Multi-layer graphene (MLG) particles, visible in TEM images, affecting the mechanical and flame retardant properties of rubber, for instance via increased charring
Source: BAM, Technical Properties of Polymeric Materials division
Rubber is among the most important and widely used polymers, as many of its material properties, like elasticity and resistance to abrasion, find use in a wide array of technical applications. To increase the longevity of synthetic rubbers, carbon black (CB) is added during rubber production, and compounds like aluminum trihydroxide (ATH) endow flame retardancy via the release of water molecules in fire scenarios, thereby reducing the fire hazard.
CB and ATH are economical additives, yet they often require high loadings to attain a high degree of flame retardancy. For every 100 parts rubber, up to 70 parts (= 70 parts per hundred rubber, phr) are CB plus ATH, greatly affecting the mechanical properties of the material.
Nanofillers like graphene are different: they are especially effective fillers for rubber, as small loadings have large impacts on material properties. Several layers of this two-dimensional carbon configuration, called multilayered graphene (MLG), have particular material properties. They are marked by a large surface-to-mass ratio (approx. 250 m2 g-1), determined by the Brunauer-Emmett-Teller (BET) surface. MLG exhibits a multifunctional property in rubbers, as it strengthens the mechanical properties. Moreover, MLG increases the effectivity of ATH and leads to the formation of a thick char layer that functions as a thermal barrier in fires. Due to its multifunctional properties, only small amounts are needed, which is why MLG can significantly reduce the needed CB and ATH amounts.
This paper describes the preparation of composites of polybutadiene and chloroprene (known as Neoprene) containing CB and ATH, and it investigates their mechanical and flame retardant properties. Composites containing varying loadings of MLG, CB, and ATH are compared. The results show that as little as 3 phr MLG can replace up to 15 phr CB, as well as 3 phr ATH, without loss of material properties. Additionally, the nanocomposites displayed a strengthening of rheological and mechanical properties along with increased residue yield in fire tests. Thus, rubber nanocomposites with MLG are effective, multifunctional alternatives to conventional rubber formulations.
This paper of the month points out that, in flame retardancy, big things often come in small packages.
Multifunctional Graphene in Flame Retarded Polybutadiene/ Chloroprene/ Carbon Black Composites
Alexander Battig, Naïssa Abdou-Rahaman Fadul, Daniele Frasca, Dietmar Schulze, Bernhard Schartel
published in e-Polymers, Vol. 21, issue 1, pages 244 - 262, 2021
BAM Technical Properties of Polymeric Materials division