures. The results also showed that the mixture containing 0.1% of nylon fibers has the lowest creep strain slope and the highest flow number, indicating that this mixture has the highest resistance to permanent deformation.     

Fatigue crack growth and fracture in glass sphere-filled nylon 6

The common degrading effect of glass beads on the static fracture energy and the fatigue crack propagation response in nylon 6 materials is examined by conducting fracture mechanics tests and by considering the progress of cracks through the composites. The scanning electron micrographs indicate that the cracks travel through regions of polymer matrix and also along the interfaces between polymer and glass beads. It is demonstrated that, although fracture of the polymer regions requires considerable energy, cracking of the interfaces usually absorbs very little. Thus, the crack propagation is preferably concentrated on these microstructural regions, which is the cause of the decrease in fracture energy and increase in fatigue crack growth rate with increasing amount of glass spheres in the composite. Partial properties of the matrix and the interface are introduced in order to describe the fracture behavior and to improve the understanding of the gross fracture processes. The combination of these partial properties with the volume fraction of filler and certain geometrical factors by a modified rule of mixture leads to critical values for the failure of the composites, which are in reasonable accord with the measured fatigue and fracture data.     

Tensile behavior of glass fiber-reinforced acetal polymer

The tensile stress-strain behavior of glass fiber-reinforced polyacetal resin was investigated for various fiber concentrations, fiber length distributions, and finishing agents. The polyacetal fiber blends change considerably in strength and elongation at break when treated with ammonium chloride, but otherwise similar specimens still follow a common stress-strain curve to a point shortly before failure. As the mean fiber length decreases, the modulus and tensile strength fall, but the elongation at break remains almost unchanged. The observed tensile behavior is discussed in terms of a simplified model, which assigns the fibers to two categories: a fraction α parallel to the applied load, and the remainder distributed in a plane perpendicular to the load axis. By fitting this model to the stress-strain curves, two other constants of each system are derived: a length-dependent efficiency factor β for parallel fibers, whose magnitude agrees with the predictions of Rosen and his co-workers, and a factor γ which expresses the constraint of the matrix resin by the “transverse” fibers. The behavior of γ is consistent with Tsai's theory of the transverse modulus of laminates, if a reasonable amount of fiber–fiber contact is assumed. In terms of this model, possible interpretations of the behavior under repeated loading and the mechanism of tensile failure are presented.     

Impact fracture behavior of injection molded long glass fiber reinforced polypropylene

In this work the variation in Izod impact strength with spatial location was examined for injection molded long glass fiber polypropylene composite plaques. These plaques were fabricated at different sets of processing conditions, with injection speed and melt temperature being varied. By carefully machining test specimens, fifteen different plaque locations both in the in-flow and cross-flow directions were tested. The part morphology was described with the use of characteristic layer thickness ratios, i.e., the shell and the core to part thickness ratios, which were measured experimentally. It was shown that the variation in impact strength with sample location strongly correlates to shell to part thickness ratio. In addition, it was observed that different failure mechanisms exist for different fiber orientations, i.e., for fibers oriented transversely to the crack plane or on the crack plane itself. Scanning electron microscopy (SEM) of the fracture surface was conducted and the results supported our findings on the microstructural level.     

Crystallization behavior of nylon 6 nanocomposites

The crystallization behavior of nylon 6 nanocomposites formed by melt processing was investigated. Nanocomposites were produced by extruding mixtures of organically modified montmorillonite and molten nylon 6 using a twin screw extruder. Isothermal and non-isothermal crystallization studies involving differential scanning calorimetry (DSC) were conducted on samples to understand how organoclay concentration and degree of clay platelet exfoliation influence the kinetics of polyamide crystallization. Very low levels of clay result in dramatic increases in crystallization kinetics relative to extruded pure polyamide. However, increasing the concentration of clay beyond these levels retards the rate of crystallization. For the pure nylon 6, the rate of crystallization decreases with increasing the molecular weight as expected; however, the largest enhancement in crystallization rate was observed for nanocomposites based on high molecular weight polyamides; this is believed to stem from a higher degree of platelet exfoliation in these nanocomposites. Wide angle X-ray diffraction (WAXD) and DSC were further used to characterize the polymer crystalline morphology of injection molded nanocomposites. The outer or skin layer of molded specimens was found to contain only γ-crystals; whereas, the central or core region contains both the α and γ-forms. The presence of clay enhanced the γ-structure in the skin; however, the clay has little effect on crystal structure in the core. Interestingly, higher levels of crystallinity were observed in the skin than in the core for the nanocomposites, while the opposite was true for the pure polyamides. In general, increasing the polymer matrix molecular weight resulted in a lower degree of crystallinity in molded samples as might be expected.     

