Neil R. Edmonds

Development and design of binder systems for titanium metal injection molding: An overview

Titanium metal injection molding (Ti-MIM) has been practiced since the late 1980s. Logically, the Ti-MIM practice follows the similar processes developed for the antecedent materials such as stainless steel and ceramics. Although Ti-MIM is a favorite research topic today, the issue of convincing the designers to use Ti injection-molded parts still exists. This is mainly because of the concern about contamination which seems unavoidable during the Ti-MIM process. Much information about the binder formulation, powder requirements, debinding, and sintering is available in the literature. There are several powder vendors and feedstock suppliers. However, most of the binders in the feedstock are proprietarily protected. The disclosed information on the binders used for formulating powder feedstock is very limited, which in turn discourages their adoption by engineering designers. This overview intends to discuss some of major binder systems for Ti-MIM available in the literature. It serves to provide a guideline for the Ti-MIM practitioners to choose a suitable powder feedstock.

Vegetable oil thermosets reinforced by tannin–lipid formulations

Totally bio-based thermosetting polymers which are comparable to synthetic polyester thermosets have been prepared from copolymerization of condensed tannin-fatty acid esters with vegetable oils. Oxidative copolymerization of tannin linoleate/acetate mixed esters with linseed oil and tung oil produced polymer films ranging from soft rubbers to rigid thermosets. Tannin incorporation into the formulations was essential for the final product to achieve necessary mechanical strength. Films had ambient modulus values between 0.12 and 1.6 GPa, with glass transition temperatures ranging from 32 to 72 °C and calculated crosslink densities of 1020-57,700 mol m⁻³. Film stiffness, T(g) and crosslink density increase with greater tannin linoeate/acetate content due mainly to this tannin component providing rigidity through polyphenolic aromatic rings and unsaturated chains as crosslinking sites.

Prevulcanized Natural Rubber Latex/Modified Lignin Dispersion for Water Vapour Barrier Coatings on Paperboard Packaging

Modified natural rubber latex can be used as paperboard barrier coating in order to replace unrecyclable wax coating material. Natural rubber latex (NRL) was prevucanized in different time interval and the efficiency of crosslinking were determined by swelling ratio test. Prevulcanized natural rubber latex (Pre-VNRL) was blended with modified lignin dispersion to decrease sticking tendency of the coatings. Particle size of lignin dispersion was reduced by Mannish reaction using octylamine which can increase hydrophobility in lignin. Compared with Pre-VNRL coating, a reduction of water vapour transition rate (WVTR) was observed in blendingcoated paper. Such moisture-barrier behaviour is attributable to a good compatibility of the nanosized modified lignin particles with rubber. The blocking (sticking) tendency decreased with the content increase of lignin due to stiffness of lignin.

Two-Dimensional FTIR as a Tool to Study the Chemical Interactions within Cellulose-Ionic Liquid Solutions

In this study two-dimensional FTIR analysis was applied to understand the temperature effects on processing cellulose solutions in imidazolium-based ionic liquids. Analysis of the imidazolium ion νC2–H peak revealed hydrogen bonding within cellulose solutions to be dynamic on heating and cooling. The extent of hydrogen bonding was stronger on heating, consistent with greater ion mobility at higher temperature when the ionic liquid network structure is broken. At ambient temperatures a blue shifted νC2–H peak was indicative of greater cation-anion interactions, consistent with the ionic liquid network structure. Both cellulose and water further impact the extent of hydrogen bonding in these solutions. The FTIR spectral changes appeared gradual with temperature and contrast shear induced rheology changes which were observed on heating above 70°C and cooling below 40°C. The influence of cellulose on solution viscosity was not distinguished on initial heating as the ionic liquid network structure dominates rheology behaviour. On cooling, the quantity of cellulose has a greater influence on solution rheology. Outcomes suggest processing cellulose in ionic liquids above 40°C and to reduce the impacts of cation-anion effects and enhance solubilisation, processing should be done at 70°C.

