• Polymer(Korea)
• /
• v.29 no.4
• /
• pp.385-391
• /
• 2005

Reactive melt processing has been carried out to investigate crosslinking characteristics of high density polyethylene OTDPE) with dicummyl peroxide (DCP) and perbutyle peroxide (PBP). The increase of torque in the internal mixer indicated that the crosslinking in HDPE has been occurred by peroxides. As a result, the substantial decrease of density, melting temperature, and melt enthalpy were found while the melt viscosity increased in partially crosslinked HDPE. In the mechanical properties of partially crosslinked HDPE, the increase of maximum strength and the decrease in elongation at break were clearly noticed and these were more pronounced when PBP was applied as a crosslinking agent. It seems that the maximum strength was obtained with reactive processing temperature at $150^{circ}C$, however, the mixing time did not affect to the strength of partially crosslinked HDPE.

• Membrane Journal
• /
• v.14 no.3
• /
• pp.240-249
• /
• 2004

Crosslinked PVA membranes were achieved by esterification between the hydroxyl groups of PVA and carboxyl group of sulfosuccinic acid (SSA). SSA containing sulfonic group was used as a chemical crosslinking agent as well as a donor of fixed anionic group ($-SO_3$H). The crosslinking density of membranes was controlled by SSA content and calculated using polar and non-polar solvent. The crosslinking density measured by using non-polar solvent such as xylene and benzene increases with SSA content. However, using the polar solvent such as water and methanol, the crosslinking density increases up to SSA content of 20 wt% and above the content decrease due to sulfonic acid groups. The crosslinked PVA membranes were studied in relation with water diffusion coefficient and mechanical property as well as proton conductivity and methanol permeability as a function of crosslinking density. These properties were all dependent on the effect of SSA content.

• Elastomers and Composites
• /
• v.40 no.1
• /
• pp.12-21
• /
• 2005

In this work, magnesium carbonate and calcium hydroxide as metallic crosslinking agent were added to chlorosulfonated polyethylene rubber (CSM) emulsion to enhance the mechanical properties of emulsion film such as tensile strength, elongation at break, and tear strength and crosslinking density, thermal features, and surface energy were also investigated. Crosslinking density of the CSM emulsion film with increasing the amount of magnesium carbonate and calcium hydroxide increased, leading to the enhancement of water resistance. It was shown that compared with calcium hydroxide, magnesium carbonate had a little higher crosslinking density and $T_g$ value. The surface energy and mechanical characteristics of the CSM emulsion film, however, showed somewhat different behaviors. The highest surface energy, tensile strength, and tear strength were observed when 0.75% for magnesium carbonate and 1.0% for calcium hydroxide were added respectively. Therefore, it can be concluded that as metallic crosslinking agent to improve water resistance and mechanical properties of the CSM emulsion, magnesium carbonate is more preferable to calcium hydroxide.

