Relating microhardness to morphology in styrene/butadiene block copolymer/polystyrene blends

Mechano-Chemical Properties of Electron Beam Irradiated Polyetheretherketone

In this study, the mechano-chemical properties of aromatic polymer polyetheretherketone (PEEK) samples, irradiated by high energy electrons at 200 and 400 kGy doses, were investigated by Nanoindentation, Brillouin light scattering spectroscopy and Fourier-transform infrared spectroscopy (FTIR). Irradiating electrons penetrated down to a 5 mm depth inside the polymer, as shown numerically by the monte CArlo SImulation of electroN trajectory in sOlids (CASINO) method. The irradiation of PEEK samples at 200 kGy caused the enhancement of surface roughness by almost threefold. However, an increase in the irradiation dose to 400 kGy led to a decrease in the surface roughness of the sample. Most likely, this was due to the processes of erosion and melting of the sample surface induced by high dosage irradiation. It was found that electron irradiation led to a decrease of the elastic constant C₁₁, as well as a slight decrease in the sample’s hardness, while the Young’s elastic modulus decrease was more noticeable. An intrinsic bulk property of PEEK is less radiation resistance than at its surface. The proportionality constant of Young’s modulus to indentation hardness for the pristine and irradiated samples were 0.039 and 0.038, respectively. In addition, a quasi-linear relationship between hardness and Young’s modulus was observed. The degradation of the polymer’s mechanical properties was attributed to electron irradiation-induced processes involving scission of macromolecular chains.

Macro-, Micro- and Nanomechanical Characterization of Crosslinked Polymers with Very Broad Range of Mechanical Properties

This work is focused on the comparison of macro-, micro- and nanomechanical properties of a series of eleven highly homogeneous and chemically very similar polymer networks, consisting of diglycidyl ether of bisphenol A cured with diamine terminated polypropylene oxide. The main objective was to correlate the mechanical properties at multiple length scales, while using very well-defined polymeric materials. By means of synthesis parameters, the glass transition temperature (T_g) of the polymer networks was deliberately varied in a broad range and, as a result, the samples changed their mechanical behavior from very hard and stiff (elastic moduli 4 GPa), through semi-hard and ductile, to very soft and elastic (elastic moduli 0.006 GPa). The mechanical properties were characterized in macroscale (dynamic mechanical analysis; DMA), microscale (quasi-static microindentation hardness testing; MHI) and nanoscale (quasi-static and dynamic nanoindentation hardness testing; NHI). The stiffness-related properties (i.e., storage moduli, indentation moduli and indentation hardness at all length scales) showed strong and statistically significant mutual correlations (all Pearson′s correlation coefficients r > 0.9 and corresponding p-values < 0.001). Moreover, the relations among the stiffness-related properties were approximately linear, in agreement with the theoretical prediction. The viscosity-related properties (i.e., loss moduli, damping factors, indentation creep and elastic work of indentation at all length scales) reflected the stiff-ductile-elastic transitions. The fact that the macro-, micro- and nanomechanical properties exhibited the same trends and similar values indicated that not only dynamic, but also quasi-static indentation can be employed as an alternative to well-established DMA characterization of polymer networks.

From Disposal to Technological Potential: Reuse of Polypropylene Waste from Industrial Containers as a Polystyrene Impact Modifier

The practice of recycling over the years has been increasingly encouraged, with the aim being the manufacturing of materials that contribute to sustainable development. In light of this, the present work evaluated the potential of mixtures of polystyrene (PS)/recycled copolymer polypropylene (PPr), using styrene-(ethylene/butylene)-styrene (SEBS) as a compatibilizing agent. Initially, the mixtures were prepared in a co-rotational twin-screw extruder, and, afterwards, the extruded granules were molded by injection. The properties of torque rheometry, impact strength, tensile properties, differential scanning calorimetry (DSC), heat deflection temperature (HDT), and scanning electron microscopy (SEM) were evaluated. The formulation PS/PPr/SEBS (70/20/10 %wt.) demonstrated an increase in viscosity, corroborating with an increase of 123% and 227% in the elongation at break and impact strength, respectively, compared to neat PS. Though the elastic modulus and tensile strength suffered losses, the reduction was not drastic. Furthermore, the addition of a semi-crystalline recycled material in the amorphous matrix (PS) contributed to an increase in thermomechanical strength, as seen in the HDT. The morphology revealed that SEBS is effective in making PS/PPr mixtures compatible because the dispersed phase is well adhered to the PS matrix and promotes greater morphological stability. Thus, it is possible to add value to discarded material and reduce the costs of the final product, which can reduce pollution.

