title: Studies of the formation and properties of urea-formaldehyde resin adhesives

authors: Zeng, Huiyang

abstract: Urea-formaldehyde (UF) resin is used primarily as an adhesive for manufacturing wood panels (medium density fiberboard, particleboard and plywood). These are important New Zealand export products. A better understanding of the formation of UF resin will allow maximisation of its adhesive properties (high bonding strength) and minimisation of formaldehyde emissions (an adverse environmental effect). These improvements will enhance the competitive advantage of New Zealand resin products.

The research reported here has been directed primarily towards monitoring the UF reaction by Nuclear Magnetic Resonance spectroscopy (NMR), preparing UF resins, determining the performance of the resins produced and characterising the resins by high performance liquid chromatography (HPLC), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) methods.

The development of a dynamic (RAPID) NMR acquisition method has contributed to the identification of optimum conditions for UF resin manufacture. A series of NMR "snap-shots" of the UF reaction system over the entire reaction period has been obtained. A wide range of reaction conditions, eg formaldehyde to urea molar ratio, formaldehyde concentration, initial addition pH, condensation pH, addition reaction time and reaction temperature, have been investigated. From the species present and the changes in their relative concentrations during the reaction, optimum reaction conditions have been determined as:

Formaldehyde concentration: 35-46%
F/U molar ratio: 1.8-2.0
Temperature: 88°C
Addition reaction time: 25-30 min
Initial addition pH: 8.0-9.0
Condensation pH: 4.5-5.0

The dynamic (RAPID) NMR studies were complemented by HPLC characterisation of samples taken during the different reaction stages. The main low molecular weight species present in the UF reaction system have been identified. In general the HPLC results were consistent with those obtained by the dynamic (RAPID) NMR method.

Low molecular weight species were identified by electrospray mass spectrometry.

Molecular weight, molecular weight distribution and resin aging were investigated by the GPC method. The number average molecular weights of typical final UF resins were in the range of 600-800 Dalton. The weight average molecular weights of the same resins were in the range of 7000-10 000 Dalton.
A series of laboratory resins were prepared to test the appropriateness of the optimum reaction conditions predicted from the NMR and HPLC studies. Resin performance in wood panels was determined by measuring internal bond, formaldehyde emission and cold water swell. The effects of F/U molar ratio, resin loading and board thickness on the panel properties have also been determined. The results showed improvement in the internal bond and formaldehyde emissions.

Comparison of the experimental resin prepared under the optimum reactions with a commercial unmodified UF resin indicated that a 12% increase in internal bond. Formaldehyde emissions were similar.

It is clear from the results of this study that current manufacturing conditions for the production of unmodified UF resins are close to optimum. Future improvements are likely to be based upon structural and/or non-structural additives.

text: Studies of the formation and properties of urea-formaldehyde resin adhesives Urea-formaldehyde (UF) resin is used primarily as an adhesive for manufacturing wood panels (medium density fiberboard, particleboard and plywood). These are important New Zealand export products. A better understanding of the formation of UF resin will allow maximisation of its adhesive properties (high bonding strength) and minimisation of formaldehyde emissions (an adverse environmental effect). These improvements will enhance the competitive advantage of New Zealand resin products.

The research reported here has been directed primarily towards monitoring the UF reaction by Nuclear Magnetic Resonance spectroscopy (NMR), preparing UF resins, determining the performance of the resins produced and characterising the resins by high performance liquid chromatography (HPLC), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) methods.

The development of a dynamic (RAPID) NMR acquisition method has contributed to the identification of optimum conditions for UF resin manufacture. A series of NMR "snap-shots" of the UF reaction system over the entire reaction period has been obtained. A wide range of reaction conditions, eg formaldehyde to urea molar ratio, formaldehyde concentration, initial addition pH, condensation pH, addition reaction time and reaction temperature, have been investigated. From the species present and the changes in their relative concentrations during the reaction, optimum reaction conditions have been determined as:

Formaldehyde concentration: 35-46%
F/U molar ratio: 1.8-2.0
Temperature: 88°C
Addition reaction time: 25-30 min
Initial addition pH: 8.0-9.0
Condensation pH: 4.5-5.0

The dynamic (RAPID) NMR studies were complemented by HPLC characterisation of samples taken during the different reaction stages. The main low molecular weight species present in the UF reaction system have been identified. In general the HPLC results were consistent with those obtained by the dynamic (RAPID) NMR method.

Low molecular weight species were identified by electrospray mass spectrometry.

