Abstract
Abstract Polyolefins used in building materials and furniture require the use of flame-retardant (FR) additives to improve their fire safety. Such additives should be safe to humans and the environment, and preferably bio-based. In the present work, the FR performance of unmodified and chemically modified technical lignins was compared to that of the ammonium polyphosphate/pentaerythritol (APP/PER) intumescent system in a polypropylene (PP) matrix. Micro-scale combustion calorimetry (MCC) was used to study the peak heat release rate (PHR), temperature at PHR (TPHR), total heat release (THR) and char yield upon thermal decomposition of milligram-scale specimens. The PP/lignin composites showed up to 41% lower PHR and up to 36% lower THR compared to pure PP as well as large char residues. Based on the same parameters, especially the PP/lignin composites made with modified lignins outperformed the reference PP/APP/PER system and the PP/APP/lignin composites where unmodified lignin was used with APP. The most promising PP/lignin composites were prepared with partially demethylated/demethoxylated and depolymerised kraft lignin (‘CatLignin’), modified by the Mannich reaction to a nitrogen content of 13.5%.
Highlights
The flammability and thermal decomposition of thermoplastic polymers such as polypropylene (PP) limits theirThe fire behaviour of materials is commonly assessed by measuring the amount of thermal energy released during their combustion
The ammonium polyphosphate (APP)/PER (1/1) composite was better than the ammonium polyphosphate/pentaerythritol (APP/PER) (3/1) composite and showed similar peak heat release rate (PHR) and slightly better total heat release (THR) and char yield than the CL and hydrolysis lignin (HL) composites without any APP
The results show that CL-M and kraft lignin (KL)-M are potential substitutes for PER in the APP/PER system, resulting in a decrease in PHR and no deterioration of THR or char yield
Summary
The fire behaviour of materials is commonly assessed by measuring the amount of thermal energy released during their combustion. Quantities such as peak heat release rate (PHR) and total heat release (THR) can be measured using, e.g., a micro-scale combustion calorimeter (MCC) or. Widsten et al.: Lignin flame retardants a cone calorimeter (CCM) It should be noted, that similar quantities obtained using different test methods are not directly comparable due to the differences in the test conditions, specimen configurations and several other factors. As an example of fire behaviour evaluation, it has been observed that PHR, THR (measured using CCM) and mass loss rate (measured using TGA) tend to improve (i.e., decrease) as a function of increasing lignin content in the composite material (Costes et al 2017). Any inert gases formed can dilute the combustible gases
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