• Title, Summary, Keyword: chain scission

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Thermo-Degradation Kinetics of Polyethylene (폴리에틸렌의 열분해 Kinetics)

  • Cha, Wang Seog
    • Applied Chemistry for Engineering
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    • v.10 no.3
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    • pp.432-437
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    • 1999
  • Pyrolysis of polyethylene was carried out in the stainless steel reactor of internal volume of $10cm^3$. Pyrolysis reactions were performed at temperature $390{\sim}450^{\circ}C$ and the pyrolysis products were collected separately as reaction products and gas products. The molecular weight distributions(MWDs) of each product were determined by HPLC-GPC and GC analysis. Distribution balance equation for MWDs of random and specific products were proposed to account for initiation-termination and propagation-depropagation, such as hydrogen abstraction, chain cleavage, coupling of polymer and radical. A separate chain-end scission process produces low molecular weight noncondensable gases(C1 through C5) of average molecular weight 38. Activation energies of the random-chain scission and chain-end scission rate parameters, respectively, were determined to be 35, 17 kcal/mole.

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Degradation Characteristics of Perfluoropolyether Lubricant for Computer Hard Disk (컴퓨터 하드디스크 윤활제로 사용되는 Perfluoropolyether의 분해거동)

  • Lee, Ji-Hye;Chun, Sang-Wook;Kang, Ho-Jong
    • Polymer(Korea)
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    • v.31 no.4
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    • pp.278-282
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    • 2007
  • The degradation characteristics of perfluoropolyether (PFPE) for computer hard disk drive have been investigated. Thermal degradation in PFPE started at $170\;^{\circ}C$ and it was completed at $450\;^{\circ}C$. If PFPE was contacted with wear fragment from slider made by $Al_2O_3{\cdot}TiC$, the thermal degradation was accelerated by the catalytic Lewis acid degradation. The Lewis acid degradation mainly took placed in methylene oride(fluoride) chain scission as well as methylene(fluoride) and hydroxy end chain. As a result, the degradation reaction accomplished as early as at $300\;^{\circ}C$. The photo oxidation due to UV exposure on PFPE caused the chain scission in methylene(fluoride), and end chain in PFPE without chain scission in methylene oxide(fluoride) and then the molecular weight of PFPE increased by expected secondary reactions between formed radicals in the photo oxidation.

Comparison of Effects of Ultraviolet and $^{60}$ Co Gamma Ray Irradiation on Nylon 6 Mono-filaments

  • Ohtsuka, Mika;Suzuki, Yoshino;Sakai, Tetsuya;Netravali, Anil N.
    • Fibers and Polymers
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    • v.5 no.3
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    • pp.225-229
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    • 2004
  • The effect of UV and $^60{Co}$ gamma radiations on the physical and mechanical properties of nylon 6 mono-filaments with different draw ratios has been studied. Specimens were exposed to either up to 25 Mrad of gamma or up to 168 hrs of intense UV irradiation. The results show that nylon mono-filaments exposed to gamma rays, with much higher quantum energy than UV, undergo a larger extent of molecular chain scission. Higher irradiation dose also results in the production of insoluble, macroscopic three-dimensional cross-linked network structure. The amorphous regions with a lower density of cohesive energy (lower molecular orientation) show a higher extent of cross linking reaction whereas amorphous regions with a higher density of cohesive energy (higher orientation) show higher extent of chain scission reaction, irrespective of UV ray or gamma ray irradiation.

Characterization of the UV Oxidation of Raw Natural Rubber Thin Film Using Image and FT-IR Analysis

