The region of frictional slip ΔT of spun yarns. has been suggested by J.W.S. Hearle, P. Grosberg and S. Backer. An attempt is made to determine continuously and objectively values of frictional slip ΔT by using an untwisting and drafting system developed by anthors for the rearrangment of fibers in open-end yarns.
The system is constructed with two pairs of rollers ; feed rollers and delivery rollers, and with one set of rotor fitted between the two pairs of rollers to untwist a yarn falsely. The surface velocity of the delivery roller is slightly higher than that of the feed roller.
In this system, the twist density between, the feed roller and the rotor is reduced to T-R, where T is a number of twist of a yarn and R is a number of untwisting by mechanical operations. If the value of T-R is very small, the yarn tension may be reduced to nearly zero. Assuming that the yarn tension is zero when the value of T-R is within the range of ΔT^*/2≤T-R≤ΔT^*/2, relation between the relative frequency of the zero tension of the yarn Z (R) and the probability density function of the yarn twist density n (T) is given by :
Z (R) =∫^R+ΔT*/2_R-ΔT*/2n(T)dt
Z (R) can be measured by using the untwisting and drafting system, and n (T) is determined by untwisting and twisting method. Then, the values of ΔT^* are caluculable by the equation above.
The experimental results are as follows :
(1) The linear relation is found between ΔT and ΔT^*.
(2) ΔT is not constant throughout the sample of yarn, i. e., the more twisted parts of the yarn shows the smaller value of ΔT^* and vice versa.
(3) Many kinds of yarns with the same material but produced by different spinning operations, show the general rule that under certain limiting condition for ΔT^* the stronger yarn shows the smaller mean value of ΔT^*.

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This paper reports the effect of solvent properties on the temperature at which nylon 6, polyethylene terephthalate (PET) and polypropylene begin to shrink in about thirty kinds of organic solvents.
An assumption is made that a decreasing effect of shrink-starting-temperature (T₁) caused by an absorbed solvents can be represented by a parameter ΔT₁/Q : where, Q is a degree of swelling and ΔT₁ is a difference of T1 between before and after solvent absorption.
The test results are that :
(1) decreasing effects ΔT₁/Q increases with decreasing molecular weight or molecular volume of absorbed solvents,
(2) if absorbed solvents are same in molecular weight or molecular volume, decreasing effect ΔT₁/Q of nonpolar solvents is higher than that of polar solvents, and
(3) decreasing effect ΔT₁/Q of solvents of noncoplanar structure is lower than that of solvents of coplanar structure.

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To determine the beauty of a crimp shape in crepe fabrics, the form of wet hard twist yarns caused by balancing a retractive fovce against untwisting torques has been analysed and the following conclusions have been obtained :
1) The. size of crimps is closely related to the numbers of spiral circles, which is given by the following equation :
m=0.2T/(1-f (s))
where m : the numbers of spiral circles,
T : yarn twist in turns per unit length, f (s) : the shrinkage of crepe fabrics when wetted.
2) The amplitude of crimp is related to the radius of spiral circle r, which is given by the following equation :
r=√1- (1-f (s)) ²/0.4πT
3) The thickness of crepe fabrics is propotional to the radius of spiral circles and is greatly influenced by the twist multiplier of hard twisted yarns.
4) The degree of crimp, C_a-1 is a function of fabric shrinkage and is given by the following equation :
C_a-1=A·f (s) ^5/2
where, A is an experimental constant determined by the arrangement of weft yarns.

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