A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science (Chemistry) May 1993 / One of the greatest environmental drives in the synthetic resins field has been to decrease the formaldehyde emission from cured urea formaldehyde (UF) resins, without adversely affecting their excellent technical performance. [Abbreviated Abstract. Open document to view full version] / MT2017

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Thesis (M.S.)--University of Wisconsin--Madison, 1981. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 107-109).

Urea formaldehyde (UF) resins are widely used as adhesives for wood-based composites. These thermosetting polymers have advantages of relative low price, fast curing speed, and relative good bonding performance. However, UF resin bonded composites are designed for interior applications due to its weak water resistance. Moreover, traditional prevalent ways for recycling wood-based composites face problems caused by UF resins. In this project, the reuse of cured UF resins was systematically studied. The verification and characterization of crystalline structures in cured UF resins were conducted. The results showed that the crystalline regions were accounted for nearly 14.48% in a typical 1.2 formaldehyde to urea (F/U) molar ratio UF resin. The details of the resin crystalline regions, such as grain sizes and interplanar spacing (d-spacing), were characterized. The crystalline structures, nevertheless, did not affect the UF resin hydrothermal hydrolysis in this study. The reuse of cured UF resin was started with a hydrothermal hydrolysis. Under 140 °C and 2 h of hydrothermal process, 20 mL of 30 w.t. % formaldehyde water solution was able to depolymerize up to 1.7 g of cured UF resin. The hydrolyzed formaldehyde solutions were directly used as normal formaldehyde solutions for UF resin synthesis. The synthesized resin (named as UUF resin) contained about 6 w.t. % of cured UF resin and presented similar chemical structures and bonding performance as normal UF resins. Hybrid resins made of UUF resin and polymeric 4-4 diphenyl methane diisocyanate (pMDI) were prepared. The pMDI was found evenly dispersed in the hybrid resins by using acetone as its solvent. These hybrid resins resulted in faster curing and stronger bonding performance than pure UUF resins. Furthermore, the hybrid resin was used in a new bonding design, which used southern pine wood radial section features. This design generated finger joint like bonding interfaces by hot pressing two resin coated wood radial sections. The bonding strength and bond line stability were enhanced by this design.

