In situ crosslinking of surface-initiated ring opening metathesis polymerization of polynorbornene for improved stability.

HYPOTHESIS: In situ crosslinking is expected to increase the solvent stability of coatings formed by surface-initiated ring opening metathesis polymerization (SI ROMP). Solvent-associated degradation limits the utility of SI ROMP coatings. SI ROMP coatings have a unique capacity for post-functionalization through reaction of the unsaturated site on the polymer backbone. Any post-reaction scheme which requires a liquid solvent has the potential to degrade the coating and lower the thickness of the resulting film. EXPERIMENTS: We designed a macromolecular crosslinking group based on PEG dinorbornene. The PEG length is tailored to the expected mean chain to chain distance during surface-initiated polymerization. This crosslinking macromer is randomly copolymerized with norbornene through SI ROMP on a gold coated substrate. The solvent stability of polynorbornene coatings with and without PEG dinorbornene is quantitatively determined, and the mechanism of degradation is further supported through XPS and AFM analyses. FINDINGS: The addition of the 0.25mol% PEG dinorbornene significantly increases the solvent stability of the SI ROMP coatings. The crosslinker presence in the more stable films is supported with observable PEG absorbances by FTIR and an increase in contact angle hysteresis when compared to non-crosslinked coatings. The oxidation of the SI ROMP coatings is supported by the observation of carbonyl oxygen in the polynorbornene coatings. The rapid loss of the non-crosslinked SI ROMP coating corresponds to nanoscale pitting across the surface and micron-scale regions of widespread film loss. The crosslinked coatings have uniform nanoscale pitting, but the crosslinked films show no evidence of micron-scale film damage. In all, the incorporation of minimal crosslinking content is a simple strategy for improving the solvent stability of SI ROMP coatings.

Biodynamics model for operator head injury in stand-up lift trucks.

Biodynamics and injury potential of operators in stand-up rider lift truck accidents have been investigated with a special focus on head injury. An anthropomorphic test device (ATD) model was used as an operator surrogate in computer simulations of off-the-dock (OTD) and tip-over (TO) accidents. The biomechanical model representing the ATD was developed based on rigid body segments, and then combined with a rigid body truck model in the accident simulations. The operator compartment of the truck model was enclosed with a rear door. The computed kinematics are in agreement with the results of previous experimental testing. A 2D finite element model of the head was created to compute head impact decelerations in the sagittal plane. Values of the head injury criterion for the TO cases were computed from the model and shown to compare favourably with experimental values. The results advance the state of knowledge concerning injury potential in TO and OTD accidents and simulation models for such accidents.