Evaluation of the stability of rigid poly(vinyl chloride)/biologically active phthalimido phenyl urea composites using thermogravimetric analysis

Four novel phthalimido phenyl urea derivatives, prepared by a low temperature solution condensation reaction between N-[4-(chlorocarbonyl) phenyl] phthalimide and either of phenyl urea, p-methyl phenyl urea, o-chloro phenyl urea or p-carboxy phenyl urea, have been investigated as antimicrobial thermal stabilizers for rigid PVC. They were characterized by FTIR, 1H-NMR, mass spectra, elemental analysis and antimicrobial activity. Their antibacterial activities against Bacillis subtilis and Streptococcus pneumoniae as Gram-positive bacteria and against Salmonella typhimurium as Gram-negative bacteria and their antifungal activities against Aspergillus fumigatus, and Geotricum candidum were evaluated using the agar well diffusion technique. The results indicated that these derivatives showed good antibacterial activity as judged by their high inhibition zone diameter and low minimum inhibition concentration. These derivatives are more potent against Gram-positive bacteria than against Gram-negative bacteria. The results also indicated that these derivatives have effective antifungal activity. The carboxy derivative exhibited the highest antimicrobial activity relative to the other derivatives. Their stabilizing efficiency is evaluated using thermogravimetric technique in nitrogen, and by the extent of discoloration as well as by the change in the molecular weight of the degraded polymer. The results reveal the greater stabilizing efficiency of these derivatives relative to dibasic lead carbonate (DBLC), cadmium-barium-zinc (Cd-Ba-Zn) stearate complex and di-n-octyltin bis (isooctylmercaptoacetate) (n-octyltin mercaptide, n-OTM) reference thermal stabilizers. This is well illustrated by the higher initial decomposition temperature, and lower rates both of weight loss and discoloration as well as decreasing in degree of chain scission of the polymer during degradation relative to those of the reference stabilizers. Moreover, the stabilizing efficiency is influenced by the nature of the substituent group in the aryl moiety of the phenyl urea part of these derivatives. While, the methyl derivative is characterized by a greater efficiency relative to those of the chloro and carboxy derivatives, the non-substituted derivative lies between these two cases.