57
4.3.4 Grafting of Chemical Compounds on the Surface of GTR
The increase in interfacial adhesion of the GTR matrix can be achieved by grafting
monomers or other chemical compounds on the surface of GTR. This way differs
essentially from the others presented above. In this case, the modification of the
GTR includes a chemical bonding reaction, grafting the chosen modifier to the
GTR. This grafted component participates in the subsequent crosslinking reaction
or becomes entangled with macromolecular chains of the matrix. Common monomers used for grafting on GTR are: styrene, maleic anhydride, acrylamide and
derivatives from acrylic and metacrylic acids.
The reaction of grafting can be carried out by:
I. Decomposition of a free-radical initiators at high temperatures: has been
applied to graft styrene, maleic anhydride and others compounds on the double
bonds of GTR. They are generally applied in an internal mixer using an initiator
such as dibenzoyl peroxide. The resulting polymer mixtures including maleic
anhydride and styrene grafted GTR have shown improved mechanical performance compared to samples with untreated GTR (Coiai et al. 2006; Zhang
et al. 2012).
II. High energy radiation: maleic anhydride and acrylamide have been grafted by
γ-irradiation onto GTR to develop thermoplastic elastomers (Tolstov et al.
2007). Abdel-Bary et al. (1997) grafted GTR with acrylamide, acrylic acid,
acrylonitrile by this technique.
III. Photo-induced grafting: Fuhrmann and Karger-Kocsis (2003) functionalized
the GTR with glycidyl methacrylate and methacrylic acid, which was subsequently treated by UV irradiation. Allylamine and bismaleimide have been also
grafted onto GTR by this method (Du et al. 2005; Shanmugharaj et al. 2006).
Kocevski et al. (2012) also indicated that grafting of acrylic acid could occur
under mild conditions (temperature: 80–85 °C, nitrogen atmosphere) even without
initiators. The scheme of this reaction is presented in Fig. 4.10. It was found that the
GTR functionalized with acrylic acid produced an increase in the viscosity and
failure temperature of the modified bitumen.
Some researchers also recommend pretreatment of GTR before grafting to activate the surface of GTR and make it more suitable for subsequent modification or
functionalization. Fan and Lu (2011) proposed the ozonization of GTR before the
grafting reaction with methyl methacrylate. The intensity of the ozonization treatment had a beneficial impact on the degree of grafting and, consequently, the efficiency of the modification.
Xiaowei et al. (2017) GTR pretreated with oxygen in the low-temperature
plasma. Subsequently, the pretreated GTR was modified by a low temperature
polymerization process in the presence of ethanol in order to improve the adhesion
property with the oil well cement matrix and the performance properties of cement.
The results showed that the modified GTR had a rougher surface than the pretreated
GTR, and that hydrophilic groups, such as -COOH, C–OH and -CHO, were created
4 Reactive Processing and Functionalization of Ground Tire Rubber
4.3.4 Grafting of Chemical Compounds on the Surface of GTR
The increase in interfacial adhesion of the GTR matrix can be achieved by grafting
monomers or other chemical compounds on the surface of GTR. This way differs
essentially from the others presented above. In this case, the modification of the
GTR includes a chemical bonding reaction, grafting the chosen modifier to the
GTR. This grafted component participates in the subsequent crosslinking reaction
or becomes entangled with macromolecular chains of the matrix. Common monomers used for grafting on GTR are: styrene, maleic anhydride, acrylamide and
derivatives from acrylic and metacrylic acids.
The reaction of grafting can be carried out by:
I. Decomposition of a free-radical initiators at high temperatures: has been
applied to graft styrene, maleic anhydride and others compounds on the double
bonds of GTR. They are generally applied in an internal mixer using an initiator
such as dibenzoyl peroxide. The resulting polymer mixtures including maleic
anhydride and styrene grafted GTR have shown improved mechanical performance compared to samples with untreated GTR (Coiai et al. 2006; Zhang
et al. 2012).
II. High energy radiation: maleic anhydride and acrylamide have been grafted by
γ-irradiation onto GTR to develop thermoplastic elastomers (Tolstov et al.
2007). Abdel-Bary et al. (1997) grafted GTR with acrylamide, acrylic acid,
acrylonitrile by this technique.
III. Photo-induced grafting: Fuhrmann and Karger-Kocsis (2003) functionalized
the GTR with glycidyl methacrylate and methacrylic acid, which was subsequently treated by UV irradiation. Allylamine and bismaleimide have been also
grafted onto GTR by this method (Du et al. 2005; Shanmugharaj et al. 2006).
Kocevski et al. (2012) also indicated that grafting of acrylic acid could occur
under mild conditions (temperature: 80–85 °C, nitrogen atmosphere) even without
initiators. The scheme of this reaction is presented in Fig. 4.10. It was found that the
GTR functionalized with acrylic acid produced an increase in the viscosity and
failure temperature of the modified bitumen.
Some researchers also recommend pretreatment of GTR before grafting to activate the surface of GTR and make it more suitable for subsequent modification or
functionalization. Fan and Lu (2011) proposed the ozonization of GTR before the
grafting reaction with methyl methacrylate. The intensity of the ozonization treatment had a beneficial impact on the degree of grafting and, consequently, the efficiency of the modification.
Xiaowei et al. (2017) GTR pretreated with oxygen in the low-temperature
plasma. Subsequently, the pretreated GTR was modified by a low temperature
polymerization process in the presence of ethanol in order to improve the adhesion
property with the oil well cement matrix and the performance properties of cement.
The results showed that the modified GTR had a rougher surface than the pretreated
GTR, and that hydrophilic groups, such as -COOH, C–OH and -CHO, were created
4 Reactive Processing and Functionalization of Ground Tire Rubber