Efficiency comparison of hyperbranched polymers as toughening agents for a one-part epoxy resin
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UNESP – Univ. Estadual Paulista – Guaratinguetá Faculty of Engineering, Guaratinguetá (SP) 12516-410, Brazil
Laura Ascione and Veronica Ambrogi
UNINA – University of Naples “Federico II” – Department of Chemical, Materials, and Production Engineering, Napoli (NA) 80125, Italy
Maria O. H. Cioffi
UNESP – Univ. Estadual Paulista – Guaratinguetá Faculty of Engineering, Guaratinguetá (SP) 12516-410, Brazil
Paola Persico
CNR – National Research Council - Institute for Macromolecular Studies (ISMAC), Milano 20133, Italy (Received 5 September 2014; accepted 30 January 2015)
A previously synthesized hyperbranched poly(butylene adipate) (HPBA) polymer was compared with a commercial dendritic polyol (HPOH) as a toughening agent for a commercial one-part epoxy resin. Both modifiers were added in weight percentages of 1, 3, 5, and 10%. The modified epoxies were characterized using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), melt rheological tests, and linear elastic fracture mechanics. Blend morphology and matrix–modifier interactions were evaluated using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analysis, respectively. The toughness-improvement effect was achieved without substantial impairment of thermomechanical properties or degradation of the thermal stability of the epoxy resin. A meaningful decrease in viscosity was achieved with both modifiers, contributing to an easier infusion processability. No evidence of new chemical linking was found although phase separation was observed by SEM, leading to the conclusion that only interfacial linkage occurs between modifiers and epoxy chains. SEM analysis also clearly shows the fracture mode changing from brittle to ductile by addition of modifiers, which was more evident for blends of HPBA.
I. INTRODUCTION
Polymers have been widely used as conventional material substitutes due to their range of thermal and mechanical properties and low cost. The crosslinked epoxy resin system, an outstanding material, is considered to be the most attractive and commonly applied one, as it offers a large range of formulations and structural characteristics that allow different applications varying from simple objects to aerospace parts.1,2 Although epoxy resins exhibit some desired features for engineering applications, a significant restriction is caused by the high crosslink density that affects the toughness characteristics. This latter property has a strong influence on properties such as impact, fatigue, and damage tolerance, among others.3,4 Efforts to improve toughness have involved the use of rubbers, thermoplastics, and inorganic materials, such as silica nanoparticles.3,5 Reactive liquid rubbers have been Contributing Editor: Linda S. Schadler a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.41
the most widely used materials because they form a homogeneous solution during preparation, beyond a second phase precipitation after curin
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