Osami Kamigaito

Mechanical properties of nylon 6-clay hybrid

Various nylon 6-clay hybrids, such as molecular composites of nylon 6 and silicate layers of montmorillonite and saponite, NCHs and NCHPs, respectively, have been synthesized. To estimate the mechanical properties of these hybrids, tensile, flexural, impact, and heat distortion tests were carried out. NCH was found superior in strength and modulus and comparable in impact strength to nylon 6. The heat distortion temperature (HDT) of NCH (montmorillonite: 4.7 wt. %) was 152 °C, which was 87 °C higher than that of nylon 6. In NCHP, saponite had a smaller effect on the increase of these mechanical properties. The modulus and HDT of NCH and NCHP increased with an increase in the amount of clay minerals. It was found that these properties were well described by the contribution of the constrained region calculated from the storage and loss modulus at the glass transition temperature. According to the mixing law on elastic modulus, the following expression was obtained between the modulus E at 120 °C and the fraction of the constrained region C, E n = E c n = C , where the values of n and E c (modulus of the constrained region) were 0.685 and 1.02 GPa, respectively.

Synthesis of nylon 6-clay hybrid

It was found that montmorillonite cation exchanged for 12-aminolauric acid (12-montmorillonite) was swollen by ∊-caprolactam to form a new intercalated compound. Caprolactam was polymerized in the interlayer of montmorillonite, a layer silicate, yielding a nylon 6-clay hybrid (NCH). The silicate layers of montmorillonite were uniformly dispersed in nylon 6. The carboxyl end groups of 12-aminolauric acid in 12-montmorillonite initiated polymerization of ∊-caprolactam, and as 12-montmorillonite content became larger, the molecular weight of nylon was reduced. From the result of end-group analysis, carboxyl end groups were more than amino end groups. The difference between the carboxyl and the amino end groups was attributed to ammonium cations (-NH 3 + ) of nylon molecules, because the difference agreed with the anion site concentration of the montmorillonite in NCH. It is suggested that the ammonium cations in nylon 6 interact with the anions in montmorillonite.

Swelling behavior of montmorillonite cation exchanged for ω-amino acids by -caprolactam

Natural Na-montmorillonite was cation exchanged for the ammonium cations of various ω-amino acids [H 3 N + (CH 2 ) n −1 COOH, n = 2, 3, 4, 5, 6, 8, 11, 12, and 18]. X-ray diffraction (XRD) results suggested that the chain axes of ω-amino acids with a carbon number of eight or less were parallel to the silicate layers, and that the chain axes of those with a carbon number of 11 or more were slanted to the layers. The cation-exchanged montmorillonites form intercalated compounds with ∊-caprolactam at 25 °C. The montmorillonites intercalated with both ω-amino acid and ∊-caprolactam were studied by XRD measurement at room temperature and 100 °C. We propose a model where amino acid molecules were arranged perpendicular to silicate layers and ∊-caprolactam molecules filled the space between them. When the ∊-caprolactam was melted at 100 °C, the basal spacing for the montmorillonite increased, in which the carbon number exceeds 11. This phenomenon will be applicable to obtaining the nylon 6-clay hybrid, a molecular composite of nylon 6 and montmorillonite.

Nylon 6–Clay Hybrid

ζ-Caprolactam was polymerized in the interlayer spacing of montmorillonite, a clay mineral, yielding a nylon 6-clay hybrid (NCH) 1) . X-ray and TEM measurements revealed that each template of the silicate, which is 10 A thick, was dispersed in the nylon 6 matrix and that the repeat unit increased from 12 A in unintercalated material to 21 A in the intercalated material. Thus NCH, is a “polymer based molecular composite” or “nanometer composite”. NCH, when injection-molded, shows excellent properties as compared to nylon 6 in terms of tensile strength, tensile modulus and heat resistance. Heat distortion temperature increased from 65 °c for nylon 6 to 152 °c for NCH, containing 4 wt% (1.6 vol%) of clay mineral.

Mechanical property changes in sapphire by nickel ion implantation and their dependence on implantation temperature

Sapphire plates, cut parallel to an {0001} plane, have been implanted with 300 keV nickel ions to doses ranging from 5×1012 to 1×1017 Ni cm−2 at specimen temperatures of 100, 300 and 523 K, in order to investigate the effect of implantation temperature on the mechanical property changes in sapphire caused by ion implantation. The measured changes in surface hardness, surface fracture toughness and bulk flexural strength were found to depend strongly on the implantation temperature, and were largely correlated with the residual surface compressive stress measured by using a cantilever beam technique. The surface amorphization that occurred only by the implantation at 100 K and at doses larger than ∼2×10s15 Ni cm−2 reduced the hardness to ∼0.6 relative to the value of the unimplanted sapphire, and considerably increased the surface plasticity. Furthermore, the amorphization was found to involve a large volume expansion of ∼30% and to change drastically the apparent shape and size of a Knoop indentation flaw made prior to implantation. This effect was suggested to reduce stress concentrations at surface flaws and hence to increase the flexural strength.

