Macromechanical and micromechanical properties of polymers with reduced density of entanglements

Abstract

The macromechanical and micromechanical properties of polypropylene, polylactide, and polystyrene with different entanglement densities and different crystallinities were tested. The mechanical properties were characterized by macroscale compression tests and microindentation hardness measurements. The entanglement density modified the mechanical properties only in the high‐deformation region, above the yield point, when the strain‐hardening occurred, and ca 10% lower stresses were measured for disentangled polymers. In the low‐deformation region, the influence of the entanglement density was negligible. The stiffness of semicrystalline polymers increased with their crystallinity and the stiffness of amorphous polymers increased with their glass transition temperature. For example, the elastic modulus was equal to 1.59 MPa for entangled polylactide, 1.68 MPa for partially disentangled polylactide, and 2.20 MPa for semicrystalline, disentangled polylactide. The stiffness‐related properties in both macroscale (compressive modulus, E, and yield stress, Y) and microscale (indentation modulus, EIT and indentation hardness, HIT) showed very similar trends, which was in perfect agreement with theoretical predictions and confirmed the reliability of our results. The supplementary, viscosity‐related properties from microindentation experiments (indentation creep, CIT, and elastic part of indentation work, ηIT) supported the above‐mentioned conclusions in the sense that also these two low‐deformation region properties were independent on the entanglement density.

Processability and physico‐mechanical properties of ultrahigh‐molecular‐weight polyethylene using low‐molecular‐weight olefin wax

“…The mechanical properties were affected by entanglement density, mainly in the higher deformation region rather than in the lower deformation region. [ 43 ]…”

European Database of Explanted UHMWPE Liners from Total Joint Replacements: Correlations among Polymer Modifications, Structure, Oxidation, Mechanical Properties and Lifetime In Vivo

“…The exact definitions of the above-listed micromechanical properties can be found in suitable reviews or textbooks dealing with micro- and/or nanoindentation [ 22 , 23 , 24 ]. A more detailed description of the MHI experiments, together with the illustration that the MHI measurements were reliable and reproducible, can be found also in our recent studies [ 25 , 26 , 27 ].…”

Biodegradable Thermoplastic Starch/Polycaprolactone Blends with Co-Continuous Morphology Suitable for Local Release of Antibiotics

“…Five micromechanical properties were obtained from F – h curves (where F is the loading force and h is the indenter penetration depth) according to ISO 14577-1 standard: indentation modulus ( E IT ), indentation hardness ( H IT ), Martens hardness ( H M ), indentation creep ( C IT ), and elastic part of indentation work ( η IT ). Figure 1 shows the principle of MHI measurement and evaluation in the case of our TPS/PCL blends; further details can be found in our recent papers [ 40 , 41 ].…”

“… Principle of MHI measurements, which were employed in this work: ( a ) Micromechanical properties were deduced from the experimental F – h curves (where F is the indenter loading force and h is the indenter penetration depth) by means of ( b ) formulas and ( c ) relations containing experimental parameters, such as maximum loading force ( F max ), slope at the beginning of the unloading curve ( S ), penetration depths at the beginning and end of the maximal load ( h 1 and h 2 ), and areas under loading and unloading curve ( W elast and W total ). Additional parameter, contact depth ( h c ), was calculated in terms of the Oliver and Pharr theory and employed in the calculation of E IT and H IT , as described in our previous work [ 41 , 42 ]. The figure shows real, representative F – h curves of TPS/PCL systems, which the illustrate substantial changes of all studied properties as a function of composition.…”