A new nanoscale catalytic flame retardant system was developed and integrated into a polypropylene polymer matrix in a research article published in the journal Material Letters. This study offered a unique common catalyzed charring technology that combines the benefits of nanoscale flame retardant technologies with catalyzed charring.
Study: An innovative binary nanocatalytic flame retardant system to improve the fire safety performance of polypropylene. Image credit: prapann / Shutterstock.com
Increased flame protection of polypropylene polymer
Polypropylene (PP) polymer burns completely without leaving any obvious char. Carbon atoms in polypropylene’s primary chains are burned to form gas phase chemicals such as carbon dioxide and carbon monoxide.
As a consequence, if the C atoms are catalytically captured in the form of carbonization, the combustion of polypropylene is slowed down, leading to a slower rate of heat emission. As a result, catalyzed carbonation has emerged as a new flame retardant method.
On the other hand, the catalyzed charring effect of typical transition metals on polyolefin is only marginally acceptable. Establishing a particularly effective nanoscale catalyzed carbonization and flame retardancy technology is crucial to improving flame retardancy in polymers.
Improve catalytic charring by using solid acids
Several solid acids, such as organically modified clay or zeolite, have been used in connection with carbonization catalysts. These combined catalysts have been successful in increasing the production of polymer carbon.
The role of the graph
Graphene has gained a lot of interest in the flame retardant industry due to its 2D shape. It has many binding points for immobilization of foreign nanoparticles (NP).
Graphene is widely known for its lamella structure, and the highly dispersed graphene contributes to the physical barrier, leading to a slower rate of heat loss. Nanofilms with reduced graphene oxide (RGO) are coated with NPs of phosphomolybdic acid (PMoA) with acid stains.
RGO-PMoA acts as a PP pyrolytic catalyst. RGO-PMoA’s protic acid sites engage the PP backbones, promoting aromatization and dehydration of PP degradation products.
As soon as a small amount of RGO-PMoA is added, additional light hydrocarbons (HC) and aromatics are produced. RGO-Ni dehydrates and assembles such aromatic and small molecules to generate additional carbonization layers. Organic decomposition chemicals with smaller carbon numbers and aromatic components are more likely to promote graphitic carbon formation.
What was the research methodology?
In this study, based on the decorated surface of reduced graphene oxide (RGO), a new catalyzed carbonization and flame retardancy system was developed. The effect on PP’s burning behavior was then investigated. The mechanics of catalytic charring and flame retardancy were shown.
The polypropylene polymer composite containing 1% RGO-Ni and 1% RGO-PMoA was found to have the highest carbon residue and the greatest flame retardant property. The optimal proportion of RGO-Ni and RGO-PMoA affects catalyzed charring and flame retardancy.
How does the charring process contribute to flame retardancy?
Transition metals with catalyzed carbonization properties include nickel, iron and cobalt. However, the solitary element in transition metals is not favorable for coal production. Graphene nanofilms provide micro-scale reactors and carbonizing templates with barrier effects.
The well-distributed graphene, which offers suitable settings for catalyzed carbonation, slows the release of gaseous decomposition products of polypropylene. Instead of completely burning to gaseous components without leaving any residue, the flammable polypropylene chains are catalytically charred to the thermally stabilized and non-combustible carbon residue.
As a result of barrier effects on heat and mass transfers, the generated carbon-based layer that coats inhibits the combustion of the components inside. As a result, RGO-PMoA complements RGO-Ni to increase the flame retardancy of polypropylene.
Highlights of the study
The surface properties of reduced graphene oxide nanofilms were altered by adding Ni and PMoA NPs. The chemical composition, content and structure were carefully examined. PMoA NPs were bonded to the RGO surface by electrostatic contact. These graphene-based nanoparticles were evenly distributed in the polypropylene matrix.
On polypropylene, the hybrid catalyst (RGO-PMoA: RGO-Ni = 1: 1) showed outstanding catalyzed charring and flame retardant properties. Due to its protonic acid nature, RGO-PMoA degraded polypropylene catalytically to additional aromatics and finer molecules, which were susceptible to catalyzed carbonization of RGO-Ni.
The properties of this hybrid catalyst serve as a reference for the development of high-performance polymeric nanocomposites with outstanding flame retardancy and minimal nanofill doping.
Wang, S., & Zhang, Y. (2022). An innovative binary nanocatalytic flame retardant system to improve the fire safety performance of polypropylene. Material Letters. Available on: https://doi.org/10.1016/j.matlet.2022.132663
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