Sumin Kim

Curing behavior and viscoelastic properties of pine and wattle tannin-based adhesives studied by dynamic mechanical thermal analysis and FT-IR-ATR spectroscopy

This study investigated the curing behavior and viscoelastic properties of two types of tannin-based adhesives, wattle and pine, with three hardeners: paraformaldehyde, hexamethylenetetramine and TN (tris(hydroxylmethyl)nitromethane), by FT-IR-ATR spectroscopy and dynamic mechanical thermal analysis (DMTA). Using FT-IR-ATR spectroscopy, the chemical structures of tannin-based adhesives were determined and the degrees of curing as a function of temperature and time were compared with the conversion degrees of the hydroxyl groups. Paraformaldehyde was shown to be more reactive with wattle tannin than the other hardeners, while hexamethylenetetramine was the most reactive with the pine tannin. As the quantity of hardener was increased, the conversion degree also increased. The storage modulus (E′), loss modulus (E′′) and loss factor (tan δ) of each adhesive system were obtained by DMTA. With increasing temperature, as the tannin-based adhesives hardened, the storage modulus (E′) increased in all adhesive systems. The curing behavior results obtained by DMTA showed a similar tendency as seen from the FT-IR-ATR spectroscopy results. The curing behavior of the tannin-based adhesives was successfully determined using FT-IR-ATR spectroscopy in combination with DMTA.

Study of miscibility of melamine-formaldehyde resin and poly(vinyl acetate) blends for use as adhesives in engineered flooring

The objective of this research was to investigate the miscibility behavior of melamine-formaldehyde (MF) resin and poly(vinyl acetate) (PVAc) blends for their use as adhesives for bonding fancy veneer and plywood in engineered flooring, by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). Blends of various compositions of MF resin/PVAc were prepared. To determine and compare the effect of PVAc content, blends with PVAc to MF resin weight ratios of 0, 30, 50, 70 and 100% were prepared. These blends displayed a single cure temperature over the entire range of compositions indicating that this blend system was miscible in the amorphous phase due to the formation of hydrogen bonding between the amine groups of the MF resin and the carbonyl groups of PVAc.

Evaluation of VOC Emissions from Building Finishing Materials Using a Small Chamber and VOC Analyser

A test chamber method was developed to provide a small and simple emission testing facility capable of testing construction products over a range of climatic parameters, such as temperature, ventilation rate and air velocity, that could be varied independently around typical indoor values. Volatile organic compounds (VOCs), specifically the aromatic hydrocarbons fraction, were measured using a “VOC analyser”. This portable measuring equipment is a simple gas-chromatograph which is designed to measure certain aromatic compounds in indoor air. Compounds separated through the column are detected by a semiconductor gas sensor and the concentration of the target compounds automatically calculated and shown. Correlation of the results from this analyser with those from GC/MS was greater than 99%. We have examined the compounds emitted from various building materials, such as medium density fibreboard, particleboard (PB) and wood-based flooring (laminate flooring and engineered flooring), using test methods with a desiccator and 20L small chamber for analysis of VOCs and formaldehyde emission levels. Over 2 and 7 days, we tested the change of VOC emissions with time and compared the results for each material.

Effects of natural-resource-based scavengers on the adhesion properties and formaldehyde emission of engineered flooring

In this study we investigated the effects of using four additives, wheat flour (WF), tannin, rice husk (RH) and charcoal, to melamine-formaldehyde (MF) resin for decorative veneer and base plywood in engineered flooring in order to reduce the formaldehyde emission levels and improve the adhesion properties. We determined the effects of variations in hot-press time, temperature and pressure on the bonding strength and formaldehyde emission. Blends of various MF resin/additive compositions were prepared. To determine and compare the effects of the additives, seven MF resin blends were prepared with the four different additives: four with a wt ratio of 8:2 (MF/WF, MF/tannin, MF/RH and MF/charcoal), and three in the wt ratio of 8:1:1 (MF/WF/tannin, MF/WF/RH and MF/WF/charcoal). The desiccator and perforator methods were used to determine the level of formaldehyde emission. The formaldehyde emission level decreased with all additives, except for RH. At a charcoal addition of only 20%, the formaldehyde emission level was reduced to nearly 0.1 mg/l. Curing of the high WF and tannin content in this adhesive system was well processed, as indicated by the increased lap-shear strength. In the case of WF, the lap shear strength was much lower due to the already high temperature of 130°C. The adhesive layer was broken when exposed to high temperature for extended time. In addition, both WF and tannin showed good mechanical properties. With increasing WF or tannin content, the initial adhesion strength increased. The MF resin samples with 20% added tannin or WF showed both good lap shear and initial adhesion strengths compared to the pure MF resin.

Viscoelastic properties and peel strength of water-borne acrylic PSAs for labels

The use of acrylic emulsion pressure-sensitive adhesives (PSAs) in labels continues to increase due to their environmental friendliness, good aging resistance and excellent processability during coating process. This study has investigated the acrylic emulsion/tackifier blend systems by examining their thermal properties as indicated by the glass transition temperature (T g), by conducting optical microscopy to determine their structure, by exploring their viscoelastic properties with the advanced rheometric expansion system (ARES), and by measuring their peel strength with the 180° peel test. The acrylic emulsion/tackifier blends with low softening point and low molecular weight exhibited only a single T g. However, the acrylic emulsion/tackifier blends with high softening point and high molecular weight showed two T g values. Microscopic observation of blends with miscible tackifier did not show any evidence of tackifier traces, whereas the microscopic structures of blends with immiscible tackifier showed dispersed tackifier particles. As the tackifier content increased, the rubbery plateau region decreased for the miscible blends but increased for the immiscible blends. The 180° peel strength of the miscible blends was dependent on the viscoelastic properties and was influenced by incorporation of tackifiers in the PSA systems. However, the peel strength of the immiscible systems did not depend on the viscoelastic properties at low tackifier content, but it decreased as the tackifier content increased in accordance with the increase of the storage modulus G′.