Thermal Activation of Mendable Epoxy through Inclusion of Microcapsules and Imidazole Complexes

<p>Epoxy resin was encapsulated in poly(urea–formaldehyde) microcapsules using an in situ dispersion polymerization technique. The efficiency of Ni and Cu–imidazole complexes as latent hardeners was compared to that of 2-methylimidazole. Calorimetric studies revealed higher reactivity of the nickel complex toward oxirane functionalities. Both the complexes could effectively cure the epoxy released from within the microcapsules in the event of damage followed by thermal treatment. The curing could be effected at lower temperature (<i>T</i>_onset = 145°C) using [Ni(2-Me-ImidH)₄Cl]Cl as compared to [Cu(2-Me-ImidH)₄Cl]Cl (<i>T</i>_onset = 152°C). A healing efficiency of 100 ± 2% could be achieved at 30% microcapsule loading, irrespective of the type of metal complex used. </p

Sustainable Bis-benzoxazines from Cardanol and PET-Derived Terephthalamides

This paper deals with the preparation of sustainable benzoxazines that exhibit enormous potential to compete with the existing petro-based advance performance thermosets. The phenolic component used for the synthesis of benzoxazine is derived from naturally occurring cardanol, which is obtained from cashew nut tree, Anacardium occidentale. Polyethylene terephthalate (PET) was chosen as a sustainable feedstock for the amine fraction used to prepare the benzoxazine monomer containing amide linkages. Microwave-assisted aminolysis of PET was performed to obtain bis­(amino-ethyl) terephthalamide (BAET) and α,ω-aminoligo­(ethylene terephthalamide) (AOET), which were employed as the difunctional amine for the preparation of bis-benzoxazines. In comparison to the traditional method, microwave-assisted aminolysis of PET was found to be significantly faster, and the reaction completion time could be brought down appreciably. Mannich-like condensation of cardanol with PET-derived terephthalamides and paraformaldehyde led to the formation of bis-benzoxazines with amide linkages, the structure of which was confirmed through FT-IR and ¹H NMR spectroscopy. The curing behavior of the bis-benzoxazines was studied using nonisothermal differential scanning calorimetry. The presence of amide linkages in addition to the polar group formed during the ring opening of benzoxazines led to the improvement in adhesive strength, which was quantified in terms of lap shear strength

Toughening of Epoxy with Preformed Polyethylene Thermoplastic Filler

<div><p>The potential of polyethylene as a thermoplastic filler towards improving the fracture properties of epoxy resin was explored. Oxo-degradable films were subjected to thermo-oxidative exposure, and the oxidized polyethylene (OPE) was extracted with acetone to remove low molecular weight products (APE). The presence of functionalities led to its homogenous dispersion in the epoxy matrix. Blending of epoxy with OPE and APE led to significant improvement in both quasi-static and impact properties, as evidenced by 44% increase in G_IC and 21% increase in impact strength at loadings of 3% w/w. The strain rate sensitivity of the composites was also investigated.</p></div