Performance prediction of weldline structure in amorphous polymers

Abstract

The presence of a weldline generally reduces the mechanical strength of injection molded parts. A typical remedy to eliminate the problem of weak weldline structure has been to increase the melt temperature. This, however, is not an acceptable solution in some situations. A general solution to the weak weldline problem requires an in-depth understanding of the thermomechanical history of the injection molding process. A theoretical model for the strength of weldlines is presented that provides a comprehensive physical insight of the bonding process at the weldline interface. The model is based on the self-diffusion of molecular chains across the polymer-polymer interface and the frozen-in orientation that remains parallel to the interface. Both factors are analyzed separately and then superimposed to predict the strength of weldlines from known processing conditions and geometry. Experimental results show good correlation with predictions.

Weld line behaviour of exfoliated and toughened polypropylene layered silica nanocomposites

“…The poor weld line strength of micron-sized fiber-filled polymers have been reported to be due to perpendicular alignment of the filler at weld line plane and to their non-uniform distribution [21]. In the weld line region, the nanoparticles may also hinder molecular diffusion across the weld line interphase and /or promote planar molecular orientation parallel to weld line plane and hence lead to incomplete molecular entanglement [16]. The resultant weld line morphology in Figure 2 clearly presents the significantly large weld line region resulting from low degree of molecular diffusion.…”

“…Weld line is undesirable when the strength, long term durability and surface quality is a concern. The losses in abovementioned performances with presence of weld line for composites usually much more pronounced than that for their counterparts owing to much more complicated morphology in the weld line region, There is no doubt that it might be possible to overcome these drawbacks through development of a special weld line morphology via molding temperature, injection velocity, holding pressure at various degrees depending on materials [16][17].…”

Determinação da redução da resistência à tração em corpos de prova com Weld Line

“…A solução da Equação 3 permite determinar a área da trinca (A Trinca ) [4], considerando a seção transversal do corpo de provas um retângulo perfeito e que a trinca como sendo igual em todo o perímetro, então, a solução das Equações 3 e 4 permitiu determinar o tamanho da trinca, "a", para cada temperatura de injeção. Para a determinação da tensão máxima o para o corpo de prova sem weld line foi adotada a temperatura média de processamento do PS de 230 O C. Sabe-se que a tensão pode ter um pouco de variação dentro da faixa recomendada de processamento.…”

“…A análise do ângulo de junção dos fluxos pode determinar se irá existir uma linha de junção ou solda [2,3]. Vários pesquisadores têm empreendido esforços em estudos que abordam a redução da resistência devido à existência de linhas de soda e linhas de junção [4,5,6,7,8,9]. Na linha solda existe a difusão molecular entre as duas superfícies, pois quanto maior for a temperatura e o tempo de permanência na temperatura acima da T g maior será a difusão na interface [10,11,12].…”

Untersuchung zur Vorhersage der Bindenahtfestigkeit in spritzgegossenen Formteilen

“…-Molekülorientierung und Verschlaufungsdichte haben Einfluß auf die Bindenahtfestigkeit, was zumindest durch physikalische Modellrechnungen aufgezeigt wurde 7) . -Die Kristallinität an Bindenähten hat Besonderheiten, die zwar dargestellt werden 8) , zu deren Einfluß auf die Nahtfestigkeit es hingegen bisher keine Veröffentli-chungen zu geben scheint.…”