Nanofiller Dispersion, Morphology, Mechanical Behavior, and Electrical Properties of Nanostructured Styrene-Butadiene-Based Triblock Copolymer/CNT Composites

A nanostructured linear triblock copolymer based on styrene and butadiene with lamellar morphology is filled with multiwalled carbon nanotubes (MWCNTs) of up to 1 wt% by melt compounding. This study deals with the dispersability of the MWCNTs within the nanostructured matrix and its consequent impact on block copolymer (BCP) morphology, deformation behavior, and the electrical conductivity of composites. By adjusting the processing parameters during melt mixing, the dispersion of the MWCNTs within the BCP matrix are optimized. In this study, the morphology and glass transition temperatures (Tg) of the hard and soft phase are not significantly influenced by the incorporation of MWCNTs. However, processing-induced orientation effects of the BCP structure are reduced by the addition of MWCNT accompanied by a decrease in lamella size. The stress-strain behavior of the triblock copolymer/MWCNT composites indicate higher Young's modulus and pronounced yield point while retaining high ductility (strain at break ~ 400%). At a MWCNT content of 1 wt%, the nanocomposites are electrically conductive, exhibiting a volume resistivity below 3 × 103 Ω·cm. Accordingly, the study offers approaches for the development of mechanically flexible functional materials while maintaining a remarkable structural property profile.

Micromechanical Characterization of Complex Polypropylene Morphologies by HarmoniX AFM

This paper examines the capability of the HarmoniX Atomic Force Microscopy (AFM) technique to draw accurate and reliable micromechanical characterization of complex polymer morphologies generally found in conventional thermoplastic polymers. To that purpose, injection molded polypropylene samples, containing representative morphologies, have been characterized by HarmoniX AFM. Mapping and distributions of mechanical properties of the samples surface are determined and analyzed. Effects of sample preparation and test conditions are also analyzed. Finally, the AFM determination of surface elastic moduli has been compared with that obtained by indentation tests, finding good agreement among the results.

Thermal Conductive and Mechanical Properties of Polymeric Composites Based on Solution-Exfoliated Boron Nitride and Graphene Nanosheets: A Morphology-Promoted Synergistic Effect

In this work, we reported a synergistic effect of boron nitride (BN) with graphene nanosheets on the enhancement of thermal conductive and mechanical properties of polymeric composites. Here, few layered BN (s-BN) and graphene (s-GH) were used and obtained by liquid exfoliation method. The polystyrene (PS) and polyamide 6 (PA) composites were obtained via solution blending method and subsequently hot-pressing. The experimental results suggested that the thermal conductivity (TC) of the PS and PA composites increases with additional introduction of s-BN. For example, compared with the composites containing 20 wt % s-GH, additional introduction of only 1.5 wt % s-BN could increase the TC up to 38 and 34% in polystyrene (PS) and polyamide 6 (PA) matrix, respectively. Meanwhile, the mechanical properties of the composites were synchronously enhanced. It was found that s-BN filled in the interspaces of s-GH sheets and formed s-BN/s-GH stacked structure, which were helpful for the synchronously improving TC and mechanical properties of the polymeric materials.

Effect of compatibilizing agents on the physical properties of iPP/HDPE organoclay blends

Blends of isotactic polypropylene (iPP) and high density polyethylene (HDPE), with and without compatibilizers and with different organoclay amounts (1%, 3%, and 5%), were systematically investigated to assess the effect of the additives on the crystallinity of the blends, as well as the correlation between the microhardness, H and the Young’s modulus E. The compatibilizers used were: maleic anhydride grafted styrene ethylene butadiene styrene (SEBS-g-MAH), maleic anhydride grafted polyethylene (PE-g-MAH), maleic anhydride grafted polypropylene (PP-g-MAH), ethylene propylene diene monomer (EPDM), and maleic anhydride grafted EPDM (EPDM-g-MAH). The thermal properties and crystallization behavior were determined by differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). Macro- and micromechanical properties were also investigated. The results obtained showed that the addition of clay slightly increases the crystallinity αWAXS of the blends. However, the hardness H decreases enormously only by adding 1 wt% of clay. With higher clay amounts, H increases again. The relationship between the Young’s modulus E and the hardness H for all the studied blends was found to be somewhat higher than the one obtained for polyethylene (PE) samples with different morphologies.

Estudo comparativo de diferentes tipos de polibutadieno na tenacificação de poliestireno

Neste trabalho foi avaliada a tenacificação de poliestireno (PS) utilizando três tipos de polibutadieno (PB): polibutadieno baixo-cis (PBb), polibutadieno alto-cis (PBa) e copolímero em bloco (SBS) de estireno e butadieno (PBco). Foi observado um aumento na resistência ao impacto de 138, 208 e 823%, quando foram utilizados polibutadieno baixo-cis, polibutadieno alto-cis e copolímero em bloco de estireno e butadieno respectivamente. Os materiais apresentaram morfologia dispersa com domínios de polibutadieno distribuídos aleatoriamente na matriz de poliestireno, cujo tamanho foi inferior a 1 µm. A energia de ativação para o escoamento foi calculada segundo a equação de Arrhenius e variou de 34 a 71 kJ/mol. Em todos os experimentos reológicos as misturas poliméricas apresentaram comportamento pseudoplástico.