• Rubber Technology
• /
• v.11 no.1
• /
• pp.12-26
• /
• 2010

각종 산업제품의 주요 부품으로 사용되고 있는 고무재료는 사용 중 온도변화에 의해 체적 또는 길이 변화를 수반할 수 있어 결과적으로 고무제품의 성능이나 효율이 영향을 받게 된다. 특히 고온에서 고무제품의 치수변화를 제한하거나 일정치수를 강제할 경우 열수축이나 열팽창에 의해 응력이 발생하게 된다. 따라서 온도 변화에 따른 열응력의 측정은 고무제품의 정밀성과 성능을 평가하는 중요한 수단을 제공한다. 본 연구에서는 고무소재의 열응력 측정을 위한 새로운 측정방법을 개발하였고 이와 관련 새로운 시험장치를 설계, 제작하였다. 고무시편에 일정 변형의 인장을 준 상태에서 가열하면 열응력이 발생한다. 이 때의 열응력은 고무분자 사슬들의 운동성에 기인하며 배향된 고무분자 사슬들이 열역학적으로 랜덤 사슬형태로 돌아가려는 엔트로피적 힘이다. 따라서 온도가 높을수록 그 수축력은 증가하게 된다. 또한 고무분자 사슬의 사전 변형이 증가하면 그 열응력은 증가한다. 이때 열응력은 측정시간이 지남에 따라 최대치에 도달한 후 완화되며 그 완화속도는 설정온도에 의해 영향을 받는다. 여기서는 온도변화에 따른 고무시편의 열응력 측정결과를 소개하고, 고무분자 사슬의 엔트로피 변화와 점탄성적 흐름, 그리고 가열에 따른 고무 시편의 팽창 또는 수축이 열응력에 미치는 영향 등을 논의하였다. 특히 천연고무와 SBR 고무시편의 열응력 차이를 분자사슬의 운동과 연관하여 검토하였고, 가교밀도와 가교시스템이 각각 다른 고무시편에 대해 열응력 발생과에 따른 상관관계를 고찰하였다. 또한 시편의 형태와 두께가 열응력 발생에 미치는 영향도 검토하였다. 충전 배합고무의 경우 열응력에 영향을 미치는 인자로 고무분자 사슬의 운동성과 가교밀도 외에 고무재료와 충전제 사이의 물리 화학적 상호작용도 매우 중요한 요소가 된다. 배합고무에서 충전제의 영향을 검토하기 위해 실리카와 카본블랙을 선택하였고 배합고무의 열응력을 각각 측정하여 이들의 보강효과가 열응력에 미치는 영향에 대해 논하였다.

• Polymer(Korea)
• /
• v.36 no.2
• /
• pp.235-244
• /
• 2012

A thiazole type accelerator MBT (2-mercapto benzothiazole) was added into silica filled natural rubber (NR) compound with various concentrations (0, 1, 2, 3, 4 phr). The effects of MBT on the cure rate, mechanical property, degree of rubber-filler interaction (${\alpha}_F$), crosslinking density, and viscoelastic property ($tan{\delta}$) were investigated. As accelerator concentration increased, the $t_{s2}$ and $t_{90}$ decreased and the crosslinking density and modulus at 300% elongation increased. The tensile strength and elongation increased up to 3 phr and no further increased at 4 phr. The $tan{\delta}$ value measured at room temperature was higher than that of the $70^{\circ}C$. The ${\alpha}_F$ value was not affected by the addition of MBT. The mechanisms for the vulcanization rate were reviewed.

• Polymer(Korea)
• /
• v.32 no.1
• /
• pp.1-6
• /
• 2008

The adhesion behaviors and processability of NBR as a sealing material were investigated. In order to find the optimum formulation, the adhesive properties and processability were observed as the change of the contents of acrylonitrile (ACN) in NBR. Effects of Mooney viscosity, filler, plasticizer and crosslinking agent on the adhesion behaviors were also studied. The contents of ACN in NBR have great effects on adhesion behaviors and processability in NBR sealing. To know the optimum condition of roll mixing, degree of dispersion was investigated. It was confirmed that degree of dispersion was influenced by various factors such as mixing order, time, and temperature. The crosslinking system was studied as the observation of sulfur system, peroxide system, crosslinking density, and structure. From the variation of the dry condition and hexamine contents, the relation between adhesive and NBR was studied. These results show the adhesion properties and processability are dependent on the contents of ACN and crosslinking system.

• Corrosion Science and Technology
• /
• v.15 no.6
• /
• pp.297-302
• /
• 2016

Water-based systems are dominating the coating market because of worldwide VOCs regulations. Research is focusing especially on waterborne polyurethane (WPU) because of its unique mechanical and chemical properties. However, commercial WPU consists of linear thermoplastic polymers with polar groups on the main chain, which do not perform as well as solvent-borne PU in a two-pack system. In this study, APTES were used as a chain crosslink agent to overcome commercial WPU's limited performance. WPUs synthesized by using a sol-gel process were evaluated with FT-IR, particle analysis, TGA, tensile tests, pull-off tests, SEM, and EIS. The results showed that WPUs with added APTES had better thermal stability, mechanical properties, and water resistance than did WPUs without added APTES. Consequently, the sol-gel process increased the crosslink density of WPUs and modified the WPU's own properties.

