Impact of alkaline–acid and strongly acid process on the synthesis of urea–formaldehyde resins and derived composites: a comparison study

Gonçalves, Cláudia; Pereira, João; Almeida, Margarida; Paiva, Nádia; Ferra, João; Martins, Jorge; Magalhães, Fernão D.; Barros‐Timmons, Ana; Carvalho, Luísa

doi:10.1007/s00107-019-01453-4

Cited by 4 publications

(5 citation statements)

References 23 publications

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“…The differences between the syntheses were mainly based on different formaldehyde/urea molar ratios during the synthesis, temperatures, and the number of urea additions. The resins differed in some characteristics, namely percentage of unreacted oligomers, chemical composition, viscosity, and reactivity [152]. The internal bonds of the particleboards bonded with them was similar for all the resins prepared with the alkaline-acid process, but were better than those bonded with the strong acid step; nonetheless, formaldehyde emission appeared to be independent of the type of synthesis used.…”

Section: New Approaches To Synthetic Adhesivesmentioning

confidence: 97%

“…Not all can be presented here, but a few of the more interesting examples are selected. There are two distinct trends in this context: (i) the ongoing improvement, also considerable, of traditional synthetic adhesives, especially in UF resins with, moreover, very valuable new ideas being presented [150][151][152][153][154][155][156] and MUF resins (see later), and (ii) the presentation of partially non-traditional or even totally non-traditional synthetic adhesives, some also with biobased content.…”

Section: New Approaches To Synthetic Adhesivesmentioning

confidence: 99%

“…Equally, mixing a uron-rich resin with a low F/U molar ratio UF resin yielded resins of greater strength than a simple UF of corresponding molar ratio, indicating that UF resins of lower formaldehyde emission with still acceptable strength could be prepared with these resins [151]. Subsequent research on this aspect compared five resins produced in different manners: four via the traditional alkaline-acid process and one using the strongly acid step process [152]. The differences between the syntheses were mainly based on different formaldehyde/urea molar ratios during the synthesis, temperatures, and the number of urea additions.…”

Section: New Approaches To Synthetic Adhesivesmentioning

confidence: 99%

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Wood Composites and Their Polymer Binders

2020

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This review presents first, rather succinctly, what are the important points to look out for when preparing good wood composites, the main types of wood composites manufactured industrially, and the mainly oil-derived wood composite adhesives and binders that dominate and have been dominating this industry. Also briefly described are the most characteristic biosourced, renewable-derived adhesives that are actively researched as substitutes. For all these adhesives, synthetic and biosourced, the reviews expose the considerable progresses which have occurred relatively recently, with a host of new approaches and ideas having been proposed and tested, some even implemented, but with even many more already appearing on the horizon.

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Section: New Approaches To Synthetic Adhesivesmentioning

confidence: 97%

Section: New Approaches To Synthetic Adhesivesmentioning

confidence: 99%

Section: New Approaches To Synthetic Adhesivesmentioning

confidence: 99%

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Wood Composites and Their Polymer Binders

2020

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“…Even when comparing with wood-based particleboards produced with synthetic adhesives, the results are remarkable. Pine wood particleboards bounded with urea-formaldehyde resins reported in the literature present thickness swelling values between 27% and 38% [35,36].…”

Section: Effect Of Starch/cardoon Ratiomentioning

confidence: 99%

Low-Density Cardoon (Cynara cardunculus L.) Particleboards Bound with Potato Starch-Based Adhesive

et al. 2020

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In the present work, and for the first time, totally biosourced low-density particleboards were produced using cardoon particles (a no added value by-product from the Portuguese cheese making industry), bound with a potato starch adhesive. Different starch/cardoon ratios (0.6, 0.8, 1 and 1.2) were tested and the effect of different bio-based additives (chitosan, wood fiber and glycerol) on the performance of the adhesive system was evaluated. The best result was obtained for a formulation with a starch/cardoon mass ratio of 0.8, a chitosan/starch mass ratio of 0.05 and a water/starch mass ratio of 1.75. The particleboards produced had a density of 323 kg·m−3, internal bond strength of 0.35 N·mm−2 and thickness swelling of 15.2%. The values of density and internal bond strength meet the standard requirements of general-purpose lightweight boards for use in dry conditions according to CEN/TS 16368 specification. Moreover, the susceptibility of the formulations with best results was established against subterranean termites and one decay fungi.

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“…On the other hand acid catalyst enhanced the formation of methylene, ether linkages, and urons. Gonçalves et al reported that degree of condensation is higher on the alkaline-acidic combined process than only strong acid catalyze stage [18].…”

Section: Introductionmentioning

confidence: 99%

Effect of Synthesis Conditions on the Molecular Weight and Activation Energy of Urea-formaldehyde Prepolymer and Their Relationship

Anjum

Khan

2020

JEA

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The aim of this study is to find out the viscosity change of urea-formaldehyde (UF) resin with the synthesis parameters namely formaldehyde/urea (F/U) mole ratios, pH and temperature. The viscosity of UF resins, related to molecular weight and activation energy is very important factor of their usability. Urea-formaldehyde (UF) prepolymer was synthesized through polycondensation reaction with F/U ratio 0.8, 1.0, 1.2, 1.4, 1.6. The synthesis was carried out by two steps: alkali catalysis at reaction pH 8.3, 90°C for 60 min and thereafter acid catalysis at pH 4.3, 83°C for 15 min. Viscosity of prepolymer was determined at acid catalysis step by simple glass viscometer. Weight average molecular weight (Mw) was calculated from the viscosity data of UF prepolymer using Mark-Houwink equation. Highest Mw (2020.9) of prepolymer was obtained at F/U molar ratio 1.0 and pH 4.3. In addition, it was found that pH 4.0 yielded greater Mw (2049) UF prepolymer among the four reactions which were performed at pH 4.0, 4.3, 4.7, and 5.0. The energy of activation (Ea) of UF prepolymer was also calculated from the measured viscosity at temperature 70, 75, 80 and 85°C. The highest values of Ea were also found at F/U molar ratio 1.0 and pH 4.0 & lowest values was obtained at F/U molar ratio 1.6 and pH 5.0. From the experimental data, it was shown that the values of Ea and Mw were varied comparably with the change of reaction parameters.

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Impact of alkaline–acid and strongly acid process on the synthesis of urea–formaldehyde resins and derived composites: a comparison study

Cited by 4 publications

References 23 publications

Wood Composites and Their Polymer Binders

Wood Composites and Their Polymer Binders

Low-Density Cardoon (Cynara cardunculus L.) Particleboards Bound with Potato Starch-Based Adhesive

Effect of Synthesis Conditions on the Molecular Weight and Activation Energy of Urea-formaldehyde Prepolymer and Their Relationship

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