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.
Highlights
Elastomers are polymers that can typically undergo chemical reactions after being heated to form bonds or crosslinks between the polymer chains, forming a flexible polymer network [1]
The remaining 62 articles were relevant to the question of how layered double hydroxides (LDHs) can be used to affect the mechanical properties of elastomers, and these are discussed in detail
Laskowska et al [64] found that the Mg content, aspect ratio and surface area of the LDH have an effect on the properties of XNBR
Summary
Elastomers are polymers that can typically undergo chemical reactions after being heated to form bonds or crosslinks between the polymer chains, forming a flexible polymer network [1]. For use in many of these applications, elastomers need to be reinforced to enhance their mechanical properties. In recent years other reinforcing fillers, such as montmorillonite (MMT) and layered double hydroxides (LDHs) have been attracting attention. Both LDH and MMT are layered clays. MMT is a cationic silicate clay that consists of thin layers of tetrahedral silica sheets sandwiching an octahedral alumina sheet [4] Layered silicates such as montmorillonite have long been used as fillers in polymers [5,6]. More research has been conducted on LDH in elastomers since the previous review was published This systematic literature review focuses on how LDH various types of LDH have been used to affect the mechanical properties of elastomers.
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