ANTIOXIDANT DEPLETION AND OIT VALUES OF HIGH IMPACT PP STRANDS

The service life of a polyolefin product depends to large extent on the type and amount of the antioxidants added. During the manufacturing,storage and use of the product the antioxidants are depleted by physical processes and chemical degradation,and this impairs its long-term performance.The initial and in-use oxidation stability is often characterized and monitored by the measurement of the oxidative induction time(OIT),and service life predictions are based on the rate of decrease of the OIT value.To study the correlation between the OIT value and the actual antioxidant concentration,eight random arrays of high-impact polypropylene(PP)strands stabilized using six different antioxidant packages(composed of Irgafos 168,Irganox 1010 and 1330,Chimassorb 944)were immersed in hot water(80℃and 90℃)and oven aged in air (80℃)for more than two years,and the change of OIT values and antioxidant concentrations was measured.For phosphitic and phenolic stabilizers water immersion is generally a more critical aging condition than oven aging in air,while for the hindered amine stabilizers(HAS)the opposite was observed.As expected,a linear correlation between OIT values and concentrations was found for the'classical'package of phosphitic and phenolic stabilizers.In the case of Irganox 1330,the change of the OIT values during aging was considerably slower than the change of concentration.Even when zero concentration was reached according to the vanishing peak height in the chromatogram,a considerable OIT value was still measurable.This may be due to unidentified degradation products of Irganox 1330 which still act as antioxidants in the long run.Addition of HAS(Chimassorb 944)seems to enhance the initial OIT of stabilized phenolic samples and the long-term effectiveness of the phenolic stabilization under air oven aging conditions.However,the marked long-term effectiveness of the HAS itself and the slow change with time of the concentration were not detectable by OIT measurements above the PP melting point of about 170℃.

An Activatable Nanoenzyme Reactor for Coenhanced Chemodynamic and Starving Therapy Against Tumor Hypoxia and Antioxidant Defense System

It is critical to improve the efficiency of cancer therapy with minimized side effects.Chemodynamic therapy(CDT)is a tumor therapeutic strategy designed to generate abundant reactive oxygen species(ROS)at tumor sites through a Fenton or Fenton-like reaction.Recently,this developing scheme has demonstrated an incredible promise for tumor therapy.The process involved could induce cell death without the input of external energy,and this could only occur via the conversion of hydrogen peroxide(H_(2)O_(2))to hydroxyl radicals(·OH).Although Fenton or Fenton-like reactions are being exploited for CDT,along with an application of oxidation reactions to supplement H_(2)O_(2),it has been proven that in cancer cells,the high levels of the existing antioxidants could suppress CDT via·OH depletion,and,unfortunately,tumor hypoxia also inhibits the oxidation reactions.Herein,the authors aimed to fabricate an activatable nanoenzyme reactor(NER)to solve this challenge.Fluorescent reporters(FRs)and bioenzyme glucose oxidase(GOX)were coassembled on nanozyme MnO_(2) nanosheets,which was enwrapped by the tumor-targeting material,hyaluronic acid(HA).NER was internalized explicitly by cancer cells through ligand/receptor recognitionmediated endocytosis,followed by intracellular hyaluronidase(HAase)-dependent activation.As a result,the oxygen level was improved,and the antioxidants were depleted,leading to the promotion of glucose consumption and an increase in·OH level.Thus,the NER exhibited multiple effects to induce coenhanced,chemodynamic and starving therapy against tumor hypoxia and antioxidant defense system to achieve a favorable targeted tumor therapeutic,via these rigorously highly effective,and targeted biochemical reactions both in an in vitro cultured cancer cells systemor in an in vivo mice tumor model.