Factors influencing the thermal oxidation of polyethylene

The thermal stability of polyethylene containing conventional antioxidants is adversely affected by contact with copper, by certain pigments, and by the addition of a few percent of polypropylene as a processing aid. Polyethylene inhibited with 0.1% of phenolic antioxidants has approximately the same oxidative stability when in contact with a copper surface as the unprotected polymer. A mechanism is suggested to account for the loss of stability in the presence of copper. Pigments vary in the extent to which they adversely affect the oxidative stability of polyethylene. Since several factors may combine to decrease the stability of protected polyethylene compositions, as determined by accelerated tests, it is essential that their contribution under service conditions be determined. The predicted life at temperatures encountered in service is determined by extrapolating accelerated test data to that constant temperature which is calculated to cause the same degree of degradation as would occur during the daily and seasonal temperature cycles encountered in use.     

Effect of phosphorus-nitrogen-containing fire retardants on thermal decomposition of polyethylene terephthalate

It was found that T-2 fireproofing compound, a mixture of methylphosphonic acid diamide ammonium salt and ammonium chloride, added to PETP alters the direction of the chemical processes in the basic stage of thermal decomposition of the polymer and increases the oxidative stability of carbonized residues, which decreases the inflammability of PETP. The oxygen index of protected PETP is 27–29% with a 5–7% concentration of T-2 fireproofing compound.Moscow State Textile Academy. Translated from Khimicheskie Volokna, No. 1, pp. 31–33, January–February, 1994.     

Graphene/polyethylene terephthalate nanocomposites with enhanced mechanical and thermal properties

Nanocomposites made of poly(ethylene terephthalate) (PET) and graphene nanoplatelets (GNPs) were fabricated through micro-compounding and micro-injection molding. With an objective of improving the interactions between GNP sheets and PET chains, PET pellets were ground into a fine powder. PET pellets and powders were mixed with GNPs at 2%, 5%, 7.5%, and 10% (wt.%), molded to fabricate the nanocomposites, and then tested using several analytical characterization tools. Mechanical testing showed greater improvement through powder mixing, resulting in a 58% increase in the elastic modulus of the nanocomposites at 10% weight fraction. Thermal behavior of the nanocomposites was evaluated through differential scanning calorimetry (DSC), and it was observed that addition of GNPs into PET powders at 10% increased the crystallinity of the PET 50%. Confocal microscopy confirmed that mixing GNP with PET powders results in a more uniform distribution of the GNPs in the matrix compared to the mixture with PET pellets. X-ray diffraction (XRD) analysis confirmed the presence of GNPs with preferred orientation within the PET matrix.

Open image in new window

Graphical abstract GNP distribution analysis in melt-compounded PET nanocomposites

     

Utilization of polyethylene terephthalate waste as a carbon filler in polypropylene matrix: Investigation of mechanical,rheological, and thermal properties

Polyethylene terephthalate (PET) waste was converted into carbon and the feasibility of utilizing it as a reinforcing filler material in a polypropylene (PP) matrix was investigated. The carbon produced by the pyrolysis of waste PET at 900°C in nitrogen atmosphere contains high carbon content (>70 wt%). PP/carbon composites were produced by melt blending process at varying loading concentrations. Scanning electron microscopy images at the fractured surface revealed that the carbon filler has better compatibility with the PP matrix. The mechanical, thermal, and rheological properties and surface morphology of the prepared composites were studied. The thermogravimetric analysis studies showed that the thermal stability of the PP/carbon composites was enhanced from 300 to 370°C with 20 wt% of carbon. At lower angular frequency (0.01 rad/s), the storage modulus (G′) of PP was 0.27 Pa and those of PP with 10 and 20 wt% carbon was 4.06 and 7.25 Pa, respectively. Among the PP/carbon composite prepared, PP with 5 wt% carbon showed the highest tensile strength of 38 MPa, greater than that of neat PP (35 MPa). The tensile modulus was enhanced from 0.9 to 1.2 GPa when the carbon content was increased from 0 to 20 wt%.     

Identification of volatile compounds resulting from the thermal oxidation of polyethylene

The migration of compounds from polymer-based packaging may impart undesirable odors to foods. We, therefore, undertook a study of the volatile compounds produced during the heating of polyethylene (PE) in the presence of excess O₂ at temperatures of 150–350°C and for heating times of 5–15 min. Eightyfour volatile compounds in the range of C₅—C₂₃ were identified by gas chromatography mass spectrometry. The major products were aliphatic hydrocarbons, aldehydes, ketones, and olefins. Changes in temperature and heating times affected the amount and type of compounds produced, with hexanal being found in the largest amount and 300°C resulting in the greatest quantity of volatile compounds. At 350°C, greater amounts and numbers of low-boiling and fewer high-boiling compounds were formed. Only small amounts of volatiles were produced at 150°C. Many of the compounds identified have been reported to have odor and/or toxicological significance. © 1993 John Wiley & Sons, Inc.     

Thermal oxidation of polyethylene terephthalate — acrylic acid copolymers and ionomers

A graft copolymer of polyethylene terephthalate with acrylic acid has been prepared by γ-irradiation. Thermal analysis in air and nitrogen has been made on the original polymer, the acidic copolymer and also on the sodium, lead and cupric salts of the copolymer. In addition to thermal degradation, all samples suffer thermo-oxidative degradation in air in the region of the melting point. The weight loss in air and in nitrogen for all the copolymers at this temperature exceeds that of the ungrafted polymer.     

利用废聚酯合成对苯二甲酸二(2-乙基)己酯

研究了以废聚酯(PET)为原料,钛酸四正丁酯(TBT)为催化剂,在非质子极性溶剂N-甲基-2-吡咯烷酮(NMP)中制备对苯二甲酸二(2-乙基)己酯(DOTP).探索了反应时间、物料摩尔比、溶剂种类和用量对醇解产物收率的影响.结果表明,反应初始阶段为非均相阶段,固-液间传质系数是影响反应速率的主要因素,加入NMP可以加速PET的溶解,促使醇解反应快速进入均相阶段.在n(2-EH)/n (PET)=4,m(TBT)/m (PET)=0.5%,V(2-EH)/V (NMP)=4的条件下,反应2 h,产物DOTP的收率为78.10%.     

纳米SiO2粒子对PET结晶过程的影响

研究了纳米SiO2粒子对PET结晶过程的影响。通过差热分析(DSC),分别研究了改性纳米SiO2对PET的等温结晶和非等温结晶的影响。计算了在不同温度下,不同改性纳米SiO2含量PET的等温结晶动力学方程。结果表明:随着纳米SiO2的加入,可以显著提高PET的结晶性能,Avrami指数n变小,体系发生异相成核。当纳米SiO2的添加量在2％时,体系的结晶能力最好,在所测的5个等温结晶温度中,所有样品在170℃附近的结晶速度最快。