Reports: ND754253-ND7: Understanding the Effect of Graphene Oxide's C:O Ratio on Particle Polymer Intermolecular Forces and Resulting Macroscopic Properties

David E. Kranbuehl, PhD, The College of William and Mary

Summary of recent work and resulting manuscript

Over the past year we completed our research project on the effect of graphene oxide on reducing hydrolytic degradation in polyamide-11. A manuscript was written, submitted and accepted for publication in Polymer in late September. Work on the relationship of molecular weight and per cent crystallinity on the onset of the ductile to brittle transition in polyamide-11 is nearing completion and will result in a manuscript being written in the coming months. Recently are nanoparticle polymer interests have moved on to boron nitride nanotubes and their unique properties of exceptional strength but more important their high thermal conductivity while being an electoral insulator. This property could lead to their important role in conducting heat away from diodes and other electrical devices critical to many industries including petroleum. These nanoparticles when they are properly dispersed in the structural polymers used in electronic devices could be the key to achieving ever smaller and more powerful electronic applications.

Below is a summary of the past years results.

Polyamide-11 (PA11) is a widely-used engineering polymer. PA11 comprises the pressure sheath liner in contact with the production fluid at elevated temperature and pressure in flexible hoses for underwater transport of gas, oil, and crude to offshore platforms. As such, PA11 fulfills a vital role in the global economy. Degradation and failure of these hoses have far-reaching financial and environmental implications. Currently, the molecular weight of PA11 is used to predict the operational lifetimes of the PA11 liner where hydrolysis of PA11 is the mechanism for degradation in anaerobic environments such as the condition of underwater crude oil risers. Improving the properties of PA11 as a pressure sheath motivates research on the hydrolytic degradation of graphene oxide (GO) loaded PA11: GO-PA11 polymer nano-composite.

Graphene oxide (GO) was incorporated into polyamide-11 (PA11) via in-situ polymerization. The GO-PA11 nano-composite had elevated resistance to hydrolytic degradation. At a loading of 1 mg/g, GO to PA11, the accelerated aging equilibrium molecular weight of GO-PA11 was higher (33 and 34 kg/mol at 100 and 120 ˚C, respectively) compared to neat PA11 (23 and 24 kg/mol at 100 and 120 ˚C, respectively). Neat PA11 had hydrolysis rate constants (kH) of 2.8 and 12 ( 10-2 day-1) when aged at 100 and 120 ˚C, respectively, and re-polymerization rate constants (kP) of 5.0 and 23 ( 10-5 day-1), respectively. The higher equilibrium molecular weight for GO-PA11 loaded at 1 mg/g was the result of a decreased kH, 1.8 and 4.5 ( 10-2 day-1), and an increased kP, 10 and 17 ( 10-5 day-1) compared with neat PA11 at 100 and 120 ˚C, respectively. The decreased rate of degradation and resulting 40 % increased equilibrium molecular weight of GO-PA11 was attributed to the highly asymmetric planar GO nano-sheets that inhibited the molecular mobility of water and the polymer chain. The crystallinity of the polymer matrix was similarly affected by a reduction in chain mobility during annealing due to the GO nanoparticles’ chemistry and highly asymmetric nano-planar sheet structure.

In this work, the hydrolytic degradation of GO-PA11 and the effect GO had on the PA11 matrix crystallization was explored. The large immobile nano thin GO sheets and the intermolecular interaction between the GO’s surface C=O groups with the polyamide’s N-H groups significantly reduced molecular mobility in the GO-polymer and resulted in a reduction in the rate of crystallization and most importantly the rate of degradation by hydrolysis.