Mechanical properties draw ratio effects

Figures 20.13 and 20.14 describe the effect of dibutyltin dilaurate (DBTDL) on the tensile strength and tensile modulus for the 25/75 LCP/PEN blend fibers at draw ratios of 10 and 20 [13]. As expected, the addition of DBTDL slightly enhances the mechanical properties of the blends up to ca. 500 ppm of DBTDL. The optimum quantity of DBTDL seems to be about 500 ppm at a draw ratio of 20. However, the mechanical properties deteriorate when the concentration of catalyst exceeds this optimum level. From the previous relationships between the rheological properties and the mechanical properties, it can be discerned that the interfacial adhesion and the compatibility between the two phases, PEN and LCP, were enhanced. Hence, DBTDL can be used as a catalyst to achieve reactive compatibility in this blend system. This suggests the possibility of improving the interfacial adhesion between the immiscible polymer blends containing the LCP by reactive extrusion processing with a very short residence time.

Mechanical properties of the blends were investigated in fiber form. The as-spun fiber tensile properties are summarized as shown in Table 4. These fibers were further drawn at elevated temperatures at various draw ratios. These drawn fibers were stronger than the as-spun fibers. Table 5 illustrates the effects of temperature and draw-ratio on the fiber properties. Drawing at 400 °C at a ratio... 

Table 5.12. Effect of extrusion temperature and draw-down ratio on mechanical properties of as-spun fibers of PET/60HBA and PET/80HBA. ...

The most important parameter controlling the final properties is the draw ratio, X. There is a direct relationship between X and the mechanical properties, in particular the modulus. The maximum draw ratio is generally limited to about 5 for PET and most PA s, about 10 for PP whereas values of 15-20 are common for HDPE. Crystallinity also has a strong effect on final properties. Strain-induced crystallization develops during the orientation process as the molecular order progressively increases upon drawing. 

The ribbon was placed between two split billet halves of the same polyethylene, and the assembly coextruded through conical brass dies which had an included entrance angle of 20 and nominal extrusion draw ratios, EDR, of 12, 25, and 30. No lubricant was used. The EDR calculated from the displacement of the line mark was in good agreement with the nominal EDR defined as the ratio of entrance to exit cross-sectional area of a die. The extruded films were used only for the evaluation of the effect of deformation components on the resultant morphology and properties. The semiperipheral coextrudates obtained simultaneously from the extruded assembly were used for the x-ray study of the deformation mechanism for extrusion drawing. 

DTA was used [31] to determine the melting temperature (r ), the heat of fusion AHm) and the degree of crystallinity (%C). PLLA with draw ratios of 3 1 to 8 1 exhibits good tensile properties. Crystallinity affects the mechanical properties and DSC was used [31] to consider the effect of the draw ratio on the crystallinity and, ultimately, the tensile strength of the fibres. 

The mechanical properties are usually determined from stress-strain tensile curves. Figure 3 shows the tensile strength and modulus in the most highly drawn direction as a function of the effective draw ratio in that direction. The data are taken from different papers involving different types of PP and different processing techniques. In spite of this wide range, the trend can be clearly seen. Undrawn PP has a modulus... 

Microfibrils Reinforced Composites Based on PP and PET Effect of Draw Ratio on Morphology, Static and Dynamic Mechanical Properties, Crystallization and Rheology... 

The conspicuous feature of the current study is that storage and loss moduli, and mechanical loss factor of the MFCs prepared at different draw ratios are compared with those of neat PP and neat blend. To the best of our knowledge, no reports have been published pertaining to the effect of draw ratio on the dynamic mechanical properties of the MFCs. 

Enhancement of the oxygen barrier properties of polyolefin films, combined with the improvement of their mechanical properties, is one of the most promising areas of current MFC research. This chapter focuses on both quantitative and qualitative research into the permeability of both MFCs and plain films. It contains explanations of the basic principles of permeability measurement and calculation followed by two investigations into the effects of PET content and drawing ratio. An experimental design provides conclusive evidence regarding the effects of several manufacturing parameters, as well as information on film crystallinity levels and permeability over time. In summary, these should be mentioned ... 

Table 8.9 Effect of Draw-down Ratio on Mechanical Properties of As-Spun Fibers of PET/60 HBA and PET/80 HBA. ...

---