| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 24.5 MB | Adobe PDF |
Authors
Abstract(s)
O PVC é um polímero bastante versátil utilizado em inúmeras aplicações,
designadamente no fabrico de tubagem plástica, durante o qual o PVC é submetido a
um processo de extrusão.
O grau de gelificação de compostos de PVC é um parâmetro que está diretamente
relacionado com a formulação e com as condições de processamento, sendo estes
fatores chave para estabelecer a qualidade de produto final.
Para determinar o grau de gelificação de um produto de PVC rígido é correntemente
usado o ensaio de resistência ao diclorometano, de acordo com a norma NP ISO
9852:2014 - Tubos termoplásticos – determinação das propriedades em tração, através
da qual se avalia a ocorrência de ataque do solvente ao PVC no caso de uma gelificação
deficiente. Contudo, a utilização de diclorometano acarreta problemas de nível
ambiental, de saúde e de segurança, devendo por isso reduzir-se a sua utilização o mais
possível.
O objetivo deste trabalho consistiu, por isso, em estudar métodos alternativos ao ensaio
de resistência ao diclorometano, nomeadamente avaliar a adequabilidade dos ensaios
de tração e de calorimetria diferencial de varrimento já preconizados nas novas versões
de normas, usando amostras extraídas de tubos de PVC rígido preparados para
tubagens de drenagem e de esgoto sem pressão.
Algumas das amostras caracterizadas foram ainda analisadas por microscopia
eletrónica de varrimento.
Os resultados obtidos com os diversos métodos alternativos foram comparados com os
resultados dos ensaios de resistência ao diclorometano.
Os resultados agora obtidos permitiram concluir que os métodos estudados não são
totalmente alternativos, mas sim complementares entre si, sendo que cada um
apresenta vantagens e desvantagens.
O ensaio de resistência ao diclorometano é o único que permite avaliar o grau de
gelificação em todo o perímetro do tubo, mas tem como principal desvantagem a sua
toxicidade. Apesar disso e porque também têm sido reportadas algumas desvantagens técnicas1, é aquele cujo resultado, nas normas de especificação de produto, continua a
ser considerado como decisor em caso de litígio.
As principais desvantagens dos métodos complementares são o método de preparação
das amostras para os ensaios de tração (que poderá influenciar os resultados obtidos),
e, no caso da calorimetria diferencial de varrimento, a necessidade de realizar um
número significativo de ensaios em amostras extraídas ao longo do perímetro do tubo,
pois embora permita quantificar o grau de gelificação, apenas permite a análise de
pequenas amostras de zonas específicas do tubo. Por fim, a microscopia eletrónica de
varrimento apenas permite visualizar zonas bem e mal gelificadas, não permitindo
extrair uma conclusão generalizada. 1: Por um lado, aponta-se o facto de ser necessário chanfrar as extremidades dos tubos a
imergir no diclorometano, processo este que pode provocar alguma degradação
termomecânica que facilite o ataque. Por outro, é referido que o ataque só ocorre quando o
PVC tem um grau de gelificação inferior a 50%, permitindo ainda assim aceitar amostras mal
gelificadas.
