Spin Trapping Analysis of Radical Intermediates on the Thermo-Oxidative Degradation of Polypropylene.

The purpose of this study is to investigate the thermo-oxidative degradation behavior of polypropylene (PP) by comparing three types of pristine PP granules (consisting of homopolymer, random copolymer, and block copolymer) with their corresponding oxidized analogues. These analogues were intensely oxidized under oxygen at 90 °C for 1000 h by using the electron spin resonance (ESR) spin trapping method that can detect short-lived radical intermediates during the degradation. The degrees of oxidation could be evaluated by chemiluminescence (CL) intensity, which was related to the concentration of hydroperoxide groups generated in the PP chain. In the pristine PP samples, a small amount of hydroperoxides were found to be formed unintentionally, and their homolysis produces alkoxy radicals, RO•, which then undergo ß-scission to yield chain-end aldehydes or chain-end ketones. These oxidation products continue to take part in homolysis to produce their respective carbonyl and carbon radicals. On the other hand, in the oxidized PP granules, because of their much higher hydroperoxide concentration, the two-stage cage reaction and the bimolecular decomposition of hydroperoxides are energetically favorable. Carbonyl compounds are formed in both reactions, which are then homolyzed to form the carbonyl radical species, •C(O)-. PP homopolymer produced the largest amount of carbonyl radical spin adduct; thus, it was found that the homopolymer is most sensitive to oxygen attack, and the presence of ethylene units in copolymers enhances the oxidation resistance of PP copolymers.

Polyethyleneimine-crosslinked cellulose aerogel for combustion CO2 capture.

Polyethylenimine (PEI) will block the channel of pore when it was impregnated in the porous solid, limiting its practical application in CO2 adsorption. In this method, a novel polyethyleneimine-crosslinked cellulose (PCC) aerogel sorbent was prepared by the sol-gel process, hydrolysis reaction and crosslinking reaction. The specific surface area of porous PCC aerogel was still retained 234.2 m2/g when the content of nitrogen was 17.4 wt%. The CO2 adsorption capacity of PCC aerogel reached 2.31 mmol/g at 25 ℃ under pure dry CO2 atmosphere. Pseudo-second order model perfectly is suitable to predict the CO2 adsorption behaviors of PCC aerogel at different temperatures. The CO2 diffusion mechanism of PCC aerogel was limited by not only intra-particle diffusion but also surface diffusion. The PCC aerogel showed excellent CO2 adsorption-desorption recyclability after 10 cycles. This work proved that the PCC aerogel played an important role as a potential CO2 adsorption solids.

Irradiation of cellulosic pulps: understanding its impact on cellulose oxidation.

Different pulp samples were irradiated by three energy sources: plasma, electron beaming, and γ radiation. The effect of increased exposure to irradiation was studied by multidetector gel permeation chromatography with fluorescence labeling of carbonyl groups to quantify changes of the cellulose. Whereas plasma treatment had no effect, for gamma and electron beam the degradation primarily affects the high molar mass area. Kinetic calculations based on DPw were performed. They show close-to-linear relations with slopes in the same order of magnitude, suggesting that wood-derived pulps degrade slower than pulps from annual plants. The rise in carbonyl group content is linear with increasing dose. In particular, in pulps from annual plants, most detected carbonyl structures originate from the new reducing end groups. Therefore, oxidative modification of cellulose molecules by means of radiation appears to be viable for pulps produced from wood. Here the increase in oxidized functionalities is partially disconnected from chain scission.

Effect of electron beam irradiation on the structure and properties of electrospun PLLA and PLLA/PDLA blend nanofibers.

Poly(L-lactide) (PLLA) and a PLLA/poly(D-lactide) (PDLA) blend (50/50 wt.%) were electrospun into nanofibers. Electron beam (e-beam) irradiation of the electrospun PLLA and blend nanofibers was used as a method to alter their structures and surface properties. The crystalline structures of the nanofibers before and after irradiation were investigated by differential scanning calorimetry. Tensile tests of the aligned nanofibers were also performed to determine the effects of irradiation on the mechanical properties of the nanofibers. The hydrophilicity of the nanofibers was determined by water contact angle measurements, while any degradation of the fibers caused by irradiation could be detected by intrinsic viscosity measurements. The e-beam irradiation method was able to improve the surface hydrophilicity of the PLLA and blend nanofibers, although bulk degradation was inevitable.