Orientation of channel die-compressed ultra-high molecular weight polyethylene

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997.Includes bibliographical references (leaf 46).by Yot Boontongkong.M.S

Templated aqueous synthesis of inorganics within carboxyl-containing block copolymer domains

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002.Includes bibliographical references.Template-directed, aqueous-based syntheses of nanoscale inorganic materials in carboxyl-functionalized block copolymer domains (nanoreactors) were demonstrated. First, the successful application of electroless metal deposition within the sub-surface lamellar domains of an amphiphilic block copolymer is presented. Several electroless metals were selectively deposited inside the interconnected network of the water-permeable block domains containing pre-loaded palladium, which served as the spatially localized deposition catalyst. The technique proved to be a facile means to rapidly deposit large amounts of metals within the hydrophilic block domains, despite limitations on the transport of plating reagents into the bulk templates. The simple process yielded novel nanocomposites consisting of alternating layers of metal with those of the hydrocarbon matrix. The extent of metal deposition within the bulk block copolymer templates was controlled by adjusting the deposition rate and deposition time. Second, unique self-assembled thin film templates comprising in-plane arrays of nanosized surface cavities were investigated. The micellar thin films, formed by direct casting of kinetically stable styrene(PS)-acrylic acid(PAA) block copolymer reverse micelles from toluene onto solid substrates, consisted of lateral hexagonal arrays of spherical PAA domains in PS matrices. It was shown that hydration and swelling of PAA upon treatment in a monovalent base (NaOH) aqueous solution led to a cavitation process that exposed the PAA cores to the free surface.(cont.) The use of these cavitated PAA domains as open nanoreactors for the synthesis of corresponding nanocluster arrays following aqueous sequestration of metal ions into carboxyl-containing domains was demonstrated. Metal loading of the PAA domains could alternatively be achieved in the absence of cavitation by omitting the base treatment step, where the loaded PAA domains remained embedded within the original PS matrix. Additional stability was imparted to the nanoclusters synthesized within these closed nanoreactors relative to their cavitated counterparts. The option to employ either the open or the closed micellar templates represents a useful versatility of this system.by Yot Boontongkong.Ph.D

Circular economy without chemicals controls? Evidence of recirculated toxic plasticizers in flexible PVC products

The global push towards a circular economy (CE) has led to increasing efforts to improve resource utilization efficiency, including plastics recycling. However, the presence of additives, especially those that are toxic, complicates plastics recycling in several ways. Without sufficient controls, the spread of hazardous additives via recycling activities represents a significant public health challenge, particularly among developing nations. This study demonstrates evidence of such uncontrolled recycling, based on an investigation of four household flexible PVC product groups available in Thailand. A versatile pyrolysis/thermal desorption gas chromatography-mass spectrometry (Py/TD-GC-MS) method was employed to simultaneously screen 18 target plasticizers in these products. Di-(2-ethylhexyl) phthalate (DEHP) and diisononyl phthalate (DINP) are the most frequently detected primary plasticizers. DEHP is dominant in vinyl boots, flooring sheets, and hoses, while DINP is dominant in cable sheaths, likely due to a spill-over effect from the EU Restriction of Hazardous Substances (RoHS) directive. Chlorinated paraffins (CPs) are secondary plasticizers that are also detected in most samples, except for boots. The other plasticizers detected include other ortho-phthalates and non-phthalates. These results provide insight into combinatory patterns of plasticizer ‘cocktails’, that comprise restricted, as-yet-unrestricted, and non-restricted plasticizers, embedded in the same individual samples, with a maximum of seven plasticizers found in a single cable sheath. These findings indicate the existence of potentially risky recycling practices that target embedded plasticizers to save cost, without due consideration of their inherent toxicity. Proper interventions are necessary to ensure that CE and chemical safety can be synergized

A Simple Top-Down/Bottom-Up Approach to Sectored, Ordered Arrays of Nanoscopic Elements Using Block Copolymers

A top-down/bottom-up approach is demonstrated by combining electron-beam (e-beam) lithography and a solvent annealing process. Micellar arrays of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) with a high degree of lateral order can be produced on a surface where sectoring is defined by e-beam patterning. The e-beam is used to crosslink the block copolymer (BCP) film immediately after spin-coating when the BCP is disordered or in a highly ordered solvent-annealed film. Any patterns can be written into the BCP by crosslinking. Upon exposure to a preferential solvent for the minor component block followed by drying, cylindrical nanopores are generated within the nonexposed areas by a surface reconstruction process, while, in the exposed areas, the films remain unchanged. Nickel nanodot arrays can be placed over selected areas on a surface by thermal evaporation and lift-off process