Abstract:
Layered double hydroxides (LDHs) have attracted interest as reinforcing fillers in elastomers
due to their ease of synthesis and customisability. A systematic review was performed on
the effect of LDHs on the mechanical properties of elastomers using the Scopus database. Of the 61
articles relevant to the search criteria, the majority were published on polyurethane (PU) and nitrile
butadiene rubber (NBR). Mg-Al LDH was used in most of the studies and Zn-Al LDH was used
second most common. LDH can act as a reinforcing filler, typically increasing tensile strength even at
low concentrations, so it could be used as an alternative to traditional reinforcing fillers for elastomers.
LDH can also be made a functional filler by selecting the right metals and interlayer anions. It was
found that Mg-Al LDH and Zn-Al LDH can both participate in crosslinking reactions and can replace
MgO and ZnO, respectively. Less Zn ions are required for crosslinking when LDH is used than when
ZnO is used, making LDH more environmentally friendly. Organic modification is usually required
to improve compatibility with the elastomer matrix, especially in non-polar elastomers. It enables
exfoliation of the LDH and intercalation of polymer chains into the LDH interlayer to occur. Organic
modifiers can also be used to functionalise the LDH. Stearic acid used in crosslinking systems can be
replaced by stearate anions from stearate-modified LDH.
