A siloxane‐grafted new diamino monomer DBPDMS has been prepared and used as a co‐monomer in combination with the fluorinated diamine monomer TFBB to prepare siloxane‐grafted polyimides. The polymers have been characterized by means of GPC, IR, and NMR. Their thermal, mechanical, and surface properties have been evaluated and compared with the homopolyimide and with polyimides where polysiloxane is incorporated in the main chain. DSC revealed melting of the grafted siloxane chain at sub‐ambient temperature and a glass transition corresponding to the main polymer chain at high temperature. Isothermal gravimetric analysis at 350 °C indicated that grafted siloxane moiety can be removed thermally from the polymer chain without affecting the polymer backbone.
Three series of composite films based on polyimide and MWNTs were prepared by conversion of pyromellitic dianhydride and 4,4′‐oxydianiline in the presence of the nanotubes, followed by thermal imidization. Carboxy‐ and amino‐functionalized as well as unmodified nanotubes were used. It was demonstrated that just 0.5 wt.‐% of nanotubes increased the tensile properties of the composite films distinctly. Surprisingly, a significant influence of the functional groups on the mechanical performance of the composite films could not be demonstrated. However, it was shown that functional groups may reduce the conductivity of the films. Furthermore, the influence of ultrasonication is discussed.
Commercial Udel® poly(ether sulfone) (PSU) was filled with three different commercially available multiwalled carbon nanotubes (MWCNTs) by small scale melt mixing. The MWCNTs were as grown NC 7000 and two of its derivatives prepared by ball milling treatment. One of them was unmodified (NC 3150); the other was amino modified (NC 3152). The main difference beside the reactivity was the reduced aspect ratio of NC 3150 and NC 3152 caused by ball milling process. All PSU/MWCNT composites with similar filler content were prepared under fixed processing conditions and comparative analysis of their electrical and mechanical properties were performed and were correlated with their microstructure, characterized by optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A non-uniform MWCNT dispersion was observed in all composites. The MWCNTs were present in form of agglomerates in the size of 10–60 μm whereas the deagglomerated part was homogeneously distributed in the PSU matrix. The differences in the agglomeration states correlate with the variations of properties between different PSU/MWCNT composites. The lowest electrical percolation threshold of 0.25–0.5 wt.% was observed for the shortened non-functionalized MWCNT composites and the highest for amine-modified MWCNT composites (ca. 1.5 wt.%). The tensile behavior of the three composites was only slightly altered with CNT loading as compared to the pure PSU. However, the elongation at break showed a reduction with MWCNT loading and the reduction was least for composite with best MWCNT dispersion. 相似文献
Product-mix of castings of different types/sizes can be produced in a heat (batch of melt) if all these castings require similar raw material composition. However, inappropriate product-mix may lead to under utilization of furnace capacity or failure in timely delivery or overproduction of castings or may call for deployment of excess resources for packing of molds to enable starting of the pouring operation in time. Some objectives, again, can be conflicting in nature. This paper presents a weighted integer goal programming model for the product-mix planning, developed in the context of a small scale iron foundry. Implementation of the model is illustrated using real life data from an Indian foundry. 相似文献