  • Kim, Ik-Sik;Lee, Bok-Won;Sohn, Kyung-Suk;Yoon, Joohoe;Lee, Jung-Hun
    • Elastomers and Composites
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    • v.51 no.1
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    • pp.1-9
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    • 2016
  • Characterization of the UV oxidation for raw natural rubber (NR) was investigated in controlled conditions through image and FT-IR analysis. The UV oxidation was performed on a thin film of natural rubber coated on a KBr window at 254 nm and room temperature to exclude the thermal oxidation. Before or after exposure to UV light, image of the NR thin film was observed at a right or tilted angle. FT-IR absorption spectra were measured in transmission mode with the UV irradiation time. The UV oxidation of NR was examined by the changes of absorption peaks at 3425, 1717, 1084, 1477, 1377, and $833cm^{-1}$ which were assigned to hydroxyl group (-OH), carbonyl group (-C=O), carbon-oxygen bond (-C-O), methylene group $(-CH_2-)$, methyl group $(-CH_3)$, and cis-methine group $(cis-CCH_3=CH-)$, respectively. During the initial exposure period, the results indicated that the appearance of carbonyl group was directly related to the reduction of cis-methine group containing carbon-carbon double bond (-C=C-). Most of aldehydes or ketones from carbon-carbon double bonds were formed very fast by chain scission. A lot of long wide cracks with one orientation at regular intervals which resulted in consecutive chain scission were observed by image analysis. During all exposure periods, on the other hand, it was considered that the continuous increment of hydroxyl and carbonyl group was closely related to the decrement of methylene and methyl group in the allylic position. Therefore, two possible mechanisms for the UV oxidation of NR were suggested.

Characterization on the Ozone Oxidation of Raw Natural Rubber Thin Film using Image and FT-IR Analysis

  • Kim, Ik-Sik;Lee, DooYoul;Sohn, Kyung-Suk;Lee, Jung-Hun;Bae, JoongWoo
    • Elastomers and Composites
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    • v.54 no.2
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    • pp.110-117
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    • 2019
  • The characterization of the ozone oxidation for raw natural rubber (NR) was investigated under controlled conditions through image and fourier transform infrared (FT-IR) analysis. The ozone oxidation was performed on a transparent thin film of raw NR coated on a KBr window in a dark chamber at $40^{\circ}C$ under low humidity conditions to completely exclude thermal, moisture, or light oxidation. The ozone concentration was set at 40 parts per hundred million (pphm). Before or after exposure to ozone, the image of the thin film for raw NR was observed at a right or tilted angle. FT-IR absorption spectra were measured in the transmission mode according to ozone exposure time. The ozone oxidation of NR was determined by the changes in the absorption peaks at 1736, 1715, 1697, and $833cm^{-1}$, which were assigned to an aldehyde group (-CHO), a ketone group (-COR), an inter-hydrogen bond between carbonyl group (-C=O) from an aldehyde or a ketone and an amide group (-CONH-) of protein, and a cis-methine group ($is-CCH_3=CH-$, respectively. During ozone exposure period, the results indicated that the formation of the carbonyl group of aldehyde or ketone was directly related to the decrement of the double bond of cis-1,4-polyisoprene. Only carbonyl compounds such as aldehydes or ketones seemed to be formed through chain scission by ozone. Long thin cracks with one orientation at regular intervals, which resulted in consecutive chain scission, were observed by image analysis. Therefore, one possible two-step mechanism for the formation of aldehyde and ketone was suggested.

Chemical Modification of Isotactic Polypropylene by Melt Blending

  • Kim, Jun-Young;Seo, Eun-Su;Park, Dae-Soon;Park, Kwang-Min;Kang, Seong-Wook;Lee, Chang-Hyung;Kim, Seong-Hum
    • Fibers and Polymers
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    • v.4 no.3
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    • pp.107-113
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    • 2003
  • The branched polypropylene (b-PP) was prepared by melt blending process with initiator, antioxidant, and functional monomers to improve the melt strength through the melt grafting. The melt flow index (MFI) of the b-PP was increased with increasing the initiator content. On the introduction of the alkylamine as the branching agents the MFI of the b-PP was increased, while that of the b-PP with the pentaerythritol triacrylate (PT) was decreased. It may be caused by the chain scission of the i-PP backbone due to the reduced thermal stability of the i-PP on the melt blending. The MFI of the b-PP without the antioxidant was increased due to the chain scission occurred during the melt processing, while on the introduction of the antioxidant, the MFI of the b-PP was decreased. The crystallization temperature of the b-PP was higher than that of PP, which was attributed to the branched chain structure. It was found that the PT was the most effective functional monomers for enhancing the melt properties of the b-PP.

