Date

1-1-2020

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Polymer Science and Engineering

First Adviser

Raymond A. Pearson

Abstract

Selective laser sintering (SLS) continues to be a promising additive manufacturing process, in which three dimensional shapes are produced through laser sintering and resurfacing of a powder bed. The structural changes of a polyamide 11/carbon black (PA11/CB) powder during a UV-laser sintered printing process were analyzed to ultimately serve as a benchmark for a PA11/CB/SNP nanocomposite printed material. Samples printed with increasing laser area energy density were compared in terms of crystalinity, melt temperature, tensile behavior, essential work of fracture, density, molecular weight and amorphous chain rigidity. A molecular weight increase is found to occur in a stepwise fashion, with the tensile elongation, ultimate tensile strength, essential work of fracture and density following a similar behavior. X-ray diffraction revealed slight changes in dhkl spacing, which correlated well with slight melting peak shoulders shown in differential scanning calorimetry. Similar changes to the mobile amorphous phase were calculated suggesting partial metastable δ′ crystal phase content due to unusual solidification. PA11/CB/SNP nanocomposite powder was developed with both 50 nm and 25 nm SNP. Both solid state shear pulverization and centrifugal mixing proved successful in powder blending. Powder flow measurements at increasing temperature have shown enhanced flow behavior at processing temperatures with increasing SNP. Increases in stiffness and strength as well as decreases in linear reciprocating wear suggest good reinforcement of particle layer boundaries, however brittle behaviour of the higher SNP loaded PA11/CB/SNP parts suggest diminished sintering. Ultimately, it was concluded that colloidal silica can be utilized to greatly change both powder flow and mechanical properties of a SLS printing powder, with these studies have providing a framework for the feasibility of processing and printing nanoparticle coated polymer powders.

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