Orientation of polymer molecules during melt spinning. II. Orientation of crystals in as‐spun polyolefin fibers

A basic investigation of the development of crystallization and orientation during the melt spinning of syndiotactic and isotactic polypropylene is described. Both polymers were melt spun through ambient air or into ice water at various draw-down ratios and melt temperatures. The melt spun ®laments were characterized by wide angle x-ray diffraction (WAXD), birefringence and differential scanning calorimetry (DSC). The polymorphic behavior of isotactic polypropylene during melt spinning is well known. The ®laments melt spun through ambient air exhibit the monoclinic a-form while the ®laments melt spun into ice water form a smectic structure at low draw-down ratios. Syndiotactic polypropylene also exhibited polymorphic behavior during melt spinning. Disordered Form I with (t 2 g 2 ) 2 helices was found at low spinline stresses and Form III with all trans chain conformation was found at high spinline stresses. The criterion of the spinline stress for this transition was found to be about 6±9 MPa for all samples of various molecular weights, melt temperatures and cooling rates. Syndiotactic polypropylene crystallized much more slowly than isotactic polypropylene and did not exhibit a smectic mesomorphism under ice-water quenched conditions. The melt spun ®laments of syndiotactic polypropylene exhibited lower birefringences and amorphous orientations but higher crystalline orientations than those of isotactic polypropylene, compared at the same spinline stresses.

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“…The crystalline orientation was expressed in terms of the Hermans-Stein orientation factors [24,26,28,31,32,36], which are de®ned as…”

Section: Fiber Characterizationmentioning

confidence: 99%

Structure Development in Melt Spinning Syndiotactic Polypropylene and Comparison to Isotactic Polypropylene

Choi

White

2000

International Polymer Processing

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“…(3), (4), and (5) at each point on the spinline. The value of F(0) was estimated from the elongational viscosity of polypropylene as a function of temperature and molecular weight using the data of Minoshima et al15 Equation (2) was then used to compute values of F(z), and spinline stress was obtained by dividing F(z) by the filament cross-sectional area.…”

Section: Computation Of Spinline Stressesmentioning

confidence: 99%

The influence of resin characteristics on the high speed melt spinning of isotactic polypropylene. II. On‐line studies of diameter, birefringence, and temperature profiles

Lü

Spruiell

1987

J of Applied Polymer Sci

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synopsisAn investigation was carried out of the high speed melt spinning of three polypropylene resins with melt flow indices of 12, 35, and 300. On-line measurements were made of +ameta, birefringence, and temperature as a function of distance from the sphneret for a range of spinning conditions for each polymer. A plateau (decrease of cooling rate) in the temperature profile was associated with the Occurrence of crystallization in the spinline. The position of this plateau correlated with a rapid rise in the birefringence profile and a rapid decrease in the rate of drawdown in the diameter profile. The temperature and birefringence profilea were used to determine the temperature and position on the spinline at which the onset of crystallization occurred. It was found that the position and temperature of crystallization onset varied considerably with changes in takeup velocity, extrusion temperature, and resin melt index (weight average molecular weight). The crystallization onset occurred nearer the spinneret and at higher temperatures with (1) an increase of take-up velocity, (2) a decrease of extrusion temperature, or (3) a decrease of reain melt flow index. An analysis was carried out to estimate the rate of stress development with distance along the spinline; the reaults were also used to estimate the stress at the onset of crystallization for each spinning condition. It was concluded that the observed behavior could be attributed to the role of spinline stress in producing molecular orientation and consequent increase of crystallization rate.

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“…The polyethylene copolymers considered in this study, summarized in Table I, are four in number, with densities varying from 0.870 to 0.958 g/cm 3 . S-2, S-3, and S-4 are ethylene-octene copolymers prepared by Dow's Insite constrained geometry catalyst (CGCT) and process technology, which can impart a material narrow molecular weight distribution, homogeneous comonomer distribution, and a controlled branching structure.…”

Section: Methodsmentioning

confidence: 99%

Structure development in melt spinning of poly(ethylene‐co‐octene) filaments with various comonomer contents

Shan

White

2004

J of Applied Polymer Sci

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An experimental study of the spinnability and the variation in crystallinity and orientation of melt spinning of poly(ethylene-co-octene) with different contents of comonomers was carried out. The spinning behavior of these polymers was investigated under different drawdown ratios and temperatures and correlated to spinline stress. The melt-spun filaments were characterized by wideangle X-ray diffraction birefringence, and differential scanning calorimetry. S-1 is a high-density polyethylene and S-2, S-3, and S-4 have 16, 22, and 38 wt % octene. An orthorhombic unit cell was found in all four polymers, but a dominant hexagonal structure (perhaps mesophase) was found for the highest octene level (S-4). The orientation factors for the a-, b-, and c-axis of the orthorhombic crystal structure and a-axis of the hexagonal phase were then calculated. The crystalline orientation behavior of the lower octene copolymers (S-1, S-2, and S-3) are similar and can be represented as a "rownucleated" structure. However, the orientation behavior of S-4 was different. The uniaxial mechanical properties were also measured. The Young's modulus and tensile strength generally increased with birefringence for all polymers. With increasing content of octene, the Young's modulus showed a decrease from semicrystalline thermoplastic toward an elastomer.

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Orientation of polymer molecules during melt spinning. II. Orientation of crystals in as‐spun polyolefin fibers

Cited by 54 publications

References 15 publications

Structure Development in Melt Spinning Syndiotactic Polypropylene and Comparison to Isotactic Polypropylene

Structure Development in Melt Spinning Syndiotactic Polypropylene and Comparison to Isotactic Polypropylene

The influence of resin characteristics on the high speed melt spinning of isotactic polypropylene. II. On‐line studies of diameter, birefringence, and temperature profiles

Structure development in melt spinning of poly(ethylene‐co‐octene) filaments with various comonomer contents

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