Mechanical behavior of glass fiber-reinforced Nylon-6 syntactic foams and its Young's modulus numerical study

Glass fiber-reinforced Nylon-6 syntactic foams (GRSF) were fabricated by melt mixing, adding silane-modified hollow glass microspheres (HGMf) at 5, 10, 15, and 20 wt% and an impact modifier at 15 wt. Tensile test results showed that the foam's strength increased with the addition of HGMs but started to decrease when the volume fraction of the spheres was higher than 18 vol% (10 wt%). To elucidate the reinforcement mechanism, a numerical simulation of GRSF was carried out. It revealed that HGMs progressively become the reinforcement phase of GRSFs, as their volume fraction increased due to the load transfer occurring more readily in the HGMs than the fiber, which is expected to be the reinforcement. Hence, for a desired weight-strength ratio, thicker walls are necessary to delay the elastic relaxation of the microspheres and the impairing of the composite as a whole in the context of strength. HGMs with relative wall thickness τ = 0.04 produce an impairing on Young's modulus, if the volume fraction of microspheres is exceeded than 18 vol% because the microspheres are not able to endure increased loads. In addition, a significant reduction of the density was observed by up to 12% in the GRSFs with 30 wt% of both fibers and HGMs. The insight gained of GRSFs role and the numerical simulation achieved through this work, is a significant step toward developing applications of these lightweight materials, since they show good combination of strength, toughness, density, and thermal insulation performance, which can be useful in the automotive, aeronautical and sports industries.     

Polymorphic behavior of nylon 6/saponite and nylon 6/montmorillonite nanocomposites

X‐ray diffraction methods and DSC thermal analysis have been used to investigate the structural change of nylon 6/clay nanocomposites. Nylon 6/clay has prepared by the intercalation of ε‐caprolactam and then exfoliaton of the layered saponite or montmorillonite by subsequent polymerization. Both X‐ray diffraction data and DSC results indicate the presence of polymorphism in nylon 6 and in nylon 6/clay nanocomposites. This polymorphic behavior is dependent on the cooling rate of nylon 6/clay nanocomposites from melt and the content of saponite or montmorillonite in nylon 6/clay nanocomposites. The quenching from the melt induces the crystallization into the γ crystalline form. The addition of clay increases the crystallization rate of the α crystalline form at lower saponite content and promotes the heterophase nucleation of γ crystalline form at higher saponite or montmorillonite content. The effect of thermal treatment on the crystalline structure of nylon 6/clay nanocomposites in the range between Tg and Tm is also discussed.     

Impact fracture behavior of PP/EPDM/glass bead ternary composites

The effects of glass bead filler content and surface treatment of the glass with a silane coupling agent on the room temperature impact fracture behavior of polypropylene (PP)/ethylene‐propylene‐diene monomer copolymer (EPDM)/glass bead(GB) ternary composites were determined. The volume fraction of EPDM was kept constant at 10%. The impact fracture energy and impact strength of the composites increased with increasing volume fraction of glass beads (?_g). Surface pretreatment of the glass beads had an insignificant effect on the impact behavior. For a fixed filler content, the best impact strength was achieved when untreated glass beads and a maleic anhydride modified EPDM were used. The impact strength exhibited a maximum value at ?_g=15%. Morphology/impact property relationships and an explanation of the toughening mechanisms were developed by comparing the impact properties with scanning electron micrographs of fracture surfaces.     

Impact fracture morphology of nylon 6 toughened with a maleated polyethylene–octene elastomer

This study aimed at using scanning electron microscopy to study the Izod impact fracture surface morphology of super‐tough nylon 6 blends prepared by blending nylon 6 with a maleic anhydride‐grafted polyethylene‐octene elastomer (POE) in the presence of a multifunctional epoxy resin (CE‐96) as compatibilizer. The fracture surface morphology and the impact strength of the nylon 6 blends were well correlated. The fracture surface morphology could be divided into a slow‐crack‐growth region and a fast‐crack‐growth region. Under low magnification, the fractured surface morphologies of the low‐impact‐strength nylon 6 blends appeared to be featureless. The area of the slow‐crack‐growth region was small. There were numerous featherlike geometric figures in the fast crack growth region. The fractured surface morphologies of the high‐impact‐strength nylon 6 blends exhibited a much larger area in the slow‐crack‐growth region and parabola markings in the fast‐growth region. Under high magnification, some rubber particles of the low‐impact‐strength nylon 6 blends showed limited cavitation in the slow‐crack‐growth region and featherlike markings in the fast‐crack‐growth region. Rubber particles of high‐impact‐strength nylon 6 blends experienced intensive cavitation in the slow‐crack‐growth region and both cavitation and matrix shear yielding in the fast‐crack‐growth region, allowing the blends to dissipate a significant amount of impact energy. A nylon 6 blend containing 30 wt % POEgMA exhibited shear yielding and a great amount of plastic flow of the matrix throughout the entire slow‐crack‐growth region, thus showing the highest impact strength. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1285–1295, 2000     

