RESUMO
The global production of plywood is constantly increasing as its application in the furniture and interior decoration industry becomes more widespread. An urgent issue is how to decrease the formaldehyde released from plywood, considering its carcinogenic effect on humans and harm to the environment. Reducing the free formaldehyde content of the urea formaldehyde (UF) adhesives used in the preparation process is considered an effective method. Therefore, it is necessary to identify a new type of formaldehyde scavengers. Here, the strongly reducing substance sodium borohydride was used to reduce and degrade the free formaldehyde in UF adhesives, and its effects on the properties of the UF adhesive and plywood were studied. When 0.7% sodium borohydride was added to the UF adhesive with a molar ratio of formaldehyde to urea of 1.4:1, the free formaldehyde content of the UF resin decreased to 0.21%, which is 53% lower than that of the untreated control. Moreover, the formaldehyde released from the plywood was reduced to 0.81 mg/L, ~45% lower than that from the group. The bonding strength of the treated samples could reach ~1.1 MPa, which was only reduced by ~4% compared to that of the control. This study of removing formaldehyde from UF adhesive by reduction could provide a new approach for suppressing formaldehyde release from the final products.
RESUMO
A novel type of phenol-formaldehyde (PF) resin was prepared by utilizing the liquefaction products liquefied by phenol under acidic conditions and then reacted with formaldehyde under alkaline conditions. The relationship between the liquefaction behavior of cassava starch and the properties of modified PF resin wood adhesive was studied. The effects of the liquid-solid ratio of phenol to cassava starch, sulfuric acid usage, and liquefaction time on the liquefaction residue rate and relative crystallinity of cassava starch were determined. The results showed that the bonding strength of modified PF resin decreased gradually with the decrease of the liquid-solid ratio. It was a great surprise that bonding strength still met the requirement of the national standard of 0.7 MPa when the liquid-solid ratio was 1.0. The detailed contents were analyzed through FT-IR, SEM, and XRD. In terms of the utilization of bio-materials for liquefaction to synthesize wood adhesive, cassava starch may be superior to the others.
RESUMO
The purpose of this work is to investigate the effects of copper (II) sulfate on the formaldehyde release and the mechanical properties of urea formaldehyde (UF) adhesive. Copper (II) sulfate has been used as a formaldehyde scavenger in UF resin, and its effects on the physical and chemical properties of UF adhesive have been studied. Moreover, the mechanical properties and formaldehyde release of plywood prepared with modified UF resin have been determined. The UF resin has been characterized by Fourier-transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). FTIR spectra showed that the addition of copper (II) sulfate to the UF resin does not affect the IR absorptions of its functional groups, implying that the structure of UF is not modified. Further results showed that the free formaldehyde content of the UF resin incorporating 3% copper (II) sulfate was 0.13 wt.%, around 71% lower than that of the untreated control UF adhesive. With a copper (II) sulfate content of 3%, the formaldehyde release from treated plywood was 0.74 mg·L-1, around 50% lower than that from the control UF adhesive, and the bonding strength reached 1.73 MPa, around 43% higher than that of the control.
RESUMO
The rate of intramolecular charge transfer from biphenyl to naphthalene was determined for the radical anions and radical cations of molecules with the general structure: (2-naphthyl)-(steroid spacer)-(4-biphenylyl). Varied degrees of unsaturation (one double bond, NSenB; two double bonds, NSen(2)B; and the b-ring completely aromatized, NSarB) were incorporated into the steroid spacer to examine the effect it would have on the charge transfer rate. The charge transfer rate, as inferred from the decay of the biphenyl radical ion absorption, increased in all cases relative to the completely saturated 3-(2-naphthyl)-16-(4-biphenylyl)-5alpha-androstane (NSB) reference molecule. For the anion charge transfer, the decay rates increased by factors of 1.4, 4.2, and 5.1, respectively, and for the cation, the decay rates increased by factors of 5, 276, and 470. To explain the results, the charge-transfer process was viewed as a combination of two independent mechanisms: a single-step, superexchange mechanism, and a two-step, sequential charge transfer. Using a low level of theory, simple models of the superexchange and two-step mechanisms were developed to elucidate the nature and differences between the two mechanisms. The critical variable for this analysis is the free energy of formation (DeltaG(I) degrees ) of the intermediate state: (2-naphthyl)-[spacer](1)+/--(4-biphenylyl). The conclusion from this treatment is that superexchange is the dominant mechanism when DeltaG(I) degrees is large, but at small DeltaG(I) degrees , the sequential mechanism will dominate. This is because the superexchange rate is shown to have a weak dependence on DeltaG(I) degrees , changing 10-fold for a change in DeltaG(I) degrees of 2 eV, compared to the sequential mechanism in which the rate can change over 10(3) for 0.5 V.
