| 1. |
- Zhang, L, et al.
(författare)
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Effects of molecular weight of nitrocellulose on structure and properties of polyurethane nitrocellulose IPNs
- 1999
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Ingår i: Journal of Polymer Science Part B-Polymer Physics. ; 37:14, s. 1623-1631
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Tidskriftsartikel (refereegranskat)abstract
- Semi-interpenetrating polymer network (semi-IPN) coatings were prepared by using castor oil-based polyurethane (PU) and nitrocellulose (NC) with various viscosity-average molecular weights (Mη) from 6 × 104 to 42 × 104, and coated on a regenerated cellulose (RC) film to obtain water-resistant film. The PU/NC coatings and coated films, which were cured at 80°C for 5 min and 2 min, respectively, were investigated by infrared (IR) and ultraviolet (UV) spectroscopy, X-ray diffraction, swelling test, strength test, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The results show that the crosslink densities of the PU/NC semi-IPNs were smaller than that of pure PU, and decreased with the decrease of Mη of nitrocellulose (NC Mη), indicating NC molecules cohered intimately with PU, and hindered the PU network formation. The physical and mechanical properties of the films coated with PU/NC coatings were significantly improved. With the increase of NC Mη, the strength and thermal stability of the coated films increased, but the pliability, water resistivity, and optical transmission decreased slowly. The PU/NC coating with low NC Mη more readily penetrated into the RC film, and reacted with cellulose, resulting in a strong interfacial bonding and dense surface caused by intimate blend of PU/NC in the coated films.
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| 2. |
- Zhang, L, et al.
(författare)
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Water-resistant film from polyurethane/nitrocellulose coating to regenerated cellulose
- 1997
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 36:7, s. 2651-2656
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Tidskriftsartikel (refereegranskat)abstract
- Water-resistant films were obtained from polyurethane (PU)/nitrocellulose coating to regenerated cellulose films, which were prepared by coagulating cellulose cuoxam solution. The PU/nitrocellulose coating layer was cured at 80 degrees C for 2 min and formed semi-interpenetrating polymer networks (semi-IPNs) structure. The tensile strength (sigma(b)), water resistivity (R), water vapor permeability (P), and light transmittance of the coated films changed with nitrocellulose content in the coating, and the best values (such as sigma(b), 679 kg.cm(-2); R, 53%; P, 0.004 g.cm(-2).day(-1)) were attained at 33 wt % nitrocellulose. The TEM, EPMA, DTA, IRI and UV results-showed that the coated films have strong interfacial bonding, which is caused by covalent and hydrogen bonds between the cellulose film and the semi-IPNs coating. The biodegradation half-life t(1/2) of the coated films in soil at 20-30 degrees C was given to be 58 days, and after about 6 months the coated films were almost completely decomposed by microorganisms. SEM and the kinetics of decay studied on the biodegradability were discussed. The water-resistant films coated with PU/nitrocellulose have promising application where biodegradation is important.
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| 7. |
- Grenestedt, Joakim L, et al.
(författare)
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On cracks emanating from wedges in expanded PVC foam
- 1996
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Ingår i: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 54:4, s. 445-456
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Tidskriftsartikel (refereegranskat)abstract
- An experimental and analytical study was made on the effect of stress singularities on the strength of expanded PVC foam materials of different densities. Experiments were performed on specimens with different wedge geometries ranging from sharp cracks, with the ordinary inverted square root stress singularity, to shallow re-entrant corners with weak singularities. A brittle fracture criterion based on a generalised stress intensity factor, called Q, at the wedge tip was fit to experimental data. The critical stress intensity factor, Qcr, for crack initiation depends on the wedge geometry. This dependence was estimated from simple point-stress criteria and a criterion due to Seweryn [Brittle fracture criterion for structures with sharp notches. Engng Fracture Mech. 47, 673-681 (1994)], and good agreement with experimental data was obtained. When the point-stress criterion was applied to Mode II sharp cracks, poor agreement with published data was found. A critical study of the Mode II crack specimen was therefore initiated, leading to the conclusion that the commonly used specimen gives erroneous values of KIIc and the reason seems to be due to crack surface friction. A new Mode II crack specimen which eliminates crack surface friction was proposed and tested, and good agreement with the point-stress criterion was obtained. A criterion for homogeneous materials proved to be adequate also for the porous PVC foams.
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| 8. |
- Hallström, Stefan, 1968-, et al.
(författare)
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Mixed mode fracture of cracks and wedge shaped notches in expanded PVC foam
- 1998
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Ingår i: International Journal of Fracture. - 0376-9429 .- 1573-2673. ; 88:4, s. 343-358
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Tidskriftsartikel (refereegranskat)abstract
- Fracture initiated from a sharp crack or wedge shaped notch in a homogeneous material, subjected to different loading is considered. Singularities in the stress fields at edges and vertices are discussed. A point-stress criterion is used to predict fracture for sharp cracks as well as 90° wedge notches in expanded PVC foam. The point-stress criterion is formulated in a manner allowing failure predictions in general 3D stress situations. The influence of non-singular T-stress at cracks is discussed and substantiated by experimental results.
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| 15. |
- Austrell, Per Erik, et al.
(författare)
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Survey of Design Methods and Material Characteristics in Rubber Engineering
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The unique properties of elastomeric materials are taken advantage of in many engineering applications. Elastomeric units are used as couplings or mountings between stiff structures. Examples of these are shock absorbers, vibration insulators, flexible joints, seals and suspensions.The development of computers and of analysis programs in this area has given engineers a new tool for the design of elastomeric components. Computer simulation by finite element analysis has become increasingly important, allowing the mechanical behavior of products with for complex geometries, as well as loading cases of different kinds to be evaluated. Computer simulations enable both static and dynamic aspects to be analyzed. These matters have been recognized by the manufacturers of rubber products and by their customers. The benefits are shorter time for product development and also quality improvements.However, the possibilities available for finding less complicated technical solutions at lower cost with the use of elastomers, has not been fully utilized. Rubber components could be employed more frequently in design if engineers were more familiar with materials of this sort.Part of the problem lies in education and in the dissemination of information. Engineers working in the design area tend to not be very familiar with elastomeric materials and their properties. The offerings of courses on the mechanics of polymers at schools and universities are very limited. Skillful engineers in this field have usually acquired their knowledge through many years of experience and not formal education.Moreover, the complicated nature of the material behavior involved makes it difficult to devise general design rules and design tools. Only recently have computers and analysis programs become powerful enough for the analysis of nonlinear elastic problems involving large strains.It is essential, if one is to become competitive in high-tech applications, to possess a thorough knowledge of computer methods, material models and test methods available.There has likewise been a lack of relevant data for the computer analysis of elastomeric materials. The design tools employed rely on the material models available and on the test data required for the calibration of these models. In many cases, the only information available for analysis is a value for the hardness of the rubber in question. The wide variety of rubber compounds is also a problem. The characterization of different materials is costly and time-consuming. There is thus a need for simple and reliable methods to characterize the different vulcanizates.
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