Crystallization behavior of PIPD/nylon 6 blends

Blends of poly‐ε‐caprolactam (nylon6) and poly{2,6‐diimidazo[4,5‐b:4′5′‐e]pyridinylene‐1,4(2,5‐dihydroxy) phenylene} (PIPD/nylon 6) have been prepared via a controlled polymer solution crystallization method. The crystallization behavior of nylon 6 in the blends was investigated using differential scanning calorimetry (DSC), x‐ray diffraction (XRD), and polarizing microscopy (PLM). The results indicated that the presence of PIPD inhibited the nucleation rate of the crystallization of nylon 6, resulting in reduction in crystallization temperature, degree of crystallinity, and the perfection of crystal. Such influence was attributed to the formation of hydrogen bonds between nylon 6 and PIPD molecules. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Polymerization and crystallization behavior of anionic nylon 6

The kinetics of the activated anionic polymerization of caprolactam to nylon 6 was studied by the adiabatic temperature rise technique. This allowed very rapid reaction conditions to be studied. The polymerization was activated by diisocyanate and catalyzed by sodium caprolactamate, produced in situ by the addition of sodium hydride. The temperature rise measurements were used to generate Arrhenius curves of the rate data. Several isocyanates were investigated, all giving similar rate curves. The reaction rate was reduced, however, when the activator concentration exceeded the catalyst concentration. To model the actual rapid molding conditions, time vs. temperature reaction profiles were measured for thin plaque castings. In these reaction profiles, two successive exotherms were observed. The first was the polymerization exotherm, and the second was determined to be the crystallization peak. This second exotherm allowed the direct observation of crystallization times within the closed molds. The crystallization times were found to depend strongly on the mold temperature and to a lesser extent on the monomer temperature. The crystallization times were minimized at a 150°C mold temperature. At higher temperatures, the crystallization rate was significantly slower, while at lower temperatures, the slow rate of polymer formation delayed the onset of crystallization. This study has demonstrated the value of using temperature monitoring as a means of studying the polymerization and crystallization behavior of nylon.     

Dynamic viscoelastic behavior of styrene-grafted nylon 6 fiber

Styrene-grafted nylon 6 fibers which had been prepared by the UV irradiation method were investigated by dynamic viscoelasticity and dilatometry. It was found that nylon 6 is relaxed and polystyrene is simultaneously plasticized by nylon 6 during grafting. These phenomena are interpreted as follows. The grafting process causes nylon 6 to have a lower glass transition temperature and increases grafting frequency of polystyrene to nylon 6 by increasing the chemical junctions between the two components, so that they necessarily become more compatible.     

Thermal conductivity and thermal expansion behavior of glass fiber-reinforced rigid polyurethane foam

The thermal conductivities and the thermal expansion curves of glass fiber-reinforced rigid polyurethane foams with various fiber lengths, various fiber volume fractions and various matrix densities were determined experimentally. Additionally the thermal expansion coefficients of these materials at room temperature were examined in terms of the interaction between fiber and matrix. The thermal expansion properties were analyzed successfully with the analogous treatment which is applied to the mechanical tensile behavior.     

The fracture behavior of rubber-toughened,short-fiber composites of nylon 6,6

This study critiques the use of both rubber particles and short-glass fibers for the improvement of polymer fracture toughness (K_c). Although dry neat nylon is brittle with only a moderate K_c value (4.2 Mpa√m), additions of either second phase produce rising K_R-curves and associated high K_c values (8.1 Mpa√m for rubber-toughened nylon, and 10.0Mpa√m for 17 vol% Glass-fiber neat nylon). In the rubber -modified resin, the high K_c value is associated with extensive plastic blunting at the crack tip. In the fiber-reinforced neat resin, K_c is improved due to a combination of fiber-bridging and increased strength, the latter being associated with additional load carrying capacity of the fibers. When both rubber and fibers are added, however, no further increase in K_c is noted (K_c = 9.3 Mpa√m for 17 vol% glass-fiber rubber-modified nylon). The extent of ductile blunting in the rubber + fiber resin is not as great as in the rubber-only resin. Furthermore, the fracure strength of the rubber + fiber resin is not as high as the fiber-only resin. The net result is a balance of properties for the rubber-toughened composite.     

