| 1. |
- Liu, X. H., et al.
(författare)
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High-temperature X-ray diffraction studies on polyamide6/clay nanocomposites upon annealing
- 2002
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Ingår i: Polymer Bulletin. - : Springer Science and Business Media LLC. - 0170-0839 .- 1436-2449. ; 48:05-apr, s. 381-387
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Tidskriftsartikel (refereegranskat)abstract
- The influence of nanodispersed clay on the alpha crystalline structure of polyamide 6 (PA6) was examined in-situ with X-ray diffraction (XRD) between room temperature and melting. In pure PA6 upon annealing the alpha crystalline phase was substituted by an unstable pseudohexagonal phase at 150degreesC, then it transformed into a new stable crystalline structure - high temperature alpha' phase above the transition temperature. However, in PA6/clay nanocomposite (PA6CN), the alpha phase did not present crystalline phase transition on heating. The increase in the annealing temperature only led to continuous intensity variation. The different behaviors were caused by the confined spaces formed by silicate layers, which constrained the mobility of the polymer chains in-between.
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| 2. |
- Liu, X. H., et al.
(författare)
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Investigation on unusual crystallization behavior in polyamide 6/montmorillonite nanocomposites
- 2002
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Ingår i: Macromolecular materials and engineering. - 1438-7492 .- 1439-2054. ; 287:8, s. 515-522
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Tidskriftsartikel (refereegranskat)abstract
- The crystallization behavior and crystal structure of polyamide 6/montmorillonite (PA6/MMT) nanocomposites were investigated by differential scanning calorimetry and X-ray diffraction, and an interesting behavior was observed. The material was prepared via melt compounding using an organophilic clay obtained by co-intercalation of epoxy resin and quaternary ammonium into Na-montmorillonite. A maximum in degree of crystallinity was obtained at 5 wt.-% MMT and the reasons for this, based on the MMT layer distribution, were discussed. The degree of crystallinity showed a strong dependence on the cooling rates. In contrast with typical behavior, a higher cooling rate resulted in a higher degree of crystallinity. In nanocomposites, the gamma-crystalline phase was dominant.
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| 3. |
- Liu, X. H., et al.
(författare)
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Polyamide 6/clay nanocomposites using a cointercalation organophilic clay via melt compounding
- 2003
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 88:4, s. 953-958
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Tidskriftsartikel (refereegranskat)abstract
- Polyamide 6/clay nanocomposites (PA6CN) were prepared via the melt compounding method by using a new kind of organophilic clay, which was obtained through cointercalation of epoxy resin and quaternary ammonium into Na-montmorillonite. The dispersion effect of this kind of organophilic clay in the matrix was studied by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM); the silicate layers were dispersed homogeneously and nearly exfoliated in the matrix. This was probably the result of the strong interaction between epoxy groups and amide end groups of PA6. The mechanical properties and heat distortion temperature (HDT) of PA6CN increased dramatically. The notched Izod impact strength of PA6CN was 80% higher than that of PA6 when the clay loading was 5 wt%. Even at 10 wt% clay content, the impact strength was still higher than that of PA6. The finely dispersed silicate layers and the strong interaction between silicate layers and matrix decreased the water absorption. At 10 wt% clay content, PA6CN only absorbs half the amount of water compared with PA6. The dynamic mechanical properties of PA6CN were also studied.
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| 4. |
- Liu, X. H., et al.
(författare)
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Polyamide 6-clay nanocompositles/polypropylene-grafted-maleic anhydride alloys
- 2001
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 42:19, s. 8235-8239
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Tidskriftsartikel (refereegranskat)abstract
- Polyamide 6-clay nanocomposites (PA6CN) based on montmorillonite typically show some brittleness with clay addition. In order to address this problem, PA6CN/PP-g-MAH alloys were prepared through blending PA6CN with polypropylene-grafted-maleic anhydride (PP-g-MAH). The mechanical properties, dynamic mechanical temperature spectra, morphology and water absorption of the alloys were studied. Compared with PA6CN, the notched impact strength of the alloys increased greatly while the alloys still maintained higher stiffness and strength than that of PA 6. The morphological studies via scanning electron microscopy (SEM) showed a PP-g-MAH toughen phase dispersed in PA6CN matrix. As the PP-g-MAH content was increased, reduced water absorption was observed.
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| 5. |
- Liu, X. H., et al.