MICROFAILURE BEHAVIOUR OF RANDOMLY DISPERSED SHORT FIBRE REINFORCED THERMOPLASTIC COMPOSITES OBTAINED BY DIRECT SEM OBSERVATION

The microfailure behaviour of thermoplastic polyamide 6,6 composites reinforced with randomly dispersed short glass fibres was studied. Scanning electron microscopy was carried out on the surface of the composites under load to observe directly the behaviour. The microfailure proceeds following the steps (1) interfacial microfailure occurs at the fibre tips, (2) the microfailure propagates along the fibre sides, (3) plastic deformation bands of the matrix occurs from the interfacial one, (4) crack opening occurs in the band and the crack grows slowly through the band, (5) finally a catastrophic crack propagation occurs through the matrix with pulling-out fibres from the matrix. A model for the microfailure mechanism of the composites is proposed and some methods to improve the mechanical properties of the composites are discussed on the basis of the mechanism.

Mechanism of fracture of short glass fibre-reinforced polyamide thermoplastic

The mechanism of fracture of short glass fibre-reinforced polyamide 6.6 thermoplastic was studied by means of optical and electron microscopy and acoustic emission methods. It was found that there were three stages in the failure, i.e. initiation of the interfacial cracks at fibre ends, propagation of the interfacial cracks along fibre sides, and propagation of the crack into the matrix leading to the failure of the composite. On the fracture surface, fibres were almost pulled-out from the matrix, not broken. The close correspondence between the crack initiation and propagation and the amplitude of AE signals was observed. The AE signals of lower amplitude occurring under a relatively low stress were considered to be made in association with the initiation and propagation of the interfacial cracks. The AE signals of higher amplitude observed prior to the failure of the composite were considered to be made in association with the occurrence of the matrix cracks. Furthermore, in order to analyse the effect of the stress state in the composite on crack occurrence and propagation, the stress levels in matrix, fibre and interface were estimated for the composite stressed to the failure stress. The calculation was based on the equivalent inclusion method proposed by Eshelby and on an assumption of a perfect bond between the matrix and the fibres. The result was found to be consistent with the mechanism of the fracture, the occurrence of the interfacial cracking in the initial stage and the matrix cracking in the final one.

Reinforcing Mechanism by Small Diameter Fiber in Short Fiber Composite

Influence of fiber diameter on the mechanical properties of short fiber composite was studied by using smaller diameter fibers than conventional ones. Strength and toughness of the composite reinforced with the small diameter fibers were improved, compared to those of the composite reinforced with the conventional ones, except for extremely small diameter fibers. Thus, there exists the maximum value for the strength and toughness for the optimum fiber diameter. This result indicates that there is an optimum condition for the reinforcing effectiveness by the small diameter fibers. In order to analyze the reinforc ing mechanism by the small diameter fibers, fracture mechanism of the composite was studied by an acoustic emission analysis, in-situ SEM observation of failure process, and observation of plastic deformation of the matrix. As a result, initiation and propagation of microcracks occurring at fiber/matrix interface were found to be strongly suppressed by using the small diameter fibers, compared with those in the conventional composite. A model for explaining the reinforcing mechanism by the small diameter fibers was pro posed, which can well explain the presence of the optimum fiber diameter, resulting in the highest reinforcing effectiveness for the composite.

Effect of ion implantation on fracture stress of Al2O3

Abstract Effects of ion implantation and subsequent thermal annealing on the fracture stress of single-crystalline α-Al2O3 have been investigated for 400 keV N and 300 keV Ni ions. Upon N or Ni implantation, the flexural strength of a specimen 7 × 25 × 1 mm3 in size increased by 20 to 60% in the ion dose range from 1 × 1015 to 1 × 1017 ions cm 2 . By post-implantation thermal annealing, the relative flexural strength for the N implanted specimen recovered gradually with annealing temperature followed by a complete recovery at around 1300°C. This behavior of recovery for flexural strength has been found to be similar to that for radiation damage. On the other hand no recovery of flexural strength has been observed for the Ni implanted specimen, in which a spinel compound NiAl2O4 formed upon thermal annealing at temperatures above 1000°C. In N implantation, the strengthening results entirely from the effect of radiation damage, whereas in Ni implantation the formation of a surface NiAl2O4 layer with post-implantation thermal annealing is also effective in the strengthening.

Thermal expansion of hot-pressed cordierite glass ceramics

Mesure du coefficient de dilatation thermique de plusieurs echantillons de vitroceramique de cordierite pressee a chaud. Le large spectre de valeurs est relie aux microfissures qui apparaissent au cours du refroidissement et a la transformation de phase hexagonale→orthorhombique