• Elastomers and Composites
• /
• v.47 no.2
• /
• pp.156-161
• /
• 2012

Difference in recovery behaviors from the circular deformation of natural rubber (NR) composites aged in air and distilled water, respectively were investigated. Recoveries of the samples aged in air were larger than those of the samples aged in distilled water. Recovery rates of the samples reinforced with filler were faster than those of the unreinforced ones. Recovery rates of the carbon black-filled samples were faster than those of the silica-filled ones. Difference in the recovery behaviors according to the aging media can be explained by the crosslinking density changes and the annealing effect.

• Journal of the Korean Chemical Society
• /
• v.46 no.3
• /
• pp.233-240
• /
• 2002

In this work, the cure kinetics and rheological and mechanical properties of diglycidylether of bispheonol A (DGEBA, EP)/polyurethane (PU) blends were investigated. The 1 wt% N-benzylpyrazinium hexafluoroantiminate (BPH) was used as a latent thermal catalyst. Latent properties were performed by measurement of the conversion as a function of reaction temperature using DSC. And the rheological properties of the blend systems were investigated under isothermal conditions using a rheometer. Crosslinking activating energies (Ec) were also determined from the Arrhenius equation based on gel time and curing temperature. The impact strengths were measured as mechanical properties of the casting specimens. The BPH in the blend systems could be an excellent latent thermal catalyst without any co-initiator. The rheological results showed that Ec was highest when PU content was 30 wt% which was in good agreement with the impact strengths. This was probably due to the intermolecular hydrogen bonding between the hydroxyl group in PU and EP, resulting in increasing the crosslinking density.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2009.06a
• /
• pp.255-255
• /
• 2009

에폭시수지에 유기화된 층상실리케이트 나노입자를 충진하여 에폭시-나노콤포지트 제조하였다. 에폭시-나노콤포지트는 열적, 기계적 특성이 매우 우수한 콤포지트로서 실란처리에 따른 동적 기계적 특성 (Dynamic Mechanical Analysis)과 가교밀도와의 관계를 조사였다. 나노입자의 충진함량은 3wt%로 충진하였고, Silane Coupling Agent는 에폭시실란으로서 3-Glycidoxypropyltrimethoxysilane이 사용되었다. 실란처리함량은 0.5, 1, 1.5 wt%로서 적용하여 제조된 샘플이다. DMA Storage modulus특성으로 glass state($40^{\circ}C$)에서는 원형에폭시의 경우 2054, 실란처리되지 않은 나노콤포지트 3967, 실란처리된 나노콤포지트는 4867MPa을 나타내었다. rubbery state($140^{\circ}C$)에서는 원형에폭시의 경우 1458, 실란처리되지 않은 경우 2506, 실란처리된 나노콤포지트는 2638MPa을 나타내었다. 또한 실란처리함량에따른 가교밀도변화는 0.5wt%에서는 0.803, 1 wt%에서는 0.671, 1.5wt%에서는 $0.762[mol/cm^3]$이로서 에폭시원형과 실란미처리된 나노콤포지트 그리고 실란처리된 나노콤포지트순으로 glass state와 rubbery state에서의 특성이 크게 향상된 결과를 얻었다. 이는 실란이 고분자와 무기물사이의 결합력을 강화시켜 열적기계적 특성향상을 가져 오는 것으로 볼 수 있다. 가교밀도의 실란처리함량의 변화에 있어서 과량의 함량 첨가는 에폭시와 나노층상실리게이트 표면처리된 잔유량이 오히려 특성의 저하를 가져오는 것으로 볼 수 있다.