Browsing by Author "Anagwu, Festus Ifeanyi"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Cure kinetics, glass transition advancement and chemo-rheological modelling of an epoxy vitrimer based on disulphide metathesis
    (Elsevier, 2023-11-03) Anagwu, Festus Ifeanyi; Skordos, Alexandros A.
    This study develops cure and chemo-rheological models for a vitrimeric system appropriate for use as matrix in continuous fibre composites based on a disulphide-endowed amine/epoxy formulation. The focus is on the processing conditions relevant to liquid composite moulding. Kinetics is investigated using Differential Scanning Calorimetry. An autocatalytic model is developed, simulating the reaction with an average reaction rate error of 5.2 % and degree of cure error of 3 %. The viscosity development is modelled at relatively low degrees of cure, focusing on the liquid moulding infusion window, yielding results with an average relative error of 4.8 %. The glass transition temperature advancement is represented by the Di Benedetto equation, whilst the topological transition temperature of the system is determined using stress relaxation experiments and found to be 149.5 °C. These results set the scene for the development of composites based on the matrix system investigated in this work.
  • Thumbnail Image
    ItemOpen Access
    High glass transition catalyst-free polybenzoxazine vitrimer through one-pot solventless method
    (Elsevier, 2025-04) Anagwu, Festus Ifeanyi; Dossi, Eleftheria; Skordos, Alexandros A.
    A high glass transition polybenzoxazine has been synthesised by a one-pot solventless method via the Mannich condensation of a phenolic disulphide, paraformaldehyde and aniline. The solventless process reduces synthesis time, material costs, and the need for post-synthesis purification. The polybenzoxazine exhibits a glass transition temperature (Tg) of 155 °C and thermosetting behaviour below this temperature. Dynamic disulphide bond metathesis associated with a topological freezing temperature of 78 °C and an activation energy of 127 kJ/mol delivers vitrimeric functionality with fast, catalyst-free stress relaxation above Tg. This material fully relaxes stress within 5 s at 190 °C, with thermal degradation beginning above 250 °C. It exhibits a glassy modulus of 3.6 GPa, high char yield (57.4 %) translating to a high limiting oxygen index (LOI) of 40.5 % and excellent environmental resistance, as evidenced by low water uptake (1.4 %) after immersion at 75 °C for 31 days. The combination of environmental resistance, due to thermosetting character, high glass transition, facile synthesis, high char yield, good processability, and fast stress relaxation position this polybenzoxazine as a promising candidate matrix system for repairable aerospace thermosetting continuous fibre composites.
  • Thumbnail Image
    ItemOpen Access
    High-performance vitrimeric benzoxazines for sustainable advanced materials: design, synthesis, and applications
    (Wiley, 2022-10-26) Anagwu, Festus Ifeanyi; Thakur, Vijay Kumar; Skordos, Alexandros A.
    Polybenzoxazines are high-performance materials capable of replacing conventional thermosets such as phenolics, epoxies, and bismaleimides in composites manufacturing due to their excellent thermomechanical and chemical behavior. Their versatility and compatibility with biobased precursors make them an attractive option as composite matrices. Like other thermosets, polybenzoxazines are not recyclable and cannot be reprocessed. Incorporating dynamic bonds in benzoxazine monomers can produce vitrimeric polybenzoxazines, which can potentially overcome this limitation and can be tuned to exhibit smart functionalities such as self-healing and shape memory. Dynamic bond exchange mechanisms for vitrimer development such as transesterification, imine bond, disulfide exchange, transamination, transcarbamoylation, transalkylation, olefin metathesis, transcarbonation, siloxane-silanol exchange, boronic ester, silyl ether exchange, and dioxaborolane metathesis are potentially applicable to benzoxazine chemistry, with disulfide bond and transesterification having successfully vitrimerized benzoxazines with topological transitions at −8.5 and 88 °C, respectively. Benzoxazine vitrimers featuring glass transitions of 193, 224, and 222–236 °C are now known. These place polybenzoxazines at the forefront of the development of reprocessable and recyclable thermosetting polymers and composite matrices.