• Applied Chemistry for Engineering
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• v.8 no.5
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• pp.837-843
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• 1997

In oxidized polyethylene wax preparation, the effects of main parameters such as the property of used wax, oxidation time, oxidation temperature, air feed rates on the change of acid-numbers were investigated. The change in polymer property was also investigated. The results showed under given reaction conditions, the acid numbers with oxidation temperature increased upto $160^{\circ}C$, but at higher temperature, it decreased. The base resin which was lower molecular weight had higher acid number. The result showed molecular weight as a experimental parameter was more effective than density in oxidation experiment. In milder condition, free radical initiator was used for catalyst to get higher acid-numbers, which was successful in comparison to the non-catalyst system. Also the catalyst with longer half-life was efficient, in order of DCPO, HOPO and BPO.

• Journal of the Korea Organic Resources Recycling Association
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• v.6 no.1
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• pp.1-12
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• 1998

To examine the possibility of protein recycling of shaving scraps containing chromium generated from manufacturing process of leather, the optimum hydrolysis conditions and the withdrawal methods of low molecular weight protein for using the liquid fertilizer sources by investigation of solubilities of hydrolyzed protein, inorganic nutrients contents and molecular weight distributions of hydrolyzed protein from shaving scraps treated with mixed alkaline inducing agents and mixed alkaline proteolytic enzymes including MgO were investigated. In hydrolysis of shaving scraps treated with mixed alkaline inducing agents, the solubility of shaving scraps were clearly different with 65~85% according to the sorts of the inducing agents, and the degree of hydrolysis was high in the order of NaOH, $Ca(OH)_2$ and KOH. The average molecular weights of withdrawal hydrolyzed protein were 10, 40 and 80 KD treated with NaOH, $Ca(OH)_2$ and KOH, respectively. And the chromium contents was about 15 ppm. In hydrolysis of shaving scraps treated with mixed alkaline proteolytic enzymes, the bility of shaving scraps were high in the order of alcalase, esperase and savinase. In c of treating 0.5% alcalase, the low molecular weight of hydrolyzed protein could be withdrawn. The solubility of the hydrolyzed protein was about 85%, the average molecular weight of the protein was below 1 KD and chrome content of the protein was below 10 ppm.

• 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.

• Applied Chemistry for Engineering
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• v.10 no.1
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• pp.35-40
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• 1999

The variations of the glass transition, melting peaks, molecular weight and its distribution (polydispersity index: PI) due to the annealing temperature and time have been investigated using the thermoplastic segmented polyurethanes (TPUs) and its blends based on the contents of hard segment. The position of the melting peak and its magnitude have been increased with the annealing temperature and time. This may be arised from the rearrangement of the microdomain structure due to the long-range or short-range segmental motion, the order-disorder transition of non-crystalline microphase, the variation of the domain size or the degree of disorder of crystalline structure by given different thermal histories. The annealing temperature and time affected the molecular weights and polydispersity : the number and weight average molecular weights were increased, while the polydispersity index (PI) deceased at certain temperatures : for TPU-35 at $135^{\circ}C$, for TPU-44 at $170^{\circ}C$ and for TPU-53 at $180^{\circ}C$. The temperatures which give the variations in molecular weights and in PIs are consistent with the annealing temperatures of which $T_3$ solely exists for each sample. Thus it is suggested that the chain dissosiation and recombination simultaneously occur at the above mentioned temperature for each sample.

• Elastomers and Composites
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• v.44 no.2
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• pp.156-163
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• 2009

Our objective is to increase the flowability of Polypropylene(PP) compounds and achieve flow mark free surface in injection molded specimen. We have investigated flowabilities of PP compounds which were composed of PP, rubber, talc, and trace amount of additives. Flowability measurement was performed with four types PPs of which molecular weight distributions(MWD) and melt indexes(MI) were different. Rheological properties of the PP compounding materials, such as spiral flow(SF) length, MI, and shear viscosity, were evaluated. When PP with the broad MWD was used, there were remarkable cases where the spiral flow length of low MI PP compound was longer than that of higher MI PP compound. The PP compound having low MI but broad MWD PP has more flowability than the compound with only high MI.

• Composites Research
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• v.32 no.3
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• pp.163-169
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• 2019

In this paper, we constructed a molecular dynamics (MD) polymer model of PMMA with 95% of conversion by using dynamic polymerization algorithm of a thermoplastic polymer based on free radical polymerization. In this algorithm, we introduced a united-atom level coarse-grained force field that combines the non-bonded terms from the TraPPE-UA force field and the bonded terms from the PCFF force field to alleviate the computation efforts. The molecular weight distribution and the average molecular weight of the polymer were calculated by investigating each chain generated from the free radical polymerization simulation. The molecular weight of the polymer was controlled by the number of initiator radicals presented in the initial state and molecular weight effect to the density, the glass transition temperature, and the mechanical properties were studied.

