Publicação
Acetaldehyde generation in preforms with the use of recycled PET
| Resumo: | The production and recycling process for polyethylene terephthalate (PET) bottles for packaging soft drinks and mineral waters is still growing worldwide and improving constantly. Although, during the melting and processing of PET, especially recycled PET (rPET), degradation of the material occurs. The result of the degradation reactions is a severe drop in the molecular weight, which leads to the failing of intrinsic viscosity, melt strength and melt processability and finally, to poor usage properties and a low quality of the bottles obtained. One of the most common degradation products is acetaldehyde (AA). Due to its low boiling point, 21°C, AA is able to diffuse out of PET into the beverage content of the PET bottle. The diffusion of AA into packaged contents is of concern due to its limited threshold for the taste and odour that can be detected by consumers. The purpose of this study is to examine the AA generation, the failing of the intrinsic viscosity and the colour degradation from reprocessed rPET when exposed to different drying and injection conditions. An initial model was developed to analyse the interaction, magnitude and influence of each processing condition in a twin-tower desiccant dryer and a mono-cavity PET preform injection moulding system. It was found an optimal condition capable of reducing AA concentration in the preform, without compromising a significant failing of the intrinsic viscosity, with minimal impact in colour degradation. The modification of an existing drying and injection moulding program was applied under the optimal result given by the model and additional studies regarding moisture content and intrinsic viscosity were conducted. AA was reduced by 61% after drying, while the drop in the intrinsic viscosity was significantly reduced by heat preservation of the settled drying temperature. There was no significant impact in colour observed. An agreement between the modelling results and observed trends from mono-cavity injection moulding was achieved. The groundwork was placed and made further improvements in the industrial production of preforms containing 100% content of recycled PET. |
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| Autores principais: | Fernandes, Ana Luísa Geraldo |
| Assunto: | PET Recycling Acetaldehyde Intrinsic viscosity Drying Injection moulding Reciclagem Acetaldeído Viscosidade intrínseca Secagem Moldação por injeção |
| Ano: | 2020 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | The production and recycling process for polyethylene terephthalate (PET) bottles for packaging soft drinks and mineral waters is still growing worldwide and improving constantly. Although, during the melting and processing of PET, especially recycled PET (rPET), degradation of the material occurs. The result of the degradation reactions is a severe drop in the molecular weight, which leads to the failing of intrinsic viscosity, melt strength and melt processability and finally, to poor usage properties and a low quality of the bottles obtained. One of the most common degradation products is acetaldehyde (AA). Due to its low boiling point, 21°C, AA is able to diffuse out of PET into the beverage content of the PET bottle. The diffusion of AA into packaged contents is of concern due to its limited threshold for the taste and odour that can be detected by consumers. The purpose of this study is to examine the AA generation, the failing of the intrinsic viscosity and the colour degradation from reprocessed rPET when exposed to different drying and injection conditions. An initial model was developed to analyse the interaction, magnitude and influence of each processing condition in a twin-tower desiccant dryer and a mono-cavity PET preform injection moulding system. It was found an optimal condition capable of reducing AA concentration in the preform, without compromising a significant failing of the intrinsic viscosity, with minimal impact in colour degradation. The modification of an existing drying and injection moulding program was applied under the optimal result given by the model and additional studies regarding moisture content and intrinsic viscosity were conducted. AA was reduced by 61% after drying, while the drop in the intrinsic viscosity was significantly reduced by heat preservation of the settled drying temperature. There was no significant impact in colour observed. An agreement between the modelling results and observed trends from mono-cavity injection moulding was achieved. The groundwork was placed and made further improvements in the industrial production of preforms containing 100% content of recycled PET. |
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