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Despite its commercial success, isotactic polypropylene (PP) is not suitable for the applications that require long-term exposure to high-energy conditions, such as elevated temperatures, UV radiation, or high electric fields, due to the combination of polymer chain oxidative degradation, incompatibility with polar additives (antioxidants, stabilizers, etc.), and low material softening temperature. This paper presents a new solution that can simultaneously address both chemical and physical limitations. The idea is to develop a new PP-HP copolymer that contains some specific hindered phenol (HP) groups, homogeneously distributed along the polymer chain. These PP-bound HP pendant groups can not only effectively protect PP chains from the oxidative degradation but also engage in a facile cross-linking reaction to form a 3-D network structure during the oxidation reaction. One accelerated oxidation test in air at 190–210 °C shows this distinctive advantage. While a commercial PP polymer (containing common antioxidants and stabilizers) degrades within 1 h, a PP-HP copolymer with about 1 mol % (9 wt %) HP groups shows almost no detectable weight loss after 1000 min. In an ASTM endurance test under a targeted application temperature (140 °C in air), the commercial PP shows 1% weight loss within about 10 days. On the other hand, this new PP-HP lasts for 105 days (4 order increase) under the same condition. In the strain–stress curve measurement, the PP-HP film also shows no detectable change in tensile strength and modulus after constant heating the polymer film at 140 °C in air for 1 week. Overall, the experiment results present the potential of expanding PP applications into a much higher temperature range (>140 °C) under oxygen oxidative environments.

The aim of this work was to develop well dispersed nanocomposites, in a non water soluble polymer using a non aqueous, low polarity solvent as a dispersion medium. The nanoreinforcements were cellulose whiskers and layered silicates (LSs) and matrix was cellulose acetate butyrate (CAB). Before nanocomposite processing, a homogenizer was used in combination with sonification to achieve full dispersion of the nanoreinforcements in a medium of low polarity (ethanol). After processing, the cellulose nanowhiskers (CNW) showed flow birefringence in both ethanol and dissolved CAB, which indicated well dispersed whiskers. The microscopy studies indicated that the processing was successful for both nanocomposites. The CNW showed a homogeneous dispersion on nanoscale. The LS nanocomposite contained areas with lower degree of dispersion and separation of the LS sheets and formed mainly an intercalated structure. The produced materials were completely transparent, which indicated good dispersion. Transparency measurements also indicated that the nanocomposite containing CNW showed similar performance as the pure CAB. Dynamic mechanical thermal analysis (DMTA) showed improved storage modulus for a wide temperature range for both nanocomposites compared with the pure CAB matrix. This study indicated that CNW have a potential application in transparent nanocomposites based on fully renewable resources. V

Currently, hindered phenol (HP) antioxidants mixed in PP products provide thermal-oxidative protection during PP melt processing (homogeneous mixing). However, there are concerns about their effectiveness during applications. This paper presents computer simulation and experimental results to demonstrate a facile phase separation of HP molecules in the PP matrix and investigates a new approach that can dramatically improve PP thermal-oxidative stability under elevated temperatures. This technology is centered on a new PP–HP copolymer containing a few comonomer units with HP moieties, homogeneously distributed along the polymer chain. Because of the cocrystallization between the PP and PP–HP copolymer, all HP antioxidant groups are homogeneously distributed in the PP matrix (amorphous domains). The resulting PP/PP–HP blends demonstrate a thermal-oxidative stability nearly proportional to the HP content. While commercial PP products (containing regular antioxidants and stabilizers) degrade within a few minutes at 210 °C in air, the PP/PP–HP blend, with the same concentration of HP groups, demonstrates nearly no detectable weight loss after 1000 h. In an ASTM endurance test under a targeted application temperature (140 °C in air), the commercial PP shows 1% weight loss within 10 days. On the other hand, the new PP/PP–HP (5/1) blend with the same HP content lasts for about 2 years under the same constant heating condition. Overall, the experiment results of the PP–HP antioxidant present the potential of expanding PP applications into a far higher temperature range (>140 °C) under thermal-oxidative environments.