PVC is a very versatile polymer used in numerous applications, namely in the manufacture of plastic piping, during which the PVC is subjected to an extrusion manufacture process. The degree of gelation of PVC compounds is a parameter that is directly related to the formulation and the processing conditions, being these key factors to establish the final product quality. In order to determine the degree of gelation of a rigid PVC product, the dichloromethane resistance test according to NP ISO 9852: 2014 – Thermoplastics pipes – Determination of tensile properties is currently used to assess the occurrence of solvent attack on PVC in the case of a deficient gelation. However, the use of dichloromethane entails environmental, health and safety concerns and should therefore be reduced as far as possible. The main objective of this work was to study alternative methods to the dichloromethane resistance test, namely to evaluate the suitability of the traction and differential scanning calorimetry tests already recommended in the new standards versions, using samples extracted from rigid PVC pipes for drain and sewer pipes without pressure. Some of the characterized samples were further analyzed by scanning electron microscopy. The results obtained with the various alternative methods were compared with the results of the dichloromethane resistance tests. The obtained results allowed to conclude that the studied methods are not totally alternative, but complementary to each other, each one presenting advantages and disadvantages. The dichloromethane resistance test is the only one that allows assessing the degree of gelation around the perimeter of the pipe, but its main drawback is its toxicity. Despite this and because some technical disadvantages have also been reported2, it continues to be the one whose result, in the standards of product specification, is considered as being decisive in case of litigation. The main disadvantages of the complementary methods are the method of preparation of the samples for the tensile tests (which may influence the results obtained) and, in the case of differential scanning calorimetry, the need to perform a significant number of tests on samples drawn along the perimeter of the pipe, although it allows quantification of the degree of gelation, only allows the analysis of small samples of specific areas of the pipe. Finally, scanning electron microscopy only allows the visualization of well and poorly gelled zones, not allowing a general conclusion to be drawn. 2: On the one hand, it is pointed out that it is necessary to chamfer the ends of the tubes to be immersed in dichloromethane, a process that may cause some thermomechanical degradation that facilitates the attack. On the other hand, it is reported that the attack occurs only when the PVC has a degree of gelling of less than 50%, allowing still to accept badly gelified samples.
PVC is a very versatile polymer used in numerous applications, namely in the manufacture of plastic piping, during which the PVC is subjected to an extrusion manufacture process. The degree of gelation of PVC compounds is a parameter that is directly related to the formulation and the processing conditions, being these key factors to establish the final product quality. In order to determine the degree of gelation of a rigid PVC product, the dichloromethane resistance test according to NP ISO 9852: 2014 – Thermoplastics pipes – Determination of tensile properties is currently used to assess the occurrence of solvent attack on PVC in the case of a deficient gelation. However, the use of dichloromethane entails environmental, health and safety concerns and should therefore be reduced as far as possible. The main objective of this work was to study alternative methods to the dichloromethane resistance test, namely to evaluate the suitability of the traction and differential scanning calorimetry tests already recommended in the new standards versions, using samples extracted from rigid PVC pipes for drain and sewer pipes without pressure. Some of the characterized samples were further analyzed by scanning electron microscopy. The results obtained with the various alternative methods were compared with the results of the dichloromethane resistance tests. The obtained results allowed to conclude that the studied methods are not totally alternative, but complementary to each other, each one presenting advantages and disadvantages. The dichloromethane resistance test is the only one that allows assessing the degree of gelation around the perimeter of the pipe, but its main drawback is its toxicity. Despite this and because some technical disadvantages have also been reported2, it continues to be the one whose result, in the standards of product specification, is considered as being decisive in case of litigation. The main disadvantages of the complementary methods are the method of preparation of the samples for the tensile tests (which may influence the results obtained) and, in the case of differential scanning calorimetry, the need to perform a significant number of tests on samples drawn along the perimeter of the pipe, although it allows quantification of the degree of gelation, only allows the analysis of small samples of specific areas of the pipe. Finally, scanning electron microscopy only allows the visualization of well and poorly gelled zones, not allowing a general conclusion to be drawn. 2: On the one hand, it is pointed out that it is necessary to chamfer the ends of the tubes to be immersed in dichloromethane, a process that may cause some thermomechanical degradation that facilitates the attack. On the other hand, it is reported that the attack occurs only when the PVC has a degree of gelling of less than 50%, allowing still to accept badly gelified samples.
Description
Trabalho final de mestrado para obtenção do grau de mestre em Engenharia Química e Biológica
Keywords
Tubos de PVC PVC pipes Grau de gelificação Gelation grade Ensaios de resistência ao diclorometano Dichloromethane resistance tests Ensaio de tração Tensile tests Calorimetria diferencial de varrimento Differential scanning calorimetry Microscopia eletrónica de varrimento Scanning electron microscopy PVC
Citation
PIMENTA, Sara Isabel Soares - Avaliação do grau de gelificação do PVC : estudo de métodos alternativos ao ensaio de resistência ao diclorometano. Lisboa: Instituto Superior de Engenharia de Lisboa, 2017. Dissertação de mestrado.
Publisher
Instituto Superior de Engenharia de Lisboa