Retention of mechanical performance of polymer matrix composites above the glass transition temperature by vascular cooling

An actively cooled vascular polymer matrix composite containing 3.0% channel volume fraction retains greater than 90% flexural stiffness when exposed continuously to 325 °C environmental temperature. Non-cooled controls suffered complete structural failure through thermal degradation under the same conditions. Glass–epoxy composites (T g = 152 °C) manufactured by vacuum assisted resin transfer molding contain microchannel networks of two different architectures optimized for thermal and mechanical performance. Microchannels are fabricated by vaporization of poly(lactide) fibers treated with tin(II) oxa-late catalyst that are incorporated into the fiber preform prior to resin infiltration. Flexural modulus, material temperature, and heat removal rates are measured during four-point bending testing as a function of environmental temperature and coolant flow rate. Simulations validate experimental measurements and provide insight into the thermal behavior. Vascular specimens with only 1.5% channel volume fraction centered at the neutral bending axis also retained over 80% flexural stiffness at 325 °C environmental temperature. Polymer matrix composites (PMCs) are susceptible to reduced structural performance at elevated temperatures, such as those experienced during high speed flight [1–3], vehicle transportation [4–6], and during cycling of batteries, fuel cells, and other electronics [7–9]. Typical polymer matrices, such as epoxy, polyester, and vinyl-ester, have glass transition temperatures (T g) at or below 200 °C, forcing the use of alternative materials such as metals and ceramics at service temperatures [3]. Subjecting a composite to high temperature, even for short time periods, can cause permanent damage, including delamination, matrix cracking, plastic deformation, and ultimately combustion and fire [10–13]. As an alternative, circulation of coolant through microvascular channels embedded directly into the PMC can regulate temperature by removing heat [14–16], potentially enabling safe structural performance under high thermomechanical loading. In PMCs, vascular networks have been fabricated by solder removal [17,18], manual extraction of a solid wire [19–21], integration of hollow tubules or fibers [22–28], and Vaporization of Sacrificial Components (VaSC) [29–31]. Unlike most other methods which are restricted to straight channels with one-dimensional connectivity, VaSC using sacrificial fibers (SF) allows for three-dimensional, interconnected vascular architectures. To create a hollow channel poly(lactic acid) (PLA) SFs are integrated into textile weaving or braiding operations, survive standard composite manufacturing processing, and then are subsequently removed during a 200 °C post-cure [30]. When manufactured to minimize distortions to the structural fiber architecture, channels had minimal effect on tensile and compressive strength and modulus Kozola et al. [14] studied active cooling in a vascularized epoxy fin …