55
properties of the composites still remains the object of research studies (Hernández
et al., 2017).
Another approach to increase the polarity of the GTR surface is chlorination,
which is usually performed by using of trichloroisocyanuric acid (TCl) (Naskar
et al. 2001, 2002). TCl as in the case of other acids, allows controlled oxidation of
the GTR surface resulting in the formation of new functional groups, such as C=O
and S=O. Recently, Yao et al. (2019) indicated that chlorination of GTR resulted in
a reduction in particles size (particle size >0.85 mm = 96.8 wt.% for untreated GTR
and 56.3–83.1 wt.% for GTR after chlorination (as a function of the degree of chlorination)) and also a significant improvement in the tensile properties of its revulcanized. Tensile strength and elongation at break for the untreated GTR was 2.4 MPa
and 143%, respectively, while for the GTR after chlorination these parameters were
in the range of: 5.1–10.3 MPa and 72–94%.
The creation of polar groups is also possible with other oxidizing agents. In line
with this, Sonnier et al. (2006, 2007) tested several oxidation treatments on HDPE/
GTR mixtures: using a wet process with potassium permanganate (KMnO 4 ) and a
dry process using γ-irradiation. The modified GTR powder was combined in a polypropylene composite matrix containing grafted maleic anhydride. The results with
KMnO 4 showed an improvement in the elongation at break, which was related to the
better compatibility between the dispersed GTR particles and the matrix. These
authors also used γ-irradiation to induce scission of the polymer chains, which
allows the creation of the free radicals suitable for crosslinking or reaction with
oxygen from the air, resulting in the formulation of polar groups. GTR oxidation
was also tested by Sonnier et al. (2006, 2007) through specific tests, however, the
mechanical properties of the materials studied were not significantly improved.
Some other alternatives for the creation of polar groups on the GTR surface can
be conducted through the use of ozone (Cao et al. 2014), high energy radiation,
corona discharge, electro-beam or plasma to create oxidized groups (Ratnam et al.
2013; Xiang et al. 2018). The results obtained by these treatments have been adequate to improve compatibility with polar polymers. The main drawback of these
methods seems to be their viability from an economic perspective.
4.3.3 Using Coupling Agents and Additives
The use of coupling agents is a common practice in composite materials. The coupling agents act as a link between the reinforcement and the filler, in this case, the
GTR and the matrix. The coupling agent must have an affinity for both components
and the ability to successfully improve compatibility between them. The application
of compatibilizers is easy and does not require special equipment to produce the
composite. Under these assumptions, the use of coupling agents or additives could
lead to a process that would be environmentally friendly, economically competitive
and suitable for industrial scale application.
4 Reactive Processing and Functionalization of Ground Tire Rubber
properties of the composites still remains the object of research studies (Hernández
et al., 2017).
Another approach to increase the polarity of the GTR surface is chlorination,
which is usually performed by using of trichloroisocyanuric acid (TCl) (Naskar
et al. 2001, 2002). TCl as in the case of other acids, allows controlled oxidation of
the GTR surface resulting in the formation of new functional groups, such as C=O
and S=O. Recently, Yao et al. (2019) indicated that chlorination of GTR resulted in
a reduction in particles size (particle size >0.85 mm = 96.8 wt.% for untreated GTR
and 56.3–83.1 wt.% for GTR after chlorination (as a function of the degree of chlorination)) and also a significant improvement in the tensile properties of its revulcanized. Tensile strength and elongation at break for the untreated GTR was 2.4 MPa
and 143%, respectively, while for the GTR after chlorination these parameters were
in the range of: 5.1–10.3 MPa and 72–94%.
The creation of polar groups is also possible with other oxidizing agents. In line
with this, Sonnier et al. (2006, 2007) tested several oxidation treatments on HDPE/
GTR mixtures: using a wet process with potassium permanganate (KMnO 4 ) and a
dry process using γ-irradiation. The modified GTR powder was combined in a polypropylene composite matrix containing grafted maleic anhydride. The results with
KMnO 4 showed an improvement in the elongation at break, which was related to the
better compatibility between the dispersed GTR particles and the matrix. These
authors also used γ-irradiation to induce scission of the polymer chains, which
allows the creation of the free radicals suitable for crosslinking or reaction with
oxygen from the air, resulting in the formulation of polar groups. GTR oxidation
was also tested by Sonnier et al. (2006, 2007) through specific tests, however, the
mechanical properties of the materials studied were not significantly improved.
Some other alternatives for the creation of polar groups on the GTR surface can
be conducted through the use of ozone (Cao et al. 2014), high energy radiation,
corona discharge, electro-beam or plasma to create oxidized groups (Ratnam et al.
2013; Xiang et al. 2018). The results obtained by these treatments have been adequate to improve compatibility with polar polymers. The main drawback of these
methods seems to be their viability from an economic perspective.
4.3.3 Using Coupling Agents and Additives
The use of coupling agents is a common practice in composite materials. The coupling agents act as a link between the reinforcement and the filler, in this case, the
GTR and the matrix. The coupling agent must have an affinity for both components
and the ability to successfully improve compatibility between them. The application
of compatibilizers is easy and does not require special equipment to produce the
composite. Under these assumptions, the use of coupling agents or additives could
lead to a process that would be environmentally friendly, economically competitive
and suitable for industrial scale application.
4 Reactive Processing and Functionalization of Ground Tire Rubber