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Post-Processing Time Dependence of Shrinkage and Mechanical Properties of Injection-Molded Polypropylene

Dimensions of the injection-molded semi-crystalline materials (polymeric products) decrease with the time that elapses from their formation. The post-molding shrinkage is an effect of secondary crystallization; the increase in the degree of polymer crystallinity leads to an increase in stiffness and...

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Autores principales: Kościuszko, Artur, Marciniak, Dawid, Sykutera, Dariusz
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7793073/
https://www.ncbi.nlm.nih.gov/pubmed/33374589
http://dx.doi.org/10.3390/ma14010022
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author Kościuszko, Artur
Marciniak, Dawid
Sykutera, Dariusz
author_facet Kościuszko, Artur
Marciniak, Dawid
Sykutera, Dariusz
author_sort Kościuszko, Artur
collection PubMed
description Dimensions of the injection-molded semi-crystalline materials (polymeric products) decrease with the time that elapses from their formation. The post-molding shrinkage is an effect of secondary crystallization; the increase in the degree of polymer crystallinity leads to an increase in stiffness and decrease in impact strength of the polymer material. The aim of this study was to assess the changes in the values of post-molding shrinkage of polypropylene produced by injection molding at two different temperatures of the mold (20 °C and 80 °C), and conditioned for 504 h at 23 °C. Subsequently, the samples were annealed for 24 h at 140 °C in order to conduct their accelerated aging. The results of shrinkage tests were related to the changes of mechanical properties that accompany the secondary crystallization. The degree of crystallinity of the conditioned samples was determined by means of density measurements and differential scanning calorimetry. It was found that the changes in the length of the moldings that took place after removal from the injection mold were accompanied by an increase of 20% in the modulus of elasticity, regardless of the conditions under which the samples were made. The differences in the shrinkage and mechanical properties of the samples resulting from mold temperature, as determined by tensile test, were removed by annealing. However, the samples made at two different injection mold temperature values still significantly differed in impact strength, the values of which were clearly higher for the annealed samples compared to the results determined for the samples immediately after the injection molding.
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spelling pubmed-77930732021-01-09 Post-Processing Time Dependence of Shrinkage and Mechanical Properties of Injection-Molded Polypropylene Kościuszko, Artur Marciniak, Dawid Sykutera, Dariusz Materials (Basel) Article Dimensions of the injection-molded semi-crystalline materials (polymeric products) decrease with the time that elapses from their formation. The post-molding shrinkage is an effect of secondary crystallization; the increase in the degree of polymer crystallinity leads to an increase in stiffness and decrease in impact strength of the polymer material. The aim of this study was to assess the changes in the values of post-molding shrinkage of polypropylene produced by injection molding at two different temperatures of the mold (20 °C and 80 °C), and conditioned for 504 h at 23 °C. Subsequently, the samples were annealed for 24 h at 140 °C in order to conduct their accelerated aging. The results of shrinkage tests were related to the changes of mechanical properties that accompany the secondary crystallization. The degree of crystallinity of the conditioned samples was determined by means of density measurements and differential scanning calorimetry. It was found that the changes in the length of the moldings that took place after removal from the injection mold were accompanied by an increase of 20% in the modulus of elasticity, regardless of the conditions under which the samples were made. The differences in the shrinkage and mechanical properties of the samples resulting from mold temperature, as determined by tensile test, were removed by annealing. However, the samples made at two different injection mold temperature values still significantly differed in impact strength, the values of which were clearly higher for the annealed samples compared to the results determined for the samples immediately after the injection molding. MDPI 2020-12-23 /pmc/articles/PMC7793073/ /pubmed/33374589 http://dx.doi.org/10.3390/ma14010022 Text en © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Kościuszko, Artur
Marciniak, Dawid
Sykutera, Dariusz
Post-Processing Time Dependence of Shrinkage and Mechanical Properties of Injection-Molded Polypropylene
title Post-Processing Time Dependence of Shrinkage and Mechanical Properties of Injection-Molded Polypropylene
title_full Post-Processing Time Dependence of Shrinkage and Mechanical Properties of Injection-Molded Polypropylene
title_fullStr Post-Processing Time Dependence of Shrinkage and Mechanical Properties of Injection-Molded Polypropylene
title_full_unstemmed Post-Processing Time Dependence of Shrinkage and Mechanical Properties of Injection-Molded Polypropylene
title_short Post-Processing Time Dependence of Shrinkage and Mechanical Properties of Injection-Molded Polypropylene
title_sort post-processing time dependence of shrinkage and mechanical properties of injection-molded polypropylene
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7793073/
https://www.ncbi.nlm.nih.gov/pubmed/33374589
http://dx.doi.org/10.3390/ma14010022
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