(författare)
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Polymorphism in polyamide 66/clay nanocomposites
- 2002
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:18, s. 4967-4972
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Tidskriftsartikel (refereegranskat)abstract
- Polyamide 66/clay nanocomposites (PA66CN) were prepared via melt compounding method by using a new kind of organophilic clay, which was obtained through co-intercalation of epoxy resin and quaternary ammonium into Na-montmorillorlite. The silicate layers were dispersed homogeneously and nearly exfoliated in polyamide 66 (PA66) matrix. The introduction of silicate layers induced the appearance of the gamma phase in PA66CN at room temperature, more clay loadings would amplify this phenomenon; the addition of clay also changed the structure of the a crystalline phase. The presence of silicate layers increased the crystallization rate and had a strong hetero phase nucleation effect on PA66 matrix. The lower Brill transition temperature of PA66CN can be attributed to the strong interaction between polyamide chains and surfaces of silicate layers.
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| 6. |
- Neikter, Magnus, 1988-, et al.
(författare)
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Microstructural characterization of binary microstructure pattern in selective laser-melted Ti-6Al-4V
- 2019
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer. - 0268-3768 .- 1433-3015. ; 104:1-4, s. 1381-1391
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Tidskriftsartikel (refereegranskat)abstract
- Selective laser melting (SLM) is an additive manufacturing process that offers efficient manufacturing of complex parts with good mechanical properties. For SLM, process parameters and post-processing are of importance as they affect the microstructure and consequently the mechanical properties. A feature in the microstructure, which is formed in SLM due to the fast cooling rate, is a binary microstructure pattern (BMP). The BMP is found in the horizontal plane and is formed with various laser scan angles between adjacent layers. The easiest distinguishable strategy is 90°, which renders a shape similar to a chessboard. In this work, the BMP phenomenon was investigated in detail and a microstructural characterization was performed on the fine microstructure zone (FMZ) that separates the coarse microstructure zones (CMZ), by using light optical and scanning electron microscopes (SEM) that were equipped with electron backscattered (EBSD) and energy dispersive x-ray spectroscopy (EDS) detectors. Moreover, the effect of the process parameter hatch distance on the BMP was investigated and the overlapping between neighboring scan tracks in SLM was found to influence the size of the BMP, while the thickness of the FMZ remained constant. Different post-SLM heat treatments were performed and it was shown that the BMP retained unless the heat treatment temperature reached above the β transus temperature. EBSD and β grain reconstruction were performed as well to reveal the columnar β grain orientations. The result showed that each CMZ and FMZ originates from a respective parent β grains.
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| 7. |
- Wu, Q. J., et al.
(författare)
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An unusual crystallization behavior in polyamide 6/montmorillonite nanocomposites
- 2001
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Ingår i: Macromolecular rapid communications. - 1022-1336 .- 1521-3927. ; 22:17, s. 1438-1440
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Tidskriftsartikel (refereegranskat)abstract
- The crystallization behavior and structure of polyamide 6 (PA6) nanocomposites containing 3 wt.-% montmorillonite (MMT) were investigated for different cooling conditions using differential scanning calorimetry and X-ray diffraction. In sharp contrast to PA6 and other semicrystalline polymers, increased cooling rates resulted in higher crystallinity of PA6/MMT. The. highest crystallinity (60.8%) occurred in the liquid nitrogen-quenched PA6/MMT film. The results show that the gamma -crystalline form is dominant in the rapidly cooled PA6/MMT.
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| 8. |
- Wu, Q. J., et al.
(författare)
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FT-IR spectroscopic study of hydrogen bonding in PA6/clay nanocomposites
- 2002
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:8, s. 2445-2449
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Tidskriftsartikel (refereegranskat)abstract
- Fourier transform infrared spectroscopy was used to investigate PA6/clay nanocomposites (PA6CN) with various cooling histories from the melt, including rapid cooling (water-quenched), middle-rate cooling (air-cooling) and slow cooling (mold-cooling). In contrast to pure PA6 dominated by the alpha-phase, the addition of clay silicate layers favor the formation of the gamma-crystalline phase in PA6CN. We focus on the reason why silicate layers favor the formation of gamma-phase in PA6. Vaia et al. suggested that the addition of clay layers forces the amide groups of PA6 out of the plane formed by the chains. This results in conformational changes of the chains, which limits the formation of H-bonded sheets so that the gamma-phase is favored. If this assumption is correct, PA6CN is expected to show some differences as compared with PA6 with respect to hydrogen bonding. The silicate layers were indeed found to weaken the hydrogen bonding both in the alpha- and gamma-phases This was also confirmed by X-ray diffraction studies. The gamma-phase is most likely concentrated in regions close to the silicate layers, whereas the alpha-phase is favored in the bulk matrix.
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