Miscible/partially‐miscible blends of polypropylene—the mechanisms responsible for the decrease of yield stress

Abstract

In miscible or partially-miscible blends of semicrystalline polymer/non-cocrystallizing low molecular weight component, a decrease of the value of yield stress in comparison to reference (pure) polymer is usually observed. On the example of model polypropylene/nonadecane systems, the mechanisms responsible for the decrease of the yield stress have been identified. It has been proved that during the deformation of polypropylene/nonadecane blends containing low amount of nonadecane (up to 5 wt %) the reduction of the yield stress is caused only by the swelling of interlamellar regions. In the case of the systems containing a moderate amount of nonadecane (7-10 wt %), the reduction of the yield stress is caused by the swelling of interlamellar regions and the reduction of the sample cross-section effectively participating in transferring of tensile stress. In blends containing nonadecane in the amount of 15-30 wt % the reduction of the yield stress is caused by the swelling of interlamellar regions and strong asymmetrization of nonadecane microdomains, resulting in localizing the deformation along interspherulitic regions and a drastic reduction of the content of polypropylene matrix, effectively participating in transferring of tensile stress between adjacent spherulites.

The Modulus of the Amorphous Phase of Semicrystalline Polymers

“…Moreover, the calorimetric (degree of crystallinity and melting temperature) and mechanical (Young modulus and yield stress) measurements for the reference sample and the hexane-swollen system after desorption of hexane indicated no dissolution of the crystals during the process of hexane sorption. The observed change of the mechanical properties of the swollen polyethylene (decrease in the yield stress) was explained by us in the previous papers ,, and will be used to estimate the value of the local stress of the amorphous component in the present work (see Section ). The decrease in the Young modulus for the swollen system and the influence of this phenomenon on the determined value of the modulus of the amorphous phase will be discussed later in this paper.…”

Plasticization of Polylactide after Solidification: An Effectiveness and Utilization for Correct Interpretation of Thermal Properties

“…As stated in the papers [33][34][35][36], the decrease in yield strength observed for a particular polymer is primarily associated with a reduction in the thickness of crystals or the degree of crystallinity of these samples. In our recent works [23,37] we analyzed the effect of introducing molecules of wax or nanodecane into the amorphous phase regions of polypropylene. We revealed that low molecular weight compounds do not lead to reduction of the thickness of polypropylene crystals and degree of The analysis of the tensile stress-strain curves and the data in Table 2 shows that there is a large difference between the plasticized and neat polylactide samples.…”

“…The shift of T m toward lower values of temperature is attributed to the plasticizing effect of the modifier, that is TEC. Our previous works [23,37] revealed that the change of the melting temperature of polypropylene/modifier systems may be caused by the decrease of equilibrated melting temperature of polymer crystal, T m , of an infinite stack of extended chain crystals, large in directions perpendicular to the chain axis and where the chain ends have established an equilibrium state of pairing. Additionally, we correlated this phenomenon with the changes (decrease) in the value of yield stress.…”

Role of free volume in mechanical behaviors of side chain lcp grafted products of high density polyethylene

“…The graft copolymerization of BPOCPMA onto HDPE was also performed via bulk polymerization method. The reaction mixtures with varying compositions were prepared by mixing HDPE powder, BPOCPMA (5,10,15,20,30, 40% of the mixture) and DCP initiator (2% with respect to weight of BPOCPMA) in a mortar with extensive hand grinding. The mixtures were then heated up to 140 °C in vacuum and kept at this temperature for an hour.…”

“…Mechanical performance of semicrystalline polymers under load is dependent on plastic deformation mechanism [9] as well as on the chemical structure, configuration, conformation and on microstructure [10][11][12][13][14]. The plastic deformation is a complicated process and involves changes in both amorphous and crystalline phases, however, the involvement varies with the stress applied [15][16][17]. In amorphous phase the macromolecules are relatively mobile at temperatures above the glass transition, and the phase has relatively low resistance to the deformation [18].…”