Page 28 - Polymer-based Nanocomposites for Energy and Environmental Applications

Introduction of polymer-based nanocomposites 7

Khudyakov et al. [36] represented PU nanocomposites of photopolymerizable
(UV-curable) by blending nanosilica and organically modified clay (organoclay).
Among the application of PUs, even though the solution-based PU is chiefly used
in industries, water-based PU resin has attracted researchers for its environmentally
friendly characteristics and firesafety [37]. Ibrahim et al. [38] synthesized a renewable
resource polymer (castor-oil-based PU) as a host in polymer electrolyte for electro-
chemical devices. In this research, the polyurethane and LiI and NaI were mixed in
different weigh percentage to produce a film of polymer electrolytes.

1.2.3.5 Epoxy matrixes
In 1938, epoxy resin was introduced by Pierre Castan, a chemist in Switzerland, and
consequently, it was first commercialized in 1946. These days, epoxy resins are
widely performed as protective coatings or structural applications (e.g., composites,
casting, and adhesives) [39,40]. Among the thermoset family, the epoxy resin can
exhibit the best characteristics as mechanical properties and environmental resistance
with several advantages. Furthermore, based on their low viscosity, these resins can be
utilized at room temperature to cover the required space. Also, they provide low
shrinkage that leads to low residual stress after cross-linking. In the PNC systems,
epoxy resins are reinforced by employing nanofillers in order to improve the required
properties such as mechanical and chemical. In average, the epoxy resins have more
than one epoxide groups per molecule in their structure. Commercial types of epoxy
resins are cycloaliphatic, aliphatic, or aromatic backbones, which are made from
either epichlorohydrin or direct epoxidation of olefins and peracids. The most
prevalent intermediate for epoxy resins is the diglycidyl ether of bisphenol
A (DGEBA), which is produced from bisphenol A and excess epichlorohydrin as
mentioned in Fig. 1.5.
The epoxy resins need treatment with curing agents or hardeners in order to achieve
three-dimensional infusible and insoluble networks. The curing agents are either
catalytic or coreactive in which the catalytic ones act as initiators for epoxy ring-
opening homopolymerization. There are a wide range of curing agents for epoxy

CH 3
CH 2 CHCH 2 Cl + HO C OH + NaOH
O CH 3
Epichlorohydrin excess Bisphenol A

CH 3 CH 3
CH 2 CHCH 2 O C OCH 2 CHCH 2 O C OCH 2 CHCH 2
O CH 3 OH n CH 3 O
Diglycidyl etherof bisphenol A, DGEBA, n~0.2
Fig. 1.5 Synthesis of diglycidyl ether of bisphenol A (DGEBA) [39,40].