MMT clay was organically modified to prepare polymer nanocomposites with
melamine phosphate by a cation exchange process in water; the organic compound
was intercalated with MMT clay platelets and resulted in an increased d-spacing, as
shown in Fig. 7.7. During polymer combustion, the non-combustible gases
evolving from the decomposition of blowing agent MA-MMT/MPP contribute to
the IFR activity and anti-dripping properties. Some photographs of the tested
specimens are shown in Fig. 7.7; it can be clearly seen that in the presence of
MA-MMT and MPP, excellent intumescent char formation occurred and it resulted
in a strong anti-dripping characteristic compared to other composites due to the
high melt viscosity of the polymer in the presence of MMT clay [76, 77]. PA6-3
(MA-MMT/MPP:1/24) showed the highest LOI value and achieved a V-0 rating in
the UL-94 test, whereas PA6-6 (MA-MMT/MPP:5/20) showed a low LOI value
and no rating in the UL-94 test. The reason behind this observation is not clearly
known but it may be assumed that at particular compositions of MA-MMT/MPP,
there occurs a strong synergetic reaction between the clay and MPP; furthermore,
the PA6-3 system contained a higher quantity of phosphorus than the PA6-6 system. Phosphorus can move to the surface along with the MMT clay and enrich and
strengthen the char layer [78]. Shan et al. [79] prepared TPU nanocomposites using
combinations of an IFR (APP + PER) and NaNiP and studied the importance of
composition and PER in determining the FR activity. They noticed that TPU
nanocomposite systems containing TPU3 (APP + PER/NaNiP: 19/1) showed a V-0
rating in the UL-94 test, high LOI value of 32%. With increasing NaNiP content in
TPU5 (APP + PER/NaNiP: 15/5), the LOI value decreased and the composite
achieved a V-2 rating in the UL-94 test. Literature clearly indicates that the synergetic effect and phosphorus content play important roles in such cases. At particular compositions, one can observe a strong synergetic effect and the presence of
NaNiP induces dense intumescent char formation, thus leading to strong IFR
activity. A variety of P,N-based compounds and metal oxides have been used for
clay surface modification to prepare polymer nanocomposites with different IFRs
(Table 7.2). It is clear that the FR activity significantly improved with a combination of IFRs at specific compositions. In some cases, increasing the modified clay
content decreased the IFR activity because there was no synergetic effect. In
addition, phosphorus content also influences the IFR activity (Fig. 7.7).
7.3 Graphene-Based FR PNCs
Graphene has a layered structure and the carbon atoms are arranged in monolayers
similar to a honeycomb network structure; graphene has a large surface area and
strong absorption capacity. Owing to its structural features, graphene exhibits high
thermal stability, mechanical strength, strong barrier properties, and toxic gas
absorption capacity. GO exhibits good compatibility and strong interactions with
polymers and can be used to form 3D polymer network structures. Hence, graphene
has attracted the attention of polymer chemists to prepare polymer nanocomposites
96
7 Polymer Nanocomposites for Fire Retardant Applications
melamine phosphate by a cation exchange process in water; the organic compound
was intercalated with MMT clay platelets and resulted in an increased d-spacing, as
shown in Fig. 7.7. During polymer combustion, the non-combustible gases
evolving from the decomposition of blowing agent MA-MMT/MPP contribute to
the IFR activity and anti-dripping properties. Some photographs of the tested
specimens are shown in Fig. 7.7; it can be clearly seen that in the presence of
MA-MMT and MPP, excellent intumescent char formation occurred and it resulted
in a strong anti-dripping characteristic compared to other composites due to the
high melt viscosity of the polymer in the presence of MMT clay [76, 77]. PA6-3
(MA-MMT/MPP:1/24) showed the highest LOI value and achieved a V-0 rating in
the UL-94 test, whereas PA6-6 (MA-MMT/MPP:5/20) showed a low LOI value
and no rating in the UL-94 test. The reason behind this observation is not clearly
known but it may be assumed that at particular compositions of MA-MMT/MPP,
there occurs a strong synergetic reaction between the clay and MPP; furthermore,
the PA6-3 system contained a higher quantity of phosphorus than the PA6-6 system. Phosphorus can move to the surface along with the MMT clay and enrich and
strengthen the char layer [78]. Shan et al. [79] prepared TPU nanocomposites using
combinations of an IFR (APP + PER) and NaNiP and studied the importance of
composition and PER in determining the FR activity. They noticed that TPU
nanocomposite systems containing TPU3 (APP + PER/NaNiP: 19/1) showed a V-0
rating in the UL-94 test, high LOI value of 32%. With increasing NaNiP content in
TPU5 (APP + PER/NaNiP: 15/5), the LOI value decreased and the composite
achieved a V-2 rating in the UL-94 test. Literature clearly indicates that the synergetic effect and phosphorus content play important roles in such cases. At particular compositions, one can observe a strong synergetic effect and the presence of
NaNiP induces dense intumescent char formation, thus leading to strong IFR
activity. A variety of P,N-based compounds and metal oxides have been used for
clay surface modification to prepare polymer nanocomposites with different IFRs
(Table 7.2). It is clear that the FR activity significantly improved with a combination of IFRs at specific compositions. In some cases, increasing the modified clay
content decreased the IFR activity because there was no synergetic effect. In
addition, phosphorus content also influences the IFR activity (Fig. 7.7).
7.3 Graphene-Based FR PNCs
Graphene has a layered structure and the carbon atoms are arranged in monolayers
similar to a honeycomb network structure; graphene has a large surface area and
strong absorption capacity. Owing to its structural features, graphene exhibits high
thermal stability, mechanical strength, strong barrier properties, and toxic gas
absorption capacity. GO exhibits good compatibility and strong interactions with
polymers and can be used to form 3D polymer network structures. Hence, graphene
has attracted the attention of polymer chemists to prepare polymer nanocomposites
96
7 Polymer Nanocomposites for Fire Retardant Applications