Figure 4. DTA patterns of PPS-based bag filter materials with different loading units.
As a key indicator for the semi-crystalline of PPS, the melting point (Tm) could reflect intuitively its crystalline characteristics[27]. DTA patterns of pure PPS and fifteen samples collecting from factories were conducted by a thermal analyzer system and summarized in Fig. 4. It can be observed that Tmreduces progressively and the width of peak of melting point becomes broaden with increase of content of SO2 for all categories regardless of loading unit (below 200 MW, 200-300MW and above 300 MW). Generally, crystal is an ordered arrangement of molecular chains, while the melting destroys the assembly structure of molecules wholly to form the disordered molecular chain[27, 35]. Higher crystallinity of polymer is, more regular of arrangement of molecular chains is, and higher temperature to destroy its assembly structure needs, and thus higher the melting point gets for the same material. The appearance of new functional groups including -SO-, -SO2- and -SO3H in the molecular chain of PPS would break its structural regularity along with the decreasing of crystallinity, and reduction of melting point of fifteen samples can be explained. Besides, the lower of melting point is, the more serious damage of crystal is, and thus the lower of crystallinity is for the same material. Therefore, the crystallinity of PPS gradually declines with the addition of content of SO2 from 1# to 5#, 6# to 10# and 11#-15#, which is in good agreement with those obtained from the SEM and FTIR analysis.
3.3 Mechanical properties of PPS-based bag filter materials
As a crucial index to evaluate superiority or inferiority of mechanical properties of PPS-based bag filter materials during the running of the filter bag, CD strengths of all samples were introduced and shown in Fig. 5.