Pyrolysis of PE plastics in the batch type microreactor (회분식 미분반응기를 이용한 PE계 플라스틱의 열분해특성 연구)

  • Kim, Sang-Hoon;Jang, Hyun-Tae;Cha, Wang-Seog
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.8 no.3
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    • pp.632-638
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    • 2007
  • Pyrolysis experiments of HDPE and LDPE were carried out in the stainless steel reactor of internal volume of 40 $cm^3$. Pyrolysis reactions were performed at temperature $410{\sim}460^{\circ}C$ and the pyrolysis products were collected separately as liquid and gas products. The molecular weight distributions(MWDs) and composition of each product were determined by HPLC-GPC and GC analysis. It was represented that the yield and the molecular weight of liquid product were decreased with the increase of reaction temperature and time. The chain-end scission rate parameters, respectively, were determined to be 63.0kcal/mole of HDPE, 45.7kcal/mole of LDPE by the Arrhenius plot.

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Study of UV aging on the performance characteristics of vegetable oil and palm oil derived isocyanate based polyurethane

  • Das, Sonalee;Pandey, Priyanka;Mohanty, Smita;Nayak, Sanjay Kumar
    • Korean Journal of Chemical Engineering
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    • v.34 no.2
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    • pp.523-538
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    • 2017
  • The impact of UV aging on the characteristic properties of synthesized polyurethane (PUs) from castor oil and transesterified castor oil with palm oil based isocyanate and 1,4 butanediol was investigated at different exposure time of 0, 250, 500, 750 and 1,000 h, respectively. The aging properties of the PU films were analyzed through differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) and Tensile tests. The PU films derived from castor oil showed noticeable changes in chemical structure after 250 h of UV exposure owing to chain scission of the urethane group. A considerable decrease in the thermal and tensile properties of the developed PU films was observed due to the plasticization phenomenon. SEM micrographs revealed morphological changes through the appearance of cracks and blisters composed of primary amines on the surface of exposed PU films. However, PUs derived from transesterified castor oil with a higher hydroxyl value exhibited improved UV resistance characteristics due to higher crosslinking and degrade only after 750 h of exposure. Thus, the synthesized green PUs based on transesterified castor oil with palm oil based isocyanate compositions can be candidate materials for developing UV resistant coating material.

The Evaluation of the thermal degradation and the degree of cure of glass/epoxy composite by ultrasonic technique (복합재료의 열화도 및 경화도에 따른 초음파 특성 연구)

  • 강길호;최원종;박상윤
    • Composites Research
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    • v.16 no.6
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    • pp.33-40
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    • 2003
  • The initial thermal degradation of polymer matrix composite is not observed easily. At the beginning of thermal degradation of polymer matrix composites, phase transformation such as chain scission, oxidation occur, and then micro delamination is produced in matrix and interface between matrix and fiber before blistering. Initial heat damage deteriorate mechanical properties of composites. We presented the detection method of the initial heat damage of composites conveniently using ultrasonic technique. Absorption coefficient and material velocity was measured with thermal degradation and degree of cure. The more thermal degradation was progressed, the more absorption coefficient was increased. When the cure temperature is more high, the absorption coefficient of cured composite is increased and material velocity is decreased. We concluded that cure temperature is more high, the defects such as void is increased and molecular structure cured at high temperature has cross-linking structure which is more absorb the ultrasonic waves.

Kinetics of the Low-temperature Pyrolysis of Mixed Plastics in the Batch Reactor (회분식반응기에서의 혼합 플라스틱의 저온열분해 kinetics)

  • Cha, Wang Seog;Oh, Myung Seog;Jang, Hyun Tae;Tae, Beomseok
    • Korean Chemical Engineering Research
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    • v.46 no.3
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    • pp.540-544
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    • 2008
  • Pyrolytic characteristics of mixed plastics containing 22 wt.% HDPE, 17 wt.% LDPE, 27 wt.% PP, 12 wt.% PS, 16 wt.% ABS, 6 wt.% PVC have been studied in the batch-type microreactor of stainless steel. Thermal degradation experiments were performed at temperature of $410{\sim}450^{\circ}C$. The yield of each pyrolytic products were obtained by the weight measurement and molecular weight distribution of pyrolytic liquid products determined by the GC-SIMDIS method. It was shown that the yield and molecular weight of pyrolytic liquid product were decreased with the increase of reaction temperature and time. It was know that 20wt% of PVC composing of the mixed plastics was converted to the gas products of chloride during the pyrolysis process. The chain-end scission rate parameter was determined to be 50.2 kcal/mole of mixed plastics by the Arrhenius plot.