The role of dry and wet isothermal annealing treatment on the structure and the mechanical properties of isotactic polypropylene fibers

Abstract

Dry and wet annealing of isotactic polypropylene fibers was carried out under constant length at 120°C in air and in glycerine environments with annealing times ranging from 1 to 30 h. A detailed analysis of the infrared spectrum of samples annealed, especially in air, showed clear evidence of the surface oxidation as indicated by the appearance of oxygen containing functional groups. Annealing was found to lead to an improved structural organization as indicated by the crystallinity, crystallite size, and orientation measurements using X‐ray diffraction and infrared spectroscopy methods. Analysis of the X‐ray diffraction measurements showed a gradual transformation of metastable smectic phase to a more stable α‐monoclinic phase with increasing annealing time. Crystallinity, crystallite size, and orientation measurements performed for the samples annealed in air and in glycerine environments showed no distinct difference. Mechanical properties of the annealed samples were influenced by the annealing environment. Annealing in an air environment resulted in a continuous loss of tensile strength up to the annealing time of 12 h due to an oxidation related chain scission mechanism. On the other hand, annealing in glycerine environment resulted in a continuous and gradual increase of tensile strength without loss of physical form up to the annealing time of 30 h. It is suggested that wet annealing in glycerine environment should be used to obtain improved tensile strength values. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Effect of processing parameters of the continuous wet spinning system on the crystal phase of PVDF fibers

“…Furthermore, the voids were reduced by heat setting and mostly removed by the subsequent rolling process. As a result, the fiber showed improved dimensional stability, no structural defects, and enhanced mechanical properties …”

“…As a result, the fiber showed improved dimensional stability, no structural defects, and enhanced mechanical properties. [23][24][25] Figure 9 shows the piezoelectric constants of the heat-set and the hot-rolled PVDF fibers with and without poling. Basically, no significant piezoelectric response could be obtained from the fibers without applying the poling process, regardless of postprocessing.…”

Melt spinning of high-strength fiber from low-molecular-weight polypropylene

“…It is known that the oriented semicrystalline fibers are rarely in their equilibrium state leading to the dimensional instability and shrinkage caused by temperature, moisture, and load. Heat setting with tension at an elevated temperature but below the melting temperature for a specific amount of time, can reduce the residual stresses that persist from the melt‐spinning stage . Therefore, heat setting under appropriate conditions can stabilize the fibers against shrinkage, dimensional changes, and reduce of structural defects .…”

Effect of crystalline structure on the mechanical response of polypropylene under cyclic deformation

“…Changes in the crystalline structure of PP driven by annealing are accompanied by the evolution of molecular architecture in the amorphous phase [16] : (i) growth of chain mobility in the bulk amorphous phase, due to its loosening caused by decay in the number of chains in the amorphous state and the initiation of microvoids [14] ; and (ii) reduction of the mobility of segments in the rigid amorphous phase, driven by smectic-monoclinic transition [20] and microstructural rearrangement (interlamellar thickening) [16] .…”

“…4. Formation of short lamellar structures due to the melting/recrystallization of crystallites, accompanied by thermo-oxidative degradation (scission of chains in the amorphous matrix) at a very high T a , in the close vicinity of the melting temperature [20] .…”