Thermo-oxidative Degradation Of Polypropylene Research Articles

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 β-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.

Biocatalytic Synthesis of a Novel Polyaniline Derivative and Its Usage for Polypropylene Stabilization

The synthesis, characterization, and some physical properties of a new polyaniline derivative (PHCA), produced by horseradish peroxidase (HRP) initiated oxidative polymerization of 2-hydroxy-5-chloroaniline (HCA), are presented. The spectroscopic measurements indicate that PHCA consists of a mixture of branched and linear aniline chain units. Data from antioxidant potential assays show that PHCA exhibits moderate 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity but excellent metal ion chelating ability. The metal chelating ability of PHCA (82.14 ± 2.39%) is about 2 times higher than that of EDTA (30.08 ± 0.81%) at a concentration of 100 μg/mL. In addition, as a potent antioxidant stabilizer, the influence of PHCA on the thermooxidative degradation of polypropylene (PP) is also investigated. The insertion of PHCA into PP matrix improves significantly both the oxidation induction time (OIT) and the onset oxidation temperature (OOT) of virgin PP.

The genesis of CO 2 and CO in the thermooxidative degradation of polypropylene

Using a set of three isotactic polypropylene samples that had been individually labeled with carbon-13 at each of the three positions in the monomer unit, we conducted experiments to determine the position of origin of carbon monoxide and carbon dioxide that arise during thermal oxidation of this polymer. By GC–mass-spectral analysis, we find that 2/3 of the CO 2 derives from the C(1) [methylene] carbon and the remaining 1/3 comes from the C(2) [tertiary] carbon, with none coming from the C(3) [methyl group] carbon. The CO also comes mainly from the C(1) [methylene] carbon (≥80%). This is in contrast to the solid-phase oxidation products, which have been found (by C-13 NMR on these same labeled PP materials) to originate predominantly (80–85%) from oxidation at the C(2) [tertiary] carbon. These results can be understood in terms of the free-radical reactions that underlie the polypropylene oxidation chemistry.

Effect of Phosphorus-Containing Fire-Retardant Systems on Fireproofing and Processing Indexes of Polypropylene

The thermal stability of polypropylene composites containing the microencapsulated ammonium salt of methylphosphonic acid amide and copper-zinc-boron compounds as a fire retardant was investigated. It was shown that incorporation of dizinc hexaborate increases the thermal stability period (MFI of 15 min) in comparison to this index for the composite containing a fire retardant alone (MFI of 2 min), which is due to slowing of decomposition of the fire retardant. It was found that dizinc hexaborate alters thermooxidative degradation of polypropylene containing microencapsulated methylphosphonic acid amide ammonium salt by decreasing the temperature and maximum rate of decomposition. The number of gaseous compounds liberated in thermooxidative decomposition of the composite is much lower than for the initial polypropylene.

Influence of environmental concentrations of ozone on thermo-oxidative degradation of PP

Recently it was postulated that natural variations of ozone concentration could have a big influence on the oven stability of polypropylene (PP). To examine this hypothesis the influence of low concentrations of ozone (comparable with environmental concentrations) on the thermo-oxidative degradation rate of PP-films was determined. PP-films were aged in a draft air oven with and without the addition of a small amount of ozone (maximum concentration ozone in the oven was 100–200 μg/m 3). The decrease of the elongation at break as function of oven ageing time was determined. It is shown that changes in the environmental concentrations of ozone have no significant influence on the rate of degradation in an oven.

Hindered amine stabilisers as long-term heat stabilisers for polypropylene

A comparison is made between the efficiency of hindered amine stabilisers (HAS) and phenolic antioxidants as stabilisers against the thermo-oxidative degradation of polypropylene (PP) and their ability to reduce the oxidation rates of decalin, squalane and decalin/lauraldehyde mixtures. The stabilisation mechanism of phenolic antioxidants differs from that of HAS. Phenolic AOs are able to stop the oxidation of model compounds and PP. They are effective until they are consumed. The effectiveness of HAS depends on the system into which they are incorporated. When aldehydes can be formed (squalane and PP) or are added (decalin/lauraldehyde mixture) HAS are more effective than in cases where aldehydes do not play a role (decalin). The results with squalane and decalin/lauraldehyde mixtures are comparable to those with PP. The best comparison is found for squalane.