• Analytical Science and Technology
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• v.16 no.4
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• pp.292-298
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• 2003

In this study, the photooxidation and ozonation of humic acid (HA) in aqueous solution were conducted and the treated HA samples at different reaction time were analyzed using ultrafiltration techniques to evaluate the change of their molecular size distributions with its DOC removal. Molecular size distribution of untreated HA showed 41.5% in higher molecular size fractions (>30,000 daltons) and 15.2% in much smaller molecular size fraction (<500 daltons). As UV irradiation time was increased, it was observed that the degradation of the large molecules of the fraction of >30,000 daltons into much smaller molecules was increased. In UV system, the HA molecules of the fraction of <500 daltons became significantly more and its percentage was increased from 35.3% (UV only irradiation) to 58.9% ($UV/TiO_2$) and 87.8% ($UV/H_2O_2$) in the presence of the photocatalysis. Otherwise, ozonation of HA produced mainly the fraction of medium molecular size ranging from 3,000 to 30,000 daltons with much lower portion (<~7%) in the fraction of <500 daltons. In ozone only system, the fraction of 30,000~10,000 daltons occupied in 41.5% at 60 min of ozonation time. In $O_3/H_2O_2$ system, the fraction of 30,000~10,000 daltons and 10,000~3,000 daltons occupied in 38.9% and 36.2% respectively. Based on these results, we suggested applicable treatment process which could be combined with $UV/H_2O_2$, $UV/TiO_2$ and $O_3$, $O_3/H_2O_2$ system for more effective removal of humic acid in water treatment.

• The tire
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• s.61
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• pp.16-19
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• 1975

무우니이점도 30에서 70까지의 천연고무(이하 NR이라고 약)와 합성 시스-1,4-포리이소프렌(이하 IR이라고 약)의 완화탄성률에 대해서 검토했다. 완화탄성률은 -50℃로부터 90℃이며 시간 3초로부터 3,000초에 긍해서 측정했다. 동일한 무우니이점도로서 어느 온도에 있어서도 IR의 완화탄성률은 NR에 비하면 작으며 따라서 IR은 부드럽게 촉감된다고 생각된다. NR과 IR의 각종온도에서의 완화탄성률과 시간의 관계는 같은 환산계수를 사용해서 중합이 가능했었다. 얻어진 합성곡선에 대해서 특히 종단역에 있어서 NR의 완화탄성률이 IR에 비해서 크다. 이것은 같은 무우니이점도로서 NR쪽이 IR에 비하여 높은 평균분자량과 넓은 분자량분포를 가지기 때문이라고 생각된다.

• Applied Chemistry for Engineering
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• v.10 no.1
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• pp.19-23
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• 1999

Chitosan was partially degraded by using nitrous acid. The deacetylation degree of chitosan decreased with its degree of hydrolysis. Deacetylation degree of each fraction was less than 50%. The degraded product was fractionated by means of precipitation using aqueous methanol solution or aqueous methanol-acetone solution. The molecular weight of each fraction was distributed between 6000 and 4000, and below 2000 for being precipitated using aqueous methanol solution and aqueous methanol-acetone solution respectively. They had narrow molecular weight distributions, and their polydispersities were less than 1.7. The antibacterial activities for each fraction were evaluated against Bacillus subtilis HB 101 and E. coli PP 2, gram-positive bacteria and gram-negative bacteria, respectively. Fraction B (Mw=5100) showed high antibacteiral activity. All fractions were more active against Bacillus subtilis than E. coli.

• Journal of the Korean Applied Science and Technology
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• v.36 no.3
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• pp.1018-1027
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• 2019

Natural-derived protein-derived low molecular weight peptides have been known to have physiological activities such as antioxidant, hypertension relief, immunomodulation, pain relief and antimicrobial activity. In this study, the low-molecular peptides were produced using commercial proteases (alcalase, bromelain, flavourzyme, neutrase, papain, protamex), and the antioxidant activity (DPPH scavenging activity, superoxide radical scavenging activity, hydroxy radical scavenging activity, and metals chelation capacity), constituent amino acid and molecular weight of the peptide were analyzed. Enzyme reaction was performed by adding 50 g of chopped Ogae meat slurry and 2%(w/v) protein enzyme into the enzyme reactor for 2 h at a pH of 6 and a temperature of $60^{\circ}C$. The degree of hydrolysis(%) after the reaction ranged from $36.65{\pm}4.10%$ to $70.75{\pm}5.29%$. The highest degree of hydrolysis of protamex was 46.3%, and the highest value of papain hydrolysate was $70.75{\pm}5.29%$. On the other hand, alcalase hydrolysate showed the lowest value of $36.65{\pm}4.10%$. Bromelain-treated low molecular weight peptides showed the highest DPPH radical scavenging activity and the lowest scavenging activity of alcalase-treated peptides. Superoxide radical scavenging activity showed that bromelain treated low molecular peptide showed the highest radical scavenging activity of 50% or more. Hydroxyl radical scavenging activity ranged from about 16.73 to 69.16%, the highest among bromelain-treated low molecular peptides. $Fe^{2+}$ chelation abilities showed a distribution between about 17.85 to 47.84%. The chelation capacity of the hydrolysates was not significantly different without any difference to the enzymes used. The results of amino acid analysis showed differences between hydrolysates of alcalase, bromelain, flavourzyme, neutrase, papain, and protamex enzymes. The most amino acid was glutamic acid. The molecular weight distribution of the enzyme hydrolyzates was in the range of 300-2,000 Da, although the molecular weight distribution differed according to the treated enzymes.