Freeze Drying and Hot Pressing

Figure 3.14. CNT/polymer nanocomposites observed in SEM (a) and (b) P(S-ABu)/MW CNT films surface respectively prepared by evaporation and film formation or freeze-drying and hot-pressing but showing similar fillers distribution (c) and (d) PS matrix containing ungrafted or PS-grafted N-doped CNT a fracture performed at ambient temperature highlights the difference in fillers/matrix interface strength. Scale bars 1 pm.

Fig. 3.27 Scanning electron micrographs of the cryo-fractured surfaces of unvulcanized natural rubber/CW obtained by casting and evaporating (a) and freeze-drying and hot-pressing (b) [39]...

Another method called freeze drying and hot pressing can also be used to prepare nanocomposites but only for unvulcanized NR matrix. In this method, the blends of polymer and chitin whiskers were prepared in water medium to prepare well-dispersed aqueous mixtures, which were then freeze dried to give nanocomposite powders, and the powders were consequently processed into specimen by hot pressing. 

Freeze-drying and hot-pressing of the mixture—or its freeze-drying, extrusion, and hot-pressing—where the dispersion of its nanoparticles in the nanocomposite film strongly depends on the processing technique and conditions. 

A method developed from temperature induced phase separation was completed to obtain PLA/bacterial cellulose composites [174]. In this work, bacterial cellulose was added to 1,4-dioxane and homogenized before PLA was added and dissolved before the mixture was added dropwise into a liquid nitrogen bath. The precipitate was collected and freeze-dried to produce composite microspheres, which were then fed into a twin-screw extruder and were mixed at 180°C, extruded, pelletized and hot press compression moulded into films. PLA films containing bacterial cellulose showed an increase in tensile modulus, with composites containing bacterial cellulose, and chemically modified bacterial cellulose shown to have improvements over PLA alone [174]. 

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