Strong synergistic improvement of mechanical properties in HDPE/COC blends with fibrillar morphology

Abstract

High‐density polyethylene/cycloolefin copolymer (HDPE/COC) blends with fibrous morphology were prepared. Mechanical properties in the whole concentration range were measured in both macroscale (tensile measurements) and microscale (microindentation hardness testing). Strong improvement of mechanical performance was observed namely for the blends with soft HDPE matrix reinforced with the stiff oriented COC fibers. The combined results from scanning electron microscopy, mechanical properties measurements and theoretical calculations based on predictive models showed that the interfacial adhesion was unusually high, which could be attributed to the excellent compatibility or even partial miscibility of the blend components. The HDPE/COC blends with 10–40% of COC showed the synergistic improvement of the tensile energy to break (ETB) that exceeded the ETB of both individual components. Also the stiffness of the blends, represented by the elastic modulus, the yield strength and the microhardness were very high, above the theoretical values predicted by the equivalent box model. POLYM. ENG. SCI., 58:1955–1964, 2018. © 2017 Society of Plastics Engineers

Structure Characterization and Biodegradation Rate of Poly(ε-caprolactone)/Starch Blends

“…Figures 1A,E show a typical pure component morphology of the blend, i.e., PCL and wheat thermoplastic starch, respectively. Due to the plasticization procedure used, the TPS structure was almost homogeneous, in agreement with our previous work (Ostafinska et al, 2018). The other three micrographs, Figures 1B-D, demonstrate appropriate heterogeneous structure of the PCL/TPS blends.…”

“…Moreover, for H IT , the calculation was made for both minimal interfacial adhesion (A = 0; short dashed line) and maximal interfacial adhesion (A = 1; long dashed line). The fact that the experimental values of E IT were higher than the EBM predictions ( Figure 5A) indicated good compatibility and strong interface between PCL and TPS (Kolařík, 2000;Vacková et al, 2012;Ostafinska et al, 2018). The good PCL/TPS compatibility was confirmed also by the experimental values of H IT ( Figure 5B) which corresponded better to the EBM prediction based on maximal interfacial adhesion ( Figure 5B, short dashed line corresponding to Equation 4 with A = 1) than to the EBM prediction based on minimal interfacial adhesion ( Figure 5B, long dashed line corresponding to Equation 4 with A = 0).…”

“…%) and distilled water (water/starch = 6/1) were premixed with a magnetic stirrer for 30 min at laboratory temperature and then the mixture was kept in conditions of continuous agitation for another 15 min at elevated temperature (above 65 • C) until the viscosity increased significantly. Then the mixture was cast in a Petri dish into a form of about 2-mm-thick film and dried at laboratory temperature (at relative humidity RH = 50-55%) for 2-3 days, followed by 4 days in a desiccator with saturated solution of sodium bromide (RH = 57%) (Ostafinska et al, 2018). In the following step, the thermoplastic starch film was cut into small pieces and after that homogenized by meltmixing at screw speed of 160 rpm and temperature of 130 • C for 8 min.…”

“…The additivity law holds very well for polymer composites with infinitely long oriented fibers or for semicrystalline polymers (containing amorphous and crystalline phases). For most other polymer systems, however, the additivity law represents the upper achievable limit unless synergistic effects are observed (Ostafińska et al, 2017a;Ostafinska et al, 2018). In most cases, real mechanical properties are below the additivity law predictions due to the interface, which usually represents the weakest point.…”

“…In order to understand v cr parameter properly, it is also important to realize that it represents the composition at which a small fraction of minority phase may start to be continuous according to percolation theory, while most of this phase still exhibits particulate structure. This is more evident if we calculate all volume fractions v ij (i.e., v 1p , v 2p , v 1s , and v 2s in Equations 3 and 4) as described elsewhere (Kolařík, 1996;Ostafinska et al, 2018). Therefore, default value of critical volume fraction may be regarded as a parameter, which (i) represents the theoretically predicted composition at which the first signs of co-continuity may appear and which (ii) corresponds reasonably well with experimental results if more detailed analysis of morphology for given system is not available (Kolařík, 1995(Kolařík, , 1996(Kolařík, , 2000.…”