Non-isothermal and isothermal thermomechanical analysis (TMA) of the cross-linking and hardening of wood joints bonded with urea-formaldehyde (UF), melamine-urea-formaldehyde (MUF), and phenol-melamine-urea-formaldehyde (PMUF) resins was carried out, allowing the determination of the variation of physical properties of these thermosetting adhesives in situ in the wood joint. Gelling temperature, hardening and vitrification temperature and temperature at which relative elastic moduli reach their maximum were also determined for wood joints obtained with the three resins. Deductions as regards rates of hardening, influence of amount of hardener and of curing temperature are reported on the basis of the measured TMA variation of the relative elastic moduli of the joints assemblies.

The adsorption properties of clay minerals (e.g. montmorillonite and palygorskite) have been improved through chemical treatment methods. However, the addition of extra chemicals is often not friendly to the environment and powdered clay-mineral adsorbents are inconvenient for some applications. To overcome these drawbacks in the present study, granular montmorillonite-palygorskite adsorbents (GMPA) were successfully prepared using Na-alginate and thermal treatments to improve heavy metal removal from water. The properties of GMPA samples under different calcination temperatures were examined using thermogravimetric (TG) analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), and specific surface area (BET). The results indicated that loss of mass by GMPA relative to the untreated montmorillonite-palygorskite was due to the loss of water, adsorbed Na-alginate, and mineral decomposition during thermal treatment. Changes in the morphology and crystallinity were significant at calcination temperatures from 500°C to 1000°C. The layered morphology totally disappeared after calcination at 1000°C, while transformation of the montmorillonite and palygorskite to a non-crystalline material was almost complete at 800°C and new crystalline phases appeared. Calcination temperature had a significant influence on the specific surface areas and pore volumes of GMPA. Both the changes in texture and chemical structure affected Pb2+ and Cu2+ removal. The GMPA sample produced at a 600°C calcination temperature was the most promising adsorbent for heavy metal removal from water.

ABSTRACT:The dependence on the temperature of the state of a highly crosslinked polymer network can be modeled as a function of well-defined molecular-level network parameters to yield a simple applied model equation. The tightness and strength (modulus of elasticity) of the crosslinked networks formed, as well as any further tightening of the network due to further curing, can easily be compared with the parameters A, M, and ␣ (the coefficient of branching) and the m/E ratio and, therefore, with parameters directly related to molecular-level characteristics of the system. The crosslinking contribution to the network is represented by A and M, the former representing the frequency of crosslinking and the latter having the dimensions of an energy. The ratio m/E, that is, the ratio of the average number of degrees of freedom of chain segments between crosslinking nodes (m) to the average energy of nonbonded atom interactions between the same segments (E), and ␣ model the noncrosslinked contribution to the characteristics of the network. These are the same parameters that appear in the simple equation modeling the dependence of the characteristics of the network on the temperature within a limited temperature range.

Trimethylolpropane triacrylate (TMPTA) resin was cured under UV radiation, with 2,2-dimethoxy-2-phenylacetophenon (DMPA) and a mixture of benzophenone and methyl-diethanolamine (BP/MDEA) as initiators and three phenolic compounds as inhibitors, respectively. For each formulation, the curing enthalpy was measured by photocalorimetry and the modulus of elasticity (MOE) of cured resin films by thermomechanical analysis. The DMPA resulted in networks with higher rigidity that was slightly reduced by the addition of a phenolic compound; while the networks were more flexible and the effects in reducing the MOE by the phenols were much more pronounced when the BP/MDEA was used as an initiator. For the three phenolic compounds, their importance in reducing the MOE can be ranked in the order of eugenol Ͼ dimethoxyphenol Ͼ phenol. Three equations are proposed to model the structureproperty relationship of TMPTA networks. These models suggest that 1) the MOE increases with the crosslinking density, which is proportional to the conversion degree to a power of about 1/3, indicating that cyclization becomes progressively more important as the photopolymerization advances; 2) the decrease of the MOE with temperature is mainly due to relaxation of pending chains and chain segments, and the activation energy needed to overcome such an energy barrier is greater for a less crosslinked network than for a more crosslinked one; and 3) the overall contribution of the crosslinking and the interactions between pending chains (secondary forces) can be expressed by a simple equation in which the network rigidity (MOE) is a function of the degree of conversion, the activation energy and the temperature.

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