On programming of polyvinylidene fluoride–limestone composite for four-dimensional printing applications in heritage structures

Heritage structures are under the effect of chemical, physical and biological weathering, and out of these common effects, chemical weathering has a significant impact (as it results in nifty formation and causes fractures in heritage structures). Chemical weathering may include carbonation, oxidation, hydration, hydrolysis, and acidification. Most heritage structures are made up of limestone, which is more susceptible to carbonation. According to the reported literature, commercial practices for the maintenance and repair of these heritage structures use epoxy-based solutions, which may not be best suited as per the various regulations imposed by different government/public authorities. But so far little has been reported on the use of innovative, programmable thermoplastic composites for the maintenance and repair of such structures. This study highlights the effect of chemical treatment (as a stimulus) using a one-way programming of three-dimensional-printed thermoplastic composite-based (polyvinylidene fluoride–6% limestone) functional prototype as a solution for the maintenance and repair of heritage structures (grade III). For one-way programming, three-dimensional-printed substrate is exposed to dimethylformamide, and the changes in morphological and surface properties are noticed. After this, carbonation cycle (with carbonic acid) is performed and the changes in morphological and surface properties are compared to ascertain the stimulus effect for one-way programming (of polyvinylidene fluoride–6% limestone composite). The results of the study outline that the prepared composite may be programmed by controlling the exposure of dimethylformamide and carbonic acid (as a stimulus). Further best settings for preparing feedstock filament (for three-dimensional printing of functional prototypes in case of a selected heritage structure) are 200 °C screw temperature, 0.35 N m torque and an applied load of 8 kg in terms of better mechanical properties and shore D hardness.