Formaldehyde emissions from non-structural wood composites are regulated and the regulation target is urea-formaldehyde (UF) resin. UF resins are hydrolytically unstable and constantly emit formaldehyde as a function of temperature and relative humidity. When heated, wood also generates formaldehyde, but this was of little concern until 2010 when formaldehyde regulations became much more demanding. This regulation motivated the industry to account for all formaldehyde sources, synthetic as from resin, and biogenic as from wood. This effort represents first steps towards quantifying biogenic and synthetic contributions to formaldehyde emissions in non-structural wood composites. It is possible to distinguish the 13C/12C isotope ratio of UF resins from the isotope ratio of plant biomass. Conditions during and after composite hot-pressing promote reactions that generate formaldehyde from wood and UF resin, and the kinetic isotope effect continuously lowers the product isotope ratios as a function of yield. If such isotope fractionation did not occur, it would be a simple matter to quantify contributions of wood and UF resin to formaldehyde emissions using static isotope ratios. Isotope fractionation, therefore, complicates the requirements for distinguishing biogenic and synthetic formaldehyde in wood composite emissions. Those requirements are 1) establish the reference carbon isotope ratios in wood and in UF resin (just the formaldehyde portion of UF), and 2) estimate the kinetic isotope effects in formaldehyde generation by wood and cured UF resin. The latter requirement fixes a range for the respective isotope ratios; the numerical ranges enable a simple model of the average isotope ratio for a mixture of biogenic and synthetic formaldehyde in wood composite emissions. Finally, the measured isotope ratio of captured emissions would be compared to the model. This work did not achieve all aspects of the requirements mentioned, but a solid foundation was established for future completion of the ultimate goals. In reference to requirement 1, the carbon isotope ratio of experimental Pinus taeda wood was accurately measured (including some isolated fractions) using isotope ratio mass spectroscopy (IRMS). IRMS of UF resin first requires removal of urea carbons- UF resin was subjected to acid hydrolysis and capture of the resin formaldehyde into aqueous ammonium hydroxide. This provided a nearly quantitative conversion (negligible isotope fractionation) of resin formaldehyde into hexamine for IRMS. Using this hexamine method, the formaldehyde carbon isotope ratios of two industrial UF resins were accurately measured, demonstrating basic feasibility for the project goal. Estimating the kinetic isotope effect (Requirement 2) required creation of a thermochemical reactor, where wood or cured UF resin was heated under N2 flow such that the emitted formaldehyde was easily captured. In this case, conversion of captured formaldehyde into hexamine was abandoned in favor of silica gel cartridges loaded with sodium bisulfite. Isolation and IRMS of the formaldehyde-bisulfite adduct were effective and considered easily transferable to industrial settings. This system was employed to measure fractionation in cured resin as a function of relative humidity, and in Pinus taeda wood as a function of relative humidity, temperature, and time. More information about isotope fractionation is required; but most notable was the fractionation behavior in wood where evidence was found for multiple formaldehyde generating reactions. Overall, this work established feasibility for the goals and laid the foundation for future efforts. / Master of Science / Home-interior products like cabinetry are often produced with wood composites adhesively bonded with urea-formaldehyde (UF) resin. UF resins are low cost and highly effective, but their chemical nature results in formaldehyde emission from the composite. High emissions are avoided, and the federal government has regulated and steadily reduced allowable emissions since 1985. The industry continuously improved UF technologies to meet regulations, as in 2010 when the most demanding regulations were implemented. At that time, many people were unaware that wood also generates formaldehyde; this occurs at very low levels but heating during composite manufacture causes a temporary burst of natural formaldehyde. Some wood types produce unusually high formaldehyde levels, making regulation compliance more difficult. This situation, and the desire to raise public awareness, created a major industrial goal: determine how much formaldehyde emission originates from the resin and how much originates from the wood. These formaldehyde sources can be distinguished by measuring the carbon isotope ratio, 13C/12C. This ratio changes and varies due to the kinetic isotope effect. Slight differences in 13C and 12C reactivity reveal the source as either petrochemical (synthetic formaldehyde) or plant-based (biogenic formaldehyde). This work demonstrates that achieving the industry goal is entirely feasible, and it provides the analytical foundation. The technical strategy is: 1) establish reference isotope ratios in wood and in UF resin, and 2) from the corresponding wood composite, capture formaldehyde emissions, measure the isotope ratio, and simply calculate the percentage contributions from the reference sources. However, a complication exists. When the reference sources generate formaldehyde, the respective isotope ratios change systematically in a process called isotope fractionation (another term for the kinetic isotope effect). Consequently, this effort developed methods to measure fractionation when cured UF resin and wood separately generate formaldehyde, with greater emphasis on wood. Isotope fractionation in wood revealed multiple fractionation mechanisms. This complexity presents intriguing possibilities for new perspectives on formaldehyde emission from wood and cured UF resin. In summary, this work demonstrated how source contributions to formaldehyde emissions can be determined; it established effective methods required to refine and perfect the approach, and it revealed that isotope fractionation could serve as an entirely novel tool in the materials science of wood composites.