Crosslinkable poly(vinyl acetate) emulsions for wood adhesive

Purpose – The purpose of this paper is to enhance the water resistance and the heat resistance of poly(vinyl acetate) (PVAc) emulsion adhesive, by providing the emulsion with controllable thermosetting capability.Design/methodology/approach – Emulsion polymerisation was used to synthesise PVAc/VeoVa 10 copolymers with varying proportions of acetoacetoxyethyl methacrylate (AAEM) incorporated in the copolymer chains. The AAEM component provided sites for crosslinking the chains via reaction of diamines with AAEM. The emulsion copolymers formed crosslinked films on addition of a range of diamines, during drying at ambient temperature. Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy were employed to characterise the copolymerisation and crosslinking reaction. Glass transition temperatures of the polymer films were measured using dynamic mechanical thermal analysis to quantify the effects of copolymer composition variation and crosslinker. The performance of the crosslinked ...

Debinding Kinetics of a Water Soluble Binder System for Titanium Alloys Metal Injection Moulding

A water soluble binder system is used to prepare Ti-6Al-4V and NiTi pre-alloyed powder feedstock. The binder dissolution and transport kinetics through the porous powder skeleton are studied for various powder morphologies and powder loadings from 60 to 69.5 vol.%. The binder removal behaviours are evaluated with different debinding time intervals. The focus of this work is to investigate the influences of shaping pressure, specimen thickness and water bath temperature on the binder extraction behaviour.

Organotin carboxylate catalyst in urethane formation in a polar solvent: an experimental and computational study

Organotin carboxylates are important catalysts in aliphatic urethane synthesis. They are widely used in two component urethane systems such as casting systems, high performance coatings and in the synthesis of one-component moisture cure urethane pre-polymers for coatings. In most of these systems, a solvent is used to reduce the viscosity to assist application. In general, aromatic hydrocarbon solvents such as xylene, R100 or oxygenated solvents (e.g. esters) are used. In this paper, a detailed investigation of the catalytic mechanism of organotin carboxylate in urethane synthesis in a polar medium is investigated using experimental and computational methods. There is evidence that the dominant catalyst for organotin carboxylate catalysis of aliphatic isocyanate in urethane formation in a polar medium is organotin alkoxide. In this work, DFT studies on B3LYP/LANL2DZ/6-31+G** level of theory with the CPCM solvent model was used to study the reactivity between isocyanate and alcohol in the presence of a selected organotin catalyst in different mediums. The theoretical studies were supported by experimental evidence.

Water debinding behaviour of water soluble Ti-MIM feedstock

Abstract A water soluble polyethylene glycol (PEG) based binder system was used to formulate three feedstocks containing prealloyed Ti–6Al–4V, NiTi and blended elemental Ni/Ti powders respectively. The selection of these metal powders was to investigate the effect of powder characteristics such as particle size and particle shape. Various solid loadings were investigated in these feedstocks. The water debinding behaviours were systematically studied in terms of debinding temperature, time, sample thickness, powder characteristics and solid loading. Corresponding debinding rate was calculated from the measurements using a shrinking core reaction kinetic model.

Developing polymeric antireflective coatings

As polymers become more widely used in optics antireflective coatings need to be designed specifically to suit these new components. Modifications are being made to the current high temperature coating process to allow for inorganic metal oxides to be applied to polymer optics. This is not however the only hurdle that needs to be overcome to produce a satisfactory antireflective coating on polymers. Inorganic metal oxides and polymer components have a significant difference in thermal expansion meaning that defects such as delamination and cracking can occur. These defects significantly shorten the lifetime of the optical component. A new antireflective coating has been developed that has a similar thermal expansion coefficient to that of the polymer substrate, meaning that defects caused by thermal stress do not occur. These are polymeric coating with a refractive index of 1.31 and 1.34, lower than that of magnesium fluoride (MgF2) at 1.38. These coatings have antireflective properties superior to those of current commercially available single layer inorganic antireflective coatings. Polymer antireflective coatings cannot be applied by vacuum deposition. Dip coating was evaluated as a method for film application. Dip coating allows control of the film thickness through varying the properties of the coating solution. It also allows for uniform films that can be inspected visually for variances.

An antireflective coating suitable for use on polymer optics

Although metal halide anti-reflective (AR) coatings are widely used by manufacturers of electronics equipment, high application temperatures mean that they can only easily be applied to glass substrates. Screens made from plastics materials can be coated but the process requires additional steps to prevent damaging the substrate. A new, easily applied anti-reflective coating has been designed which can be applied to both plastic and glass substrates. The single layer coating applied to an acrylic substrate has proven to be better performing than current commercial single layer anti-reflective coatings. This performance has been achieved from an amorphous fluoropolymer solution which is dip coated onto the substrate.