ساختار پلیمری فوق روان کنندگان
Abstract
1-Introduction
2-Research significance
3-Materials
4-Experimental methods
5-Results and discussion
6-Interpretation of the intercalation mechanism of PCE side chains
7-Conclusions
Declaration of Competing Interest
Acknowledgments
References
Abstract
The influence of polymeric structure of polycarboxylate-ether (PCE) based superplasticizers on the intercalation behavior in sodium montmorillonite clay (Na-MNT) is investigated by performing in-situ X-ray diffraction (XRPD) on fresh, unaltered clay pastes. The use of this technique reveals the real influence of the PCE structure and of the PCE/clay dosage ratio on the expansion profile of the clay. This is not observed with the traditional XRPD methodology performed on dried clay pastes, which shows the same values of d-spacing despite using polymers of diverse structures. It is observed that PCE polymers with long side chains and high side chain density result in larger expansion. Additionally, polymers with a high anionic charge saturate the interlaminar space of montmorillonite at a lower dosage. The experimental results also indicate that clay exfoliation is critical in the intercalation process and the exfoliation tendency of the clay is influenced by the structure of PCE polymers.
Introduction
The dispersing capacity and water reduction efficiency of polycarboxylate-ether (PCE) based superplasticizers is severally affected by the presence of montmorillonite clays (MNT) in the sands used for concrete production. This type of clays has the ability to absorb large quantities of PCE polymers through an intercalation mechanism of the PEG/PEO (poly-ethylene glycol/polyethylene oxide) side chains of the polymer [1,2], which is responsible for the partial or total loss of their dispersing capacity. The absorption behaviour of PCE-based superplasticizers on MNT clay has already been investigated by different authors using XRPD analysis on centrifuged and dried clay pastes [1,2]. These studies show almost no influence on the d-spacing of MNT clay when different structures of PCE polymers are used since the maximum clay expansion value always remains in the range of 18–۲۱ Å and, in all cases, the average differences of d001 values within PCE polymers of diverse structures does not exceed 3 Å (the distance equivalent to one water molecule arranged in the interlayer of MNT clays).