Cross-linking of poly(vinyl alcohol) chains by Ca ions in macro-defect-free cements

In the macro-defect-free cements (MDFs), a cross-linking of the polymer chains by Al or Ca ions coming from the hydration reactions of the cement paste may have crucial effects on the mechanical properties achieved by the final materials as well as on the material processing. In the present study, the cross-linking of poly(vinyl alcohol) (PVA) chains by Ca ions has been investigated with first-principles theoretical methods and compared with a previously investigated case of cross-linking of poly(acrylic acid) (PAA) chains. The achieved results show the existence of a Ca-PAA cross-linking that is significantly more efficient than that realized in the case of the Ca-PVA system. This result implies that the Ca-O bonds involved in the cross-linking of the PVA and PAA chains are affected by the different functional groups present in the two polymer chains and agrees with the improvement of the mechanical properties observed when the PVA polymer is replaced by the PAA polymer in Portland-cement-based MDFs. The achieved results also indicate that the Ca-polymer interactions may have significant effects on the mechanical properties of the above MDFs as well as on their processing.