The effect of the secondary relaxations on the fracture toughness of nylon 6/amorphous nylon 6IcoT blends

The fracture toughness of semicrystalline nylon 6, amorphous nylon 6IcoT, and their blends can be represented as the inherent toughness plus the toughness due to the formation of the crack tip plastic zone. The inherent toughness originates mostly from the molecular alignment near the crack tip plus a small contribution from chain scission. The plastic zone contribution is determined by its size and the energy dissipated by irreversible plastic deformation. The inherent toughness and the energy dissipated in the process zone are temperature dependent and primarily determined by the stress-induced molecular movement, which is related to the operative secondary β or γ relaxation.     

Thermal behavior of nylon 6 copolyamides containing aromatic rings

The thermal behavior of terpolymers of caprolactam (CL) and of hexamethylenediammonium isophthalate (IH) and terephthalate (TH) has been studied in a wide range of compositions by differential thermal analysis. It has been found that either amorphous or crystalline polymers having different crystallization rates can be obtained by changing the composition. The dependence of melting points and glass transition temperatures on the composition has been investigated. The dependence of T_g on the composition for the copolymers CL–IH, IH–TH, and CL–TH has been described by means of the Gordon-Taylor equation. It has been found that this equation fits the experimental data for the IH–TH system only if a parameter which takes into account interactions between the monomeric units is introduced. A ternary iso-T_g map has been obtained through statistical analysis. The influence of the chain stiffness and bulkiness of the monomers on the glass transition temperature is discussed.     

The production of glass fiber-reinforced poly(butylene terephthalate) on a continuous kneader

In poly(butylene terephthalate) based compositions, thermal degradation of the polymer matrix during processing has to be minimized to achieve quality products. Experience has shown a temperature-residence time relationship, indicating that for mixing systems with high product temperatures, the residence time of the product has to be reduced to avoid excessive thermal degradation. The power density of the mixing system is related to the specific energy input and the residence time of the product. From rheology, the power density is also known for a simple shear deformation which can thus be used to characterize the shear intensity of a particular mixing process. Comparing two different mixing systems by their power density provides us with a qualitative better understanding why higher shear is permitted with lower residence time. From theoretical considerations it was found that for a temperature-sensitive product, like PBT, the power density in the mixing operation can be further raised, taking into account that with shorter residence time a higher product temperature is permitted. Production-scale test work was carried out on a 200 mm screw-diameter continuous kneader to investigate the effect of running conditions and screw design on the thermal degradation of two different types of PBT. Results have shown that for the high-viscosity PBT a linear relationship exists between product temperature and the viscosity retained upon compounding. In a two-stage kneader only minor thermal degradation is encountered in the melting section, but conditions become critical in the mixing stage due to the viscosity increase after introducing the glass fibers to the melt. A new feature in compounding thermodegradable products is the addition of unmolten polymer into the mixing stage of the kneader since this leads to a reduction in the product end temperature and, consequently, thermal degradation of the matrix material. The limited results obtained so far indicate that an optimum exists as to the amount of pellets added. At a 15 percent level the product temperature was reduced by 20°C as compared to 10°C at 20 percent. An energy balance carried out on the continuous kneader indicates that because of the low melt viscosity approximately 30 percent of the energy put into the product in the melting section of the kneader originates from external heating. A rough comparison shows that the power density of a continuous kneader is twice that of a single-screw extruder designed for compounding PBT, but, can be tolerated because of the considerably lower residence time in the former mixing system.     

Interlaminar fracture toughness and fatigue fracture of continuous fiber-reinforced polymer composites with carbon-based nanoreinforcements: a review

ABSTRACT

This review critically examines the recent developments in the use of carbon-based nanofillers as additional reinforcement to enhance the interlaminar properties of FRP composites. The low interlaminar strength of FRP composites results in delamination failure. The various nanoreinforcement strategies and their effect on fracture toughness, interlaminar shear strength (ILSS) and interlaminar fatigue are discussed in detail to prevent this delamination failure. Important findings on various factors that influence the interlaminar properties of multi-scale composites are presented by discussing various intrinsic and extrinsic toughening processes. Moreover, an overview of simulation techniques is provided to predict the delamination onset and propagation.