Seiji Endo

The flame-retardant polyester fiber: Improvement of hydrolysis resistance

As far as the flame-retardant polyester fibers are concerned, the copolymerization of phosphorus retardants is the most common method. But a serious problem is that the phosphorus-containing polymer is easily hydrolyzed. We investigated the flame retardancy and the hydrolysis properties of two poly(ethylene terephthalate) (PET) fibers, one with a phosphorus compound as a side chain (side-chain type: HEIM® Toyobo Co., Ltd.), and one with a phosphorus compound inserted in the polymer backbone (main-chain type). Both types had almost the same properties of fibers and flame retardancy, but the main-chain type was hydrolyzed about two times faster than the side-chain type, and led to a decrease of toughness immediately. This difference of hydrolysis properties between main-chain type and side-chain type depends on whether a phosphonate ester bond is placed in the polymer backbone or the pendant site. In the case of the main-chain type, the scission of the polymer backbone chain occurs by hydrolysis of phosphonate ester bonds; however, in the case of the side-chain type, this does not occur. These results demonstrate that the flame-retardant polyester fiber with the side-chain type modifier gives sufficient flame retardancy and excellent hydrolysis resistance.

Synthesis and characterization of poly(oxy-2,6-naphthalenediylcarbonyl) whiskers from 2-acetoxy-6-naphthoic acid

Abstract The synthesis and characterization of poly(oxy-2,6-naphthalenediylcarbonyl) (PON) whiskers from 2-acetoxy-6-naphthoic acid are described. The important factors in controlling PON crystal morphologies during high-temperature solution polymerization are polarity of solvent, concentration of monomer and stirring. Less-polar solvents like liquid paraffin or Therm S 800, low concentration of monomer and no stirring are desirable for making PON whiskers. The size of the whisker prepared in liquid paraffin is 7–17 μm in length and 0.5-1.0 μm in width. From its electron diffraction patterns, it was found that this whisker exhibits a single-crystal nature and the polymer chains align along the long axis of the whisker. Owing to the close packing of polymer chains in this crystal, the whisker has the highest thermal stability compared with the other fibrillar and slab-like crystals. The formation mechanism of PON whiskers is also investigated in comparison to that of poly(oxy-1,4-benzenediylcarbonyl) whiskers.

Solvent effect on the morphology of poly(oxy-1,4-benzenediylcarbonyl) whiskers from p-acetoxybenzoic acid

Abstract Poly(oxy-1,4-benzenediylcarbonyl) (POB) whiskers from p -acetoxybenzoic acid were prepared in mixtures of liquid paraffin having many branched carbons (LP) and completely linear paraffin (SW). The crystal shapes of the POB whiskers obtained were largely changed by the mixing ratio of LP and SW. When the content of SW in the solvents increased: (i) both the length and the width of the whiskers decreased; (ii) the tip angle of the whiskers increased; and (iii) radial growth of the whiskers increased. The size of the POB whiskers was attributed to both the number and the size of those lamellar crystals with screw dislocations (primary nuclei for whisker growth) which had formed in the early stages of polymerization. In SW, larger numbers of smaller lamellar crystals were formed than in LP, owing to the lower solubility of POB oligomers at 330°C in SW; that is, the higher supersaturated state of the POB oligomers produced a larger number of smaller primary nuclei for whisker growth. Hence, whiskers having smaller lengths and widths were obtained as the content of SW increased. The other characteristic changes in whisker shapes, i.e. tip angles and radial growth, also seemed to be attributable to the degree of supersaturation of the POB oligomers, though further study is required. The thermal properties of the whiskers were evaluated by differential scanning calorimetry and thermogravimetric analysis.