Submitted by RAFAEL AUGUSTO PINHOLATI EUGENIO null (rafael.pinholati@duratex.com.br) on 2016-12-06T23:33:20Z No. of bitstreams: 1 DISSERTAÇÃO RAFAEL - MESTRADO Rev 4.pdf: 3957807 bytes, checksum: 74c157bc6d300c719cca57459b4455da (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-12-09T12:54:47Z (GMT) No. of bitstreams: 1 eugenio_rap_me_bauru.pdf: 3957807 bytes, checksum: 74c157bc6d300c719cca57459b4455da (MD5) / Made available in DSpace on 2016-12-09T12:54:47Z (GMT). No. of bitstreams: 1 eugenio_rap_me_bauru.pdf: 3957807 bytes, checksum: 74c157bc6d300c719cca57459b4455da (MD5) Previous issue date: 2016-12-02 / O trabalho consistiu na produção de painéis de MDF (Medium Density Fiberboard) em escala laboratorial utilizando o adesivo PVA (Poliacetato de Vinila), variando suas concentrações e realizando misturas com a resina comumente empregada neste processo, o adesivo a base de uréia-fomaldeído, onde foi avaliado além das características físicas e mecânicas dos painéis produzidos, também teve o intuito de verificar o desprendimento de formaldeído para o ambiente quando aplicado juntamente com a resina uréia-fomaldeído, e a avaliação dos perfis de densidades dos traços. As amostras foram confeccionadas com fibra de eucalipto, onde as dosagens do adesivo PVA seguiram as seguintes proporções: 30%, 50% e 70%, e para efeito de comparação com as amostras produzidas com a mistura de PVA foram fabricadas provas em branco com 100% uréia-formaldeído. No total foram produzidas 16 amostras, quatro painéis de cada traço, e retirados os corpos de prova que posteriormente foram avaliados conforme a NBR 15316-2:2015 para as condições secas. Todos os insumos foram fornecidos pelo fabricante de painéis Duratex SA, e os testes foram realizados nos laboratórios da empresa. O adesivo PVA mostrou-se bastante favorável, apresentando grande compatibilidade com os demais componentes da formulação, apresentando potencial para fabricação de MDF. Diversos traços conseguiram atender os requisitos da norma, com destaque para módulo de ruptura (MOR), módulo de elasticidade (MOE), obtidos atraves do ensaio de flexão estática, e o teor de umidade. Houve também uma discreta redução na emissão de formol em dois traços (T3 e T4), e na avaliação dos perfis de densidade foi constatado que a formulação dos traços não impactou nas densidades médias da espessura dos painéis. / The work consisted in the production of MDF (Medium Density Fiberboard) in laboratory scale using PVA adhesive (Polyacetate Vinyl Chloride), varying their concentrations and performing mixtures with commonly used resin in this process, the adhesive base of ureafomaldehyde, which was evaluated in addition to the physical and mechanical characteristics of the panels produced, also aimed to check the formaldehyde release to the environment when applied together with resin urea-fomaldehyde, and evaluation of the densities of the features profiles. The samples were made from eucalyptus fibers where PVA adhesive doses followed the following proportions: 30%, 50% and 70%, and for the purpose of comparison with the samples produced with the mixture of PVA blank tests were made with 100 % ureaformaldehyde. In total, we produced 16 samples, four panels of each stroke, and removed the specimens which were then evaluated according to NBR 15316-2: 2015 for dry conditions. All inputs were provided by the panel manufacturer Duratex SA, and the tests were performed in the company's laboratories. PVA adhesive proved to be very favorable, with high compatibility with the other components of the formulation, with potential for the production of MDF. Many features were able to meet the standard requirements, particularly modulus of rupture (MOR), modulus of elasticity (MOE), obtained through the bending, and moisture content test. There was also a slight reduction in formaldehyde emissions by two dashes (T3 and T4), and evaluation of density profiles was found that the formulation of the traits did not affect the average thickness of the thickness of the panels.

In this study, a series of denim fiberboards are fabricated using two different resins, malamine urea formaldehyde (MUF) and polymeric methylene diphenyl diisocyanate (pMDI). Two experimental design factors (1) adhesive content and (2) MUF-pMDI weight ratio, were studied. All the denim fiberboard samples were fabricated following the same resin blending, cold-press and hot-press procedures. The physical and mechanical tests were conducted on the fiberboard following the procedures described in ASTM D1037 to obtain such as modulus of elasticity (MOE), modulus of rupture (MOR), internal bond (IB), thickness swell (TS), and water absorption (WA). The results indicated that the MOE was significantly affected by both factors. IB was affected significantly by weight ratio of different glue types, with 17 wt% more MDI resin portion in the core layer of the denim boards, the IB for total adhesive content 15% fiberboard was enhanced by 306%, while for total adhesive content 25% fiberboard, enhanced by 205%. TS and WA, with higher adhesive content used in denim boards' fabrication, and more pMDI portion in the core layer of the boards, the boards' TS and WA was reduced by up to 64.2% and 78.8%, respectively.