Molecular weight, molecular weight distribution and resin aging were investigated by the GPC method. The number average molecular weights of typical final UF resins were in the range of 600-800 Dalton. The weight average molecular weights of the same resins were in the range of 7000-10 000 Dalton.
A series of laboratory resins were prepared to test the appropriateness of the optimum reaction conditions predicted from the NMR and HPLC studies. Resin performance in wood panels was determined by measuring internal bond, formaldehyde emission and cold water swell. The effects of F/U molar ratio, resin loading and board thickness on the panel properties have also been determined. The results showed improvement in the internal bond and formaldehyde emissions.

Comparison of the experimental resin prepared under the optimum reactions with a commercial unmodified UF resin indicated that a 12% increase in internal bond. Formaldehyde emissions were similar.

It is clear from the results of this study that current manufacturing conditions for the production of unmodified UF resins are close to optimum. Future improvements are likely to be based upon structural and/or non-structural additives.

year: 2001

title: The effect of SDS and TEG on chain mobility and secondary structure of decolored bloodmeal

authors: Hicks, Talia

subjects: IR spectroscopy

abstract: The effect of sodium dodecyl sulfate (SDS) and triethylene glycol (TEG) on secondary structure of decolored bloodmeal (DBM) during heating was examined via synchrotron-based Fourier transform infra-red spectroscopy (FT-IR) and wide angle X-ray scattering (WAXS). Both additives homogenize secondary structure distribution; SDS increases α-helices and decreases β-sheets and β-turns, while SDS–TEG reduces α-helices and β-sheets and increase random coils. Short heat cycles only change the composition of SDS-TEG treated DBM, implying TEG is responsible for chain mobility. Prolonged heating slowly increases β-sheets and suddenly increases α-helices at 55–75 °C in SDS-TEG treated DBM and 100 °C in SDS-treated DBM. Finally, WAXS shows that structural change due to heating is reversible for SDS-TEG treated DBM

text: The effect of SDS and TEG on chain mobility and secondary structure of decolored bloodmeal The effect of sodium dodecyl sulfate (SDS) and triethylene glycol (TEG) on secondary structure of decolored bloodmeal (DBM) during heating was examined via synchrotron-based Fourier transform infra-red spectroscopy (FT-IR) and wide angle X-ray scattering (WAXS). Both additives homogenize secondary structure distribution; SDS increases α-helices and decreases β-sheets and β-turns, while SDS–TEG reduces α-helices and β-sheets and increase random coils. Short heat cycles only change the composition of SDS-TEG treated DBM, implying TEG is responsible for chain mobility. Prolonged heating slowly increases β-sheets and suddenly increases α-helices at 55–75 °C in SDS-TEG treated DBM and 100 °C in SDS-treated DBM. Finally, WAXS shows that structural change due to heating is reversible for SDS-TEG treated DBM

year: 2014-11

title: Are we really colour-blind? The normalisation of mass female incarceration

authors: Norris, Adele N.

abstract: The sharp rise in female incarceration rates in both the United States and New Zealand has received increased attention. Even more pressing are the racial disparities among imprisoned females. This exploratory case study examines 13 peer-reviewed articles published between 2005 and 2016 to understand the nature of colour-blind ideology in discussions of female imprisonment in New Zealand. Several themes emerged including the homogenisation of female prisoners. Apart from moderately linking vast racial disparities between incarcerated White women and Indigenous women to ill-defined colonial practices, contemporary explanations for the substantial racial disparities receive little attention. This article concludes that the absence of a critical lens toward contemporary forms and experiences of racism undergirding the mass criminalisation of Indigenous people perpetuates a colour blindness that in turn works to normalise mass female incarceration. Even in attempts to be unbiased, the way race/ethnicity, gender, age, and class are discussed in academic research exploring female incarceration seems to reflect the influential nature of controlling images rather than critique them.

text: Are we really colour-blind? The normalisation of mass female incarceration The sharp rise in female incarceration rates in both the United States and New Zealand has received increased attention. Even more pressing are the racial disparities among imprisoned females. This exploratory case study examines 13 peer-reviewed articles published between 2005 and 2016 to understand the nature of colour-blind ideology in discussions of female imprisonment in New Zealand. Several themes emerged including the homogenisation of female prisoners. Apart from moderately linking vast racial disparities between incarcerated White women and Indigenous women to ill-defined colonial practices, contemporary explanations for the substantial racial disparities receive little attention. This article concludes that the absence of a critical lens toward contemporary forms and experiences of racism undergirding the mass criminalisation of Indigenous people perpetuates a colour blindness that in turn works to normalise mass female incarceration. Even in attempts to be unbiased, the way race/ethnicity, gender, age, and class are discussed in academic research exploring female incarceration seems to reflect the influential nature of controlling images rather than critique them.

year: 2017