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Sacarose como substituto da melamina em resinas de melamina-ureia-formaldeído
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O presente trabalho teve como principal objetivo avaliar o potencial da sacarose como
substituto parcial ou total da melamina na formulação de resinas melamina-ureia-formaldeído
(mUF), utilizadas como adesivos na produção de painéis de partículas de madeira. Esta
abordagem surge na sequência da recente classificação da melamina como substância de
elevada preocupação, incentivando o desenvolvimento de alternativas mais sustentáveis e
seguras.
No âmbito deste estudo, foram produzidas nove resinas: uma através do processo fortemente
ácido (UF-1) e sete através do processo alcalino–ácido (UF-2 a UF-8), incluindo ainda uma resina
standard (STD), que serviu de referência para avaliar o desempenho das restantes como
sistemas adesivos para a produção de painéis que devem obedecer aos requisitos da norma NP
EN 312:2010.
Foram exploradas 2 estratégias principais de incorporação da sacarose. A 1ª consistiu no
processo fortemente ácido através da incorporação da sacarose. Esta abordagem resultou num
desempenho mecânico inferior, com valores de resistência interna (IB) de 0,22 N/mm² (face a
0,39 N/mm² da resina STD) e maior inchamento (51,3 % face a 38,7 %).
Ao contrário do processo fortemente ácido, a segunda abordagem baseou-se no processo
alcalino-ácido no qual se incorporou diretamente sacarose ou um sistema com aditivo (A1 e A2).
Estes aditivos foram formulados a partir de sacarose, à qual se associou o componente 1 no
caso do aditivo A1, e os componentes 1 e 2 no caso do aditivo A2. Esta abordagem, permitiu
melhorar o desempenho relativamente ao processo fortemente ácido. No entanto, os valores
do IB a obtidos com a incorporação direta da sacarose e com o A1 permaneceram inferiores aos
da resina STD e o inchamento superior ao da resina STD. Dentro desta estratégia, destacou-se
a utilização do aditivo A2, evidenciando que o componente 2 desempenha um papel relevante
na promoção da formação de espécies intermédias reativas e na melhoria da estrutura da rede
polimérica. Verificou-se, contudo, que o desempenho das resinas depende de forma
significativa das condições de síntese, nomeadamente da concentração do aditivo e do
momento da sua incorporação. Neste contexto, a resina UF-7 apresentou o melhor
desempenho global, com incorporação de 0,5 % de aditivo após a 1ª adição de ureia. Esta
formulação evidenciou valores de IB (0,40 N/mm²) próximos dos da resina STD e menor
inchamento (36,6 %), indicando uma melhoria na estabilidade dimensional. Em contrapartida,
apresentou um teor de formaldeído emitido superior (3,90 mg/m²h face a 3,60 mg/m²h),
associado a uma maior razão molar formaldeído/ureia.
Desta forma, os resultados demonstram que a sacarose, particularmente quando combinada
com o componente 2 e integrada em estratégias de síntese adequadas, apresenta potencial
para substituir a melamina em resinas adesivas, contribuindo para o desenvolvimento de
sistemas mais sustentáveis.
