The Modulus of the Amorphous Phase of Semicrystalline Polymers

Abstract

A universal method for determining the modulus of the interlamellar amorphous phase of semicrystalline polymers was proposed. The basics of the method were presented on the example of high-density polyethylene (HDPE). The local deformation of the amorphous component was induced by the introduction of a swelling agent (hexane). The swelling-induced local strain and local stress of the interlamellar amorphous phase were estimated based on the changes of the long period and the yield stress, respectively. The determined modulus of the interlamellar amorphous phase of HDPE (≈40 MPa) was an order of magnitude higher than the modulus of the bulk rubbery amorphous phase of HDPE (≈3 MPa). The modulus of the interlamellar amorphous phase of other semicrystalline polymers, such as polypropylene (PP), low-density polyethylene (LDPE), and an ethylene−octane copolymer (EOC), was also determined and amounted to 50.3, 11.8, and 4.2 MPa, respectively. For polyethylene materials (HDPE, LDPE, and the EOC), a linear increase in the modulus of the interlamellar amorphous phase with increasing of the degree of crystallinity was observed. This effect was correlated with a decrease in "deformability" of the amorphous layers (a decrease in the swelling-induced local strain of amorphous layers for samples with higher crystallinity). The decrease in "deformability" of the amorphous component at low strains was probably caused by an increase in the density of stress transmitters (entanglements and tie molecules), which affected the mechanical properties (modulus) of the interlamellar regions. In the case of the material with the lowest degree of crystallinity (EOC, 26.2 vol%), the modulus of the interlamellar amorphous phase was similar to the modulus of the bulk rubbery amorphous phase, which indicated a very limited influence of the lamellar crystals on the stiffness of the amorphous regions.

A study on the synergetic effects of self/induced crystallization and nanoparticles on the mechanical properties of semi-crystalline polymer nanocomposites: experimental and analytical approaches

“…where, Em and Ea are the tensile modulus of semi-crystalline polymer and pure amorphous matrix, respectively, and k = ρm/ρcXc. Ea is reported to be 3 MPa in HDPE and accordingly, Ec was calculated to be 1.611 GPa [35].…”

Plastic Deformation of High Density Polyethylene with Extended-Chain Crystal Morphology

“…FEM model calculations performed for the oriented block copolymer structure [ 55 ] demonstrated that the first sinusoidal undulations were generated when the ratio of the elastic moduli exceeded 500 (at constant layer thickness). In semicrystalline polymers deformed above T g , this ratio is expected to be much higher (e.g., in polyethylene, PE, an overall modulus of elasticity of crystalline phase is about 50 GPa—elastic constants calculated for anisotropic PE crystal range from c 11 ≈ c 22 ≈ 10 GPa to c 33 ≈ 300 GPa [ 60 ], while that of amorphous layer is below 40 MPa [ 61 ], i.e., smaller by 3 order of magnitude), which can indicate their high susceptibility to microbuckling upon deformation.…”

A New Look at the Structure and Thermal Behavior of Polyvinylidene Fluoride–Camphor Mixtures

“…It also calls into question the applicability of the Gibbs–Thomson equation [ 74 ], which relates broad melting peaks of polymers to the thickness distribution of their crystalline lamellas. In the last few years, more and more evidence [ 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 ] contributing to the opinion that the distribution of lamellar thickness cannot fully explain the melting behavior of semicrystalline polymers appeared. For example, crystallites of the same size can melt at different temperatures depending on the thickness of adjacent amorphous regions [ 75 ].…”