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Polymer Degradation in Inkjet Printing
[Thesis]. Manchester, UK: The University of Manchester; 2015.
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Abstract
Inkjet printing is a widely used micrometre accuracy controlled deposition technique forpicolitre quantities of ink. Polymeric materials are a vital component in many inkjetformulations. Inkjet technology has been applied to many different applications beyondeveryday home and office use, such as: industrial product marking, fabrication of printedelectronics and printing of biomaterials. This technology has many advantages overtraditional manufacturing techniques: it allows the direct printing of computer generatedimages and patterns without the need for costly and time consuming production of mouldsor patterned substrates. Additive manufacturing such as inkjet and 3d printing have thepotential to usher in a second industrial revolution where economies of scale are maderedundant.For fabrication of functional materials it is vital that the ink loaded into the printermaintains its physical properties after undergoing the high stress inkjet printing process.We demonstrate for the first time molecular weight degradation in continuous inkjetprinting and that it proceeds by a different mechanism to that already reported for drop ondemand printing systems. The ejection of drops from the print head using continuousinkjet technology results in no change in molecular weight distribution to any highmolecular weight ink solute. However, the pumps and filters that comprise the inksystems are shown to degrade polymeric solutes by a long time scale random degradationmechanism.It is postulated that polymer degradation in inkjet printing is due to the polymerundergoing its coil-stretch transition in the printhead and undergoing the printing processin a vulnerable low entropy state. In order to produce robust degradation resistant inks afamily of high molecular weight branched polymers are synthesised. These branchedmaterials shows enhanced stability to the high shear printing process and elevatedmaximum printable concentrations when compared to linear polymeric material.Rheological and spectroscopic techniques are applied to understand the flow behaviourand mechanism of degradation of polymeric inks during the inkjet printing process. It isfound that polymer degradation during inkjet printing produces highly reactive radicalspecies; with which it is possible to perform controlled mechanochemistry.