SYNOPSISThe role of molecular weight distribution on the spinnability, structure, and properties of melt-spun isotactic polypropylene filaments was studied with the aim of clearly distinguishing the effect of the breadth of the distribution from the effect of the average molecular weight and resin melt flow rate (MFR). Nine resins were chosen for this purpose, ranging in MFR from 16 to 78 and in polydispersity from 2.6 to 5.4. It was observed that the spinnability, structure, and properties of the spun filaments were all strong functions of the breadth of the distribution. Spinnability decreased with increasing breadth. At given spinning conditions and polydispersity, an increase in the weight-average molecular weight (decrease in MFR) produces an increase in crystallinity, birefringence, tensile strength, and tensile modulus. But at given spinning conditions and resin MFR, broadening the molecular weight distribution (increasing the polydispersity) produces an increase in crystallinity, tensile modulus, and elongation-to-break while birefringence and tensile strength decrease. The major influence of the polydispersity on the structure and properties developed was attributed to its effect on both the elongational viscosity of the resin and the ability of high molecular weight tails in the distribution to influence the stress-induced crystallization that occurs in the spinline. 0 1995 John Wiley & Sons, Inc.
SYNOPSISThe influence of isotacticity, ethylene comonomer content, and nucleating agent additions on the structure and properties of melt-spun polypropylene filaments was studied for a series of polypropylenes having similar resin melt flow rates (MFR z 35), average molecular weights, and polydispersities. In general, increasing the degree of isotacticity increases crystallinity and tensile modulus of the spun filaments, while increasing the copolymer content has the opposite effect. Nucleating agent additions also lead to greater crystallinity, but, under certain conditions, the addition of a nucleating agent can lead to lower tensile modulus in spite of higher crystallinity. For given spinning conditions, the tensile strength increased slightly with increased copolymer content but was little affected by tacticity in the range studied. Nucleating agent additions lowered the tensile strength of spun filaments. The effects of nucleating agents on the filament modulus and tensile strength were traced to their ability to raise the crystallization temperature and reduce the level of molecular orientation generated in the filaments. The reasons for the observed behavior are discussed. I N T R O D U CTlO NThis is the fifth paper in a series from our group dealing with the influence of resin characteristics on the structure and properties of melt-spun isotactic polypropylene filaments. Three of the earlier papers'-3 dealt extensively with the influence of molecular weight and polydispersity and the interaction of these variables with the spinning process variables. It was shown that the processing, structure, and properties of polypropylene filaments are highly influenced by both molecular weight and polydispersity. A fourth paper4 briefly examined the effects of changing the crystallization kinetics by adding a
SynopsisElastic filaments have been produced by melt spinning poly(tetramethy1ene terephthalate)/ poly(tetramethy1ene ether glycol)-terephthalate (PTMT/PTMEG-T) copolymers of various hard segment contents (HSC). Some of these copolymers are difficult to spin because of their elastic nature and sluggish crystallization kinetics. Differential scanning calorimetry studies show that both the crystallization rate and temperature decrease as HSC decreases. When spinning into air, the filaments low in HSC do not crystallize on-line and are too tacky and soft to be taken up with a conventional constant tension winder. The elastic nature of these filaments prevents them from being taken up at speeds high enough for "stress-induced crystallization" to cause appreciable crystallization on-line. Spinning into a water bath allows the filaments to be taken up without a "sticking" problem. The microstructure and mechanical properties of the water-quenched filaments were found to be strongly dependent on composition and processing conditions. Smallangle and wide-angle x-ray techniques (SAXS and WAXD) indicate that the hard segment domains are lamellar-like crystallites which become preferentially oriented perpendicular to the fiber axis at high spin-draw ratios. As HSC decreases, the lamellae become more widely spaced. High levels of crystalline orientation can be produced using the water quench technique without creating appreciable levels of amorphous orientation. These are desirable features for obtaining high elastic recovery. Birefringence results indicate that these filaments continue to crystallize for up to 10 minutes after spinning. The relative degree of phase separation (DPS) decreases as HSC increases, but the actual level of crystallinity exhibits a maximum with respect to composition. Not coincidentally, the filaments that reach the highest crystallinity are the easiest to spin. The modulus of these filaments depends primarily on HSC and DPS, while the tenacity and ultimate elongation depend more on the degree of orientation developed during spinning. Elastic recovery increases as HSC decreases and as crystalline orientation increases.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.