بررسي تاثير نوع پليمر هسته-پوسته بر ريز ساختار ذرات بهبوددهنده ضربه آكريليكي و عملكرد آنها در افزايش مقاومت ضربه در آميزه PVC

Investigation of the Effect of Core–Shell Polymer Type on the Microstructure of Acrylic Impact Modifiers an‎d Their Performance in Enhancing Impact Strength of PVC Compounds

مهندسي شيمي

In recent years, the use of acrylic core–shell structures as impact modifiers, foam property regulators, an‎d processing aids has gained considerable attention. The type of core an‎d shell polymers has a significant effect on the properties an‎d performance of these materials in enhancing impact resistance in PVC compounds, which is investigated in this study. For this purpose, polymeric latexes containing nanoparticles with a rubbery core an‎d a hard, glassy shell were synthesized via semi-continuous emulsion polymerization. Butyl acrylate an‎d ethylhexyl acrylate were used separately an‎d simultaneously as core monomers, while methyl methacrylate an‎d styrene were used both individually an‎d in combination as shell monomers. The chemical structures of the poly(butyl acrylate) an‎d poly(butyl acrylate–ethylhexyl acrylate) copolymer cores, as well as the poly(methyl methacrylate), polystyrene, an‎d their copolymer shells, were characterized using Fourier-transform infrared spectroscopy (FTIR). The average size an‎d distribution of the core–shell particles were analyzed using dynamic light scattering (DLS). The mean particle size ranged from 20 to 50 nm, an‎d observations showed that the diameter of the copolymer poly(butyl acrylate–ethylhexyl acrylate) core particles was 5 nm larger than that of the poly(butyl acrylate) homopolymer core. The particle size distribution index (PDI) was significantly lower than 1, indicating a narrow size distribution. Furthermore, transmission electron microscopy (TEM) results confirmed that the core–shell nanostructures were successfully synthesized via semi-continuous emulsion polymerization. Based on the TEM images, the ratio of core diameter to shell thickness was directly correlated with the ratio of the starting materials. For a poly(butyl acrylate) core diameter of 20.56 nm, the shell thickness was 9.76 nm for MMA an‎d 13.3 nm for PS. The Fox equation was used to estimate the glass transition temperature (Tg) of the copolymers in both the core an‎d the shell. Analysis showed that the soft PBA-co-EHA core, with Tg ≈ −57 °C, provides high flexibility an‎d desirable impact energy absorption, while the hard PMMA–PS shell, with Tg ≈ 100–105 °C, ensures the mechanical stability of the system. The considerable Tg difference between the core an‎d shell enables controlled stress transfer an‎d improved toughness in the PVC matrix. To eva‎luate impact resistance, the synthesized core–shell particles were incorporated into PVC compounds along with other conventional additives, an‎d the impact strength of each compound was measured using the Charpy test. The results showed that the addition of 3 phr of the core–shell particles increased the impact resistance of PVC. In particular, the BE/MS sample raised the impact strength of neat PVC from approximately 2.5 kJ to about 15.5 kJ, which is very close to the reported value for the commercial sample DL-698.

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