Structure and Drawability of Polypropylene Fibers in the Direct Spin Draw Process Equipped with the Cooling Take-up Roll

In the field of nylon and polyester fibers, there has been a tendency in recent years for the Direct Spin Draw (DSD) process to become the mainstream technology. However, in the case of Polypropylene (PP), fibers with high tenacity could not be obtained using the DSD process because PP fibers could not be drawn to high draw ratio. To solve this problem, a new DSD (I-DSD) process was developed. In this process, a contact-type cooling take-up roll was installed after the melt spinning stage and an as-spun fiber was drawn after it was force cooled. It was possible to effectively control the crystallinity of as-spun fibers and increase the maximum draw ratio of the fiber to as high as 9 even when drawing was carried out on an in-line basis. This high draw ratio was almost equal to that obtained in the Offline Drawing (OFD) process. In addition, it was found that as-spun fiber with lower crystallinity had a higher maximum draw ratio. A negative correlation coefficient between the crystallinity and the maximum draw ratio of as-spun fiber was found for the I-DSD process.