The main objective of this work was to evaluate the potential of sucrose as a partial or total substitute for melamine in the formulation of melamine-urea-formaldehyde resins (mUF), used as adhesives in the production of wood particleboards. This approach arises from the recent classification of melamine as a substance of very high concern, encouraging the development of more sustainable and safer alternatives. Within the scope of this study, nine resins were produced: one through a strongly acidic process (UF-1) and seven through an alkaline–acid process (UF-2 to UF-8), as well as a standard (STD) resin, which was used as a reference to evaluate the performance of the others as adhesive systems for panel production, in accordance with the requirements of NP EN 312:2010. Two main sucrose incorporation strategies were investigated. The first consisted of incorporating sucrose into a strongly acidic synthesis process. This approach resulted in poorer mechanical performance, with an internal bond (IB) value of 0,22 N/mm² (compared to 0,39 N/mm² for the STD resin) and higher thickness swelling (51,3 % compared to 38,7 %). In contrast to the strongly acidic process, the second approach was based on the alkaline–acid process, in which either sucrose or an additive system (A1 and A2) was directly incorporated. These additives were formulated from sucrose combined with component 1 in the case of additive A1, and with components 1 and 2 in the case of additive A2. This approach led to improved performance compared to the strongly acidic process. However, the IB values obtained with direct sucrose incorporation and with additive A1 remained lower than those of the standard resin, while thickness swelling remained higher. Within this strategy, the use of additive A2 stood out, indicating that component 2 plays a relevant role in promoting the formation of reactive intermediate species and improving the polymeric network structure. Nevertheless, resin performance was found to depend significantly on the synthesis conditions, particularly the additive concentration and the stage at which it was incorporated. In this regard, resin UF-7 exhibited the best overall performance, with the incorporation of 0,5 % additive after the first urea addition. This formulation achieved an internal bond value (0,40 N/mm²) close to that of the STD resin and lower thickness swelling (36,6 %), indicating improved dimensional stability. On the other hand, it exhibited a higher formaldehyde emission level (3,90 mg/m²h compared to 3,60 mg/m²h), which was associated with a higher formaldehyde-to-urea molar ratio. Thus, the results demonstrate that sucrose, particularly when combined with component 2 and incorporated through appropriate synthesis strategies, has the potential to replace melamine in adhesive resin formulations, contributing to the development of more sustainable adhesive systems.
The main objective of this work was to evaluate the potential of sucrose as a partial or total substitute for melamine in the formulation of melamine-urea-formaldehyde resins (mUF), used as adhesives in the production of wood particleboards. This approach arises from the recent classification of melamine as a substance of very high concern, encouraging the development of more sustainable and safer alternatives. Within the scope of this study, nine resins were produced: one through a strongly acidic process (UF-1) and seven through an alkaline–acid process (UF-2 to UF-8), as well as a standard (STD) resin, which was used as a reference to evaluate the performance of the others as adhesive systems for panel production, in accordance with the requirements of NP EN 312:2010. Two main sucrose incorporation strategies were investigated. The first consisted of incorporating sucrose into a strongly acidic synthesis process. This approach resulted in poorer mechanical performance, with an internal bond (IB) value of 0,22 N/mm² (compared to 0,39 N/mm² for the STD resin) and higher thickness swelling (51,3 % compared to 38,7 %). In contrast to the strongly acidic process, the second approach was based on the alkaline–acid process, in which either sucrose or an additive system (A1 and A2) was directly incorporated. These additives were formulated from sucrose combined with component 1 in the case of additive A1, and with components 1 and 2 in the case of additive A2. This approach led to improved performance compared to the strongly acidic process. However, the IB values obtained with direct sucrose incorporation and with additive A1 remained lower than those of the standard resin, while thickness swelling remained higher. Within this strategy, the use of additive A2 stood out, indicating that component 2 plays a relevant role in promoting the formation of reactive intermediate species and improving the polymeric network structure. Nevertheless, resin performance was found to depend significantly on the synthesis conditions, particularly the additive concentration and the stage at which it was incorporated. In this regard, resin UF-7 exhibited the best overall performance, with the incorporation of 0,5 % additive after the first urea addition. This formulation achieved an internal bond value (0,40 N/mm²) close to that of the STD resin and lower thickness swelling (36,6 %), indicating improved dimensional stability. On the other hand, it exhibited a higher formaldehyde emission level (3,90 mg/m²h compared to 3,60 mg/m²h), which was associated with a higher formaldehyde-to-urea molar ratio. Thus, the results demonstrate that sucrose, particularly when combined with component 2 and incorporated through appropriate synthesis strategies, has the potential to replace melamine in adhesive resin formulations, contributing to the development of more sustainable adhesive systems.
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Palavras-chave
Additives Swelling Internal Resistance 5-HMF Panels Aditivos Inchamento Resistência interna Painéis