- The cause of poor thermal stability of the synthetic fiber fabric.
(1) The internal stress is hidden during the fiber forming process, and the arrangement of the macromolecules does not reach the most stable state. When the heat is heated, the molecular thermal vibration is intensified, and the bending occurs, so that the fabric is retracted and the size is reduced.
(2) The continuous force in the textile process, and the uneven force, which aggravates the tendency of heat shrinkage and unevenness of retraction, causes wrinkles in the fabric, and is difficult to remove.
- Heat setting method
That is, the heat energy of the fabric is supplied under appropriate tensile tension, the large portions are rearranged, and then rapidly cooled, so that the fibre is in a stable state with lower energy.
The process is divided into three phases:
(1) Relaxation stage of macromolecule: When heated to above Tg, the interaction between the molecular chains is ↓, the internal rotation of the macromolecule is ↑, the flexibility is ↑, the degree of orientation is ↑, and the internal stress is ↓.
(2) Segment reorganization stage: With the thermal vibration of the macromolecular chain, the active groups meet each other, and it is easy to establish a new intermolecular force. If tension is applied, the macromolecules are rearranged according to the tension direction to establish a new balance.
(3) Styling stage: The temperature is lowered before the external force is removed, and the fifix is fixed in the new form.
- Changes in fiber structure during heat setting
The thermosetting T is between Tg and Tm (melting point refers to the larger and complete crystallization melting T in fibre). At Tg, the atoms and groups in the molecular chain vibrate in the equilibrium position, and begin to move with the displacement of the chain segment, and with T_and_, the displacement of the whole macromolecular chain begins to occur after reaching Tm. Fibers contain crystals of different sizes and completeness and have different melting points.
When thermal setting is carried out under T1 (& lt; Tm), some crystals with small size and poor integrity melt, and relatively uniform and large crystals increase or more complete, thus bringing crystallinity, grain size and integrity distribution to a new state. At this time, after relaxation heat treatment on T1, the number of crystals that fibre can melt_dimensional thermal stability, dyeing performance, stiffness and elasticity also change.
The setting mechanism of acrylic fibers is different from that of polyester fibers.
Thermosetting results in the rearrangement of macromolecules in the amorphous region of acrylic fibers due to the intensification of thermal motion, the elimination of internal stress, and the reconstruction of some more solid new bonding points, which improves the integrity of the crystallization zone and thus improves the thermal stability of fibre.