Study of thermo-oxidative degradation of molten state polypropylenes with a variety of tacticities

Thermo-oxidative degradation of polypropylene(PP)s with a variety of tacticities was investigated in terms of various degradation factors, such as catalyst residue in the PP and molecular weight of the PP. Heat treatment was typically carried out in air at 200°C for 30 min, where the PP powder was converted to a molten state within several minutes. The catalyst residue and molecular weight had a slight influence on the thermo-oxidative degradation of isotactic PP (iso-PP). The thermal stabilities of three PPs [iso-PP, atactic PP (ata-PP), and syndiotactic PP (syn-PP)] having similar molecular weights were investigated under the same conditions. Iso-PP was degraded drastically in air compared with ata-PP and syn-PP. Thus, it was found that the influence of the tacticity was significant compared with that of the catalyst residue and molecular weight.

The role of peroxides in the thermooxidative degradation of polypropylene

The nature of the peroxides formed during thermooxidative degradation of polypropylene is still a subject of discussion. It is clear that these peroxides consist of a fast and a slowly decomposing fraction. This paper describes the results of two different iodometric determination methods, as well as results of dimethylsulfide, acid and nitroxide treatments to determine the difference between the fast and the slowly decomposing fractions. It is concluded that the fast-decomposing peroxides are peracids and that the slowly decomposing peroxides are probably tertiary hydroperoxides.

Thermo-Oxidative Degradation of Polypropylene by Use of Screw Extruders

A homo polypropylene and two polypropylene copolymers with ethylene were thermo-oxidatively degraded by use of screw extruders. They were processed into inflation films and the effect of degree of degradation on the structures and properties of the films were studied.Films processed from degraded polypropylenes show superior transparency and (low temperature) dart impact strength and show inferior openability and slipperiness. Tensile modulus and yield strength are scarcely changed by degradation. This is because films processed from degraded polypropylenes contain more amorphous phase than ones processed from undegraded polypropylenes.

Thermo-Oxidative Degradation of Polypropylene by Use of Screw Extruders

Films were cast from a polypropylene thermo-oxidatively degraded by use of a screw extruder and an undegraded polypropylene with a T-die extruder. The effect of casting conditions on the structures and properties of the films were studied.Films cast from the degraded polypropylene show superior transparency, dart impact strength, and heat sealability and show low stiffness and slipperiness. α-crystal phase is decreased and smectic and amorphous phases are increased by degradation. Although such tendency is also attained by decreasing the chill roll temperature or by increasing die temperature, it is more notable in films cast from the degraded polypropylene than in ones cast from the undegraded polypropylene under any casting conditions. Films cast from the degraded polypropylene have a feature that their inner structures are almost constant independent of the casting conditions.

Evaluation of some commercial copper deactivators by chemiluminescence

The effects of various transition metal stearates (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), some commercial deactivators, and calixarene (cyclic oligomers of a phenol derivative) on the thermo-oxidative degradation of polypropylene were evaluated by the chemiluminescence method and comparison with oxygen uptake results. The time required to observe chemiluminescence was largely dependent on the kind of transition metal added to PP and the relative catalytic order was as follows: Co > Cr > Mn > Fe > Cu > Ni > V > Zn > Ti ⪢ pure. On addition of the copper deactivators, the time required to observe chemiluminescence was delayed and the inhibiting order was as follows: Mark CDA-1 > Chel-180 > OABH > Mark CDA-6. The order determined by the chemiluminescence method coincided fairly closely with those observed by the oxygen uptake method. Calixarene provides not only a copper deactivating function but also an antioxidizing one which was inferior to that of BHT.

Analytical, occupational and toxicologic aspects of the degradation products of polypropylene plastics.

Thermooxidative degradation of polypropylene (PP) at close to the industrial processing temperatures was studied with thermogravimetric analysis, infrared spectroscopy, and gas chromatography-mass spectrometry (GC-MS). GC-MS allowed identification of 47 volatile degradation products. Formaldehyde, acetaldehyde, alpha-methylacrolein, acetic acid, and acetone were the major products. Antioxidants markedly slowed down the degradation of polypropylene and the evolution of the degradation products. The relative amounts of the oxidized products were mostly independent of the degradation temperature or the type of antioxidant. Measurements in the plastics industry revealed low airborne concentrations of individual volatile products. The concentration of aerosols, which infrared analysis showed to resemble paraffin fumes, was significant and probably the most important hygienic hazard. The biochemical parameters (the consumption of protecting sulfhydryl groups and the effects on foreign compound metabolism) indicated that the degradation products are biologically reactive, affecting the balance of normal metabolism in exposed animals.