Thermal shrinkage and heat capacity of monolithic polymeric physical aerogels. (1st December 2020)

• Record Type: Journal Article
• Authors: Nagendra, Baku; Antico, Pasqualmorica; Daniel, Christophe; Rizzo, Paola; Guerra, Gaetano
• Is Part Of: Polymer. Volume 210(2020)
• Publication Date: 2020-12-01
• Subjects: poly(2, 6-dimethyl-1, 4-phenylene)oxide (PPO) -- Syndiotactic polystyrene -- DSC -- Aerogels and foams -- BET surface area; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2020.123073
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: Monolithic physical aerogels based on semicrystalline linear polymers are suitable for molecular separation, catalysis, and thermal insulation. These low-density materials generally exhibit thermal shrinkage in their pre-melting region. Differential Scanning Calorimetry (DSC) shows that aerogel thermal shrinkages occur with relevant step decreases of heat capacity (ΔCp < 0). For physical aerogels based on the thermodynamically stable β form of syndiotactic polystyrene (sPS), a positive heat capacity step associated with glass transition ( T g ) and a negative heat capacity step associated with thermal shrinkage are well separated. As for poly (2, 6-dimethyl-1, 4-phenylene)oxide (PPO), which exhibits the rather unique closeness of T g and T m, the two phenomena are superimposed and a regular increase of heat capacity with porosity, going from positive to progressively more negative values is observed. Negative heat capacity steps are not present for thermal shrinkage of polymer foams, which exhibit high porosity but the low surface area. On the basis of the present study, simple and fast DSC scans allow accurate evaluation of temperatures of thermal shrinkage of monolithic physical polymer aerogels. Graphical abstract: Image 1 Highlights: DSC study of monolithic physical aerogels based on semicrystalline linear polymers. Thermal shrinkage of aerogels occur with relevant negative step decreases of heat capacity. As for PPO, a regular change of heat capacity with porosity is described. Negative heat capacity steps are not present for thermal shrinkage of polymer foams. DSC scans allow accurate evaluation of temperatures of shrinkage of polymer aerogels.