Effect of iron carboxylates on the photodegradability of polypropylene. I. Natural weathering studies

Abstract

To enhance the photodegradability of polypropylene (PP), various carboxylates of iron, including ferric caprate (MF03), ferric laurate (MF04), ferric myristate (MF05), ferric palmitate (MF06), and ferric stearate (MF07), were synthesized. Virgin PP was blended with the synthesized prodegradants (0.2%) and blown into films. To study the photodegradation behavior of PP with and without the prodegradants under natural weathering conditions, all of the films were exposed to sunlight according to the procedure of ASTM 1435. All of the weathered films were found to degrade after a certain number of days of exposure; this was found from the steep increases in the carbonyl, hydroperoxide, hydroxyl, lactone, ester, carboxylic acid, and crystallinity indices. At the same time, a sudden decrease in the elongation at break percentages and tensile strength and surface cracks were also observed. PP containing the prodegradants degraded at a faster rate than the virgin material. The time taken for the material to lose half of the elongation at break value was taken as the halftime, and this was used to determine the effectiveness of the prodegradants. The effectiveness of the prodegradants for the photodegradation of PP was found to be in the following order: MF03 > MF04 > MF05 > MF06 > MF07. With increasing alkyl chain length of the prodegradants, the stability of the alkyl radical increased, whereas the mobility of the radical in the PP matrix decreased.

Thermal characterization of the oxo-degradation of polypropylene containing a pro-oxidant/pro-degradant additive

“…Furthermore, a slight increase of the original crystalline content is also observed for pure PP during exposure to UV radiation (Table 1). It is well evidenced that the crystalline content of polypropylene increases at the beginning of oxidation [35][36][37]57,59,60,[63][64][65]. This phenomenon has been explained as due to chain scission, which initially is the major driving force of the oxidative process, and leads to increasing segment mobility and chain arrangements, favouring further crystallisation [58].…”

“…In contrast, studies on the abiotic [35][36][37][38][39] and biotic [40][41][42][43] degradability of polypropylene (PP) with pro-oxidant/pro-degradant additives are scarce as yet, although being this polyolefin one of the most widely used commodity polymers.…”

Microstructure studies of isotactic polypropylene under natural weathering by positron annihilation lifetime spectroscopy

“…A progressive decrease of M w for weathered PP with exposure time was observed, indicating that PP macromolecules gradually degraded into small molecule chains as exposure time prolonged. This result can be attributed to the PP chain scission reaction, such as Norrish type 1 and Norrish type 2 reactions [6,25]. Table 1 shows the polydispersity index (M w /M n ) of weathered PP bars withdrawn after different exposure time.…”

“…3b. The enhancement of the crytallinity index value with exposure time could be explained by the chain scission which releases previously entangled chain segments and enables them to crystallize, and the formation of new low-molecularweight oxidation species which are capable of conducting chemi-crystallization [25,30].…”

“…Carbonyl index that calculated as the ratio of the maximum absorbance at 1712 cm −1 to the absorbance at 974 cm −1 is the most used parameter for estimating the extent of PP degradation. In this work, the band at 974 cm −1 was chosen as reference peak, because it remains unchanged during the degradation process [25]. For exposed surface of weathered PP, the carbonyl index values show a notable increase with exposure time (Fig.…”