The objective of this study was to investigate the effects of melamine and ether contents on the curing and performance properties of UF resins as binders for wood composites. Various UF and UMF resins were synthesized with three different synthesis procedures. These resins were examined by 13C NMR, rheometer, and other methods and evaluated as particleboard binders. Three-layer particleboards were prepared with the resins catalyzed with various catalysts and levels, applied in face and core layers. The board test results were compared. Only about half of added melamine had reacted with formaldehyde. UMF resins were found to be catalyzed with stronger catalysts at suitable levels depending on melamine levels and on which layer of particleboard the UMF resins are to be applied. Even catalyzed with a stronger catalyst, the curing rates of UMF resins were still slower, and storage stabilities were shorter than UF resins, but the pot lives were longer, and internal bond strength and water resistance were higher. Moreover, resins synthesized with procedures 2 and 3 showed obviously longer storage times, longer pot lives, and longer gel times, and the particleboards bonded with these resins showed significant improvements in internal bond strength and water absorption values but the formaldehyde contents increased. The increased formaldehyde content test values indicated that linear methylene-ether groups in UF resins decompose in the hot-pressing of boards to emit formaldehyde, most of which is not captured back into the UF resin matrix. Uron-type methylene-ether groups decompose in the hot-pressing of boards to participate in the curing process and enhance the bonding of boards, but it could also emit extra formaldehyde which may not be effectively captured by UF resins but more effectively by UMF resins if the amount of melamine is high enough because of the increased reactive capacities of melamine. The results of this research offered a new hypothesis that the linear methyleneether bonds in UF resins might be a major contributor of the high free formaldehyde contents of particleboards. Decreasing the linear methylene-ether groups contents might effectively bring down the formaldehyde content of boards.

Thesis (PhD (Chemistry and Polymer Science)--University of Stellenbosch, 2009. / The work presented in this dissertation describes the development of self-healing coatings based on thiol-ene chemistry. The approach was to synthesize capsules with thiol and ene compounds separately encapsulated. These capsules were embedded in various coating formulations and upon the formation of a crack with a razor blade, these capsules ruptured. This caused the healing agent to flow into the crack via capillary action and the thiol-ene healing mechanism was initiated. This resulted in recovery of the damaged coating and provided continued protection to the substrate. Pentaerythritol tetrakis(3-mercaptopropionate) (TetraThiol), 1,6-hexanediol diacrylate (DiAcrylate) and 1,6-hexanediol di-(endo, exo-norborn-2-ene-5-carboxylate) (DiNorbornene) are the thiol and ene compounds used in this study. Kinetic experiments indicated that both TetraThiol-DiAcrylate and TetraThiol-DiNorbornene monomer pairs undergo rapid polymerization and form a network within minutes upon exposure to UV radiation and with the addition of a photoinitiator. The TetraThiol-DiNorbornene monomer pair also showed a high rate of polymerization without the addition of a photoinitiator and/or exposure to UV radiation. Styrene-maleic anhydride (SMA) copolymers and chain-extended block copolymers with styrene (P[(Sty-alt-MAh)-b-Sty]) were synthesized via Reversible Addition-Fragmentation chain Transfer (RAFT)- mediated polymerization. These copolymers were used as surfactant in miniemulsification for the synthesis of core-shell particles with TetraThiol as the core material. It appeared that P[(Sty-alt-MAh)-b-Sty] block copolymers, sterically stabilized via the addition of formaldehyde, provide optimal stability to the core-shell particles. DiNorbornene is encapsulated via miniemulsion homopolymerization of styrene and well-defined, stable nanocapsules were obtained. TetraThiol and DiAcrylate microcapsules were synthesized via in-situ polymerization of urea and formaldehyde. Microcapsules with a particle size of one to ten micrometers and with a very smooth surface were obtained. These microcapsules and nanocapsules were embedded in poly(methyl acrylate) (PMA), styrene-acrylate and pure acrylic films and the self-healing ability of these coatings, after introduction of a crack with a razor blade, was assessed.

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