• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.7 s.262
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• pp.732-738
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• 2007

Effects of melt-mixing conditions on fracture properties of hydroxyapatite filled bioabsorbable poly(L-lactic acid)(HA/PLLA) composites was investigated by measuring the firacture toughness value of HA/PLLA composites prepared under different mixing time and rotor speed. The fracture surface morphology was also examined by profile measurement and scanning electron microscopies. It was found that the fracture toughness of HA/PLLA composites decreases due to decrease of ductile deformation of PLLA matrix and debonding of interfaces with increase of the rotor speed and mixing time. Effect of mixing process on neat PLLA was also assessed, and it was found that the fracture toughness of PLLA decreases due to disappearance of multiple craze formation and increase of defects. Such thermal and shear-stress degradation were found to be the primary mechanisms of the degradation of HA/PLLA composites during melt-mixing process.

• The Korean Journal of Rheology
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• v.11 no.1
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• pp.44-49
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• 1999

Effects of particulate size and frictional characteristics were examined on the melting behavior of PP (polypropylene) in a batch mixer. Powder and pellet types of PP were used and each component was blended with PE (polyethylene) wax and clay, respectively. It was observed that small size particulates, i.e. powder systems exhibit accelerated melting behavior; and it was also found that the abrasive additive acts as an effective agent for fast melting of PP powder. Retardation of melting due to the reduced friction was observed in PP pellet/PE wax blends, while melting rate of PP powder was increased by addition of PE wax.

• Polymer(Korea)
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• v.24 no.3
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• pp.374-381
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• 2000

Composites of polypropylene (PP) and organically modified montmorillonite (org-MMT) were prepared by melt mixing in an intensive mixer. Three grades of PP's having different melt viscosities were employed to investigate the dispersion characteristics of the composites with various org-MMT's. Depending on the matrix viscosity and nature of the interlayer in org-MMT significant variations of the phase structure were found. Under the constant mixing condition and matrix viscosity, intercalation of PP chains into the interlayer of org-MMT was possible when initial interlayer distance and packing density were maintained in the optimum range; by which the loss in entropy associated with the confinement of polymer chains was compensated. The state of org-MMT particle dispersion was improved by increasing the matrix viscosity only in the case that dispersed phase is suitable for intercalation process thermodynamically, otherwise little variation was occurred regardless of the matrix viscosity. Due to the lack of specific interaction between PP and erg-MMT considered here, although the intercalation was possible for an appropriate org-MMT, the composites revealed unstable phase structure upon increasing the mixing time, which was characterized by agglomeration of the org-MMT domains.

• The Korean Journal of Rheology
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• v.2 no.2
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• pp.56-65
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• 1990

열방성 액정고분자와 폴리카보네이트를 대상 수지로 하여 용융혼합기로 액정고분자 의 함량, 혼합속도 및 온도등의 변환에 따른 훈련 특성을 측정하고 고분자 혼합물의 혼련조 건과 유변학적 특성 모폴로지 사이의 관계를 조사하였다. 혼련 토크는 100rpm의 혼합속도 에서 극소값을 보이며 혼합기 내의 전단속도가 낮기 때문에 혼력에의해서는 LCP가 섬유상 으로 형성되지 못하고 구형의 입자로 존재함을 알수 있었다. 혼합물의 점도는 시험된 전단 속도 영역에서 순수한 고분자보다 현저히 낮으며 5wt%의 소량 첨가로도 5배의 점도 감소 효과를 보이고 LCP함량이 약 30wt%일 경우 점도 및 혼합에너지가 최소로 되었다. Capillary 레오미터의 실험결과 LCP/PC의 점도비가 1보다 작거나 같튼 전단장하에서 LCP 는 섬유상을 형성하였으며 높은 점도비의 경우 LCP의 변형이 어려워 구형의 입자로 존재하 였다. 또한 혼합물의 PC Tg 이동은 에스터르 교환 반응에 의한 부분적인 혼화성의 증가에 기인함을 알수 있었다.

• Polymer(Korea)
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• v.38 no.2
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• pp.225-231
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• 2014

The rheological properties of highly concentrated polymer bonded explosive simulant were studied by using poly(ethylene-co-vinyl acetate) with 30 and 60% vinyl acetate (VA) content as a binder, respectively. Calcium carbonate and Dechlorane, whose physical properties are similar to resarch department explosive (RDX)'s, were used as fillers. The suspensions were mixed in a batch melt mixer and it was possible to fill 75 v% at maximum. From dynamic mechanical analysis, Dechlorane showed higher interaction with binder resins than that with calcium carbonate fillers. The effects of microstructural change on the rheological properties of the suspensions were investigated by a plate-plate rheometer with constant shear rate and constant shear stress modes, respectively. The theoretical maximum packing fraction of EVA31/Dechlorane suspension obtained from Krieger-Dougherty equation was 70 v% and it was thought that 2000 Pa was proper shear stress condition for this melt processing.

• The Korean Journal of Rheology
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• v.10 no.4
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• pp.247-255
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• 1998

The morphological changes during melt compounding of ternary blends containing various combinations of acrylonitrile-butadiene-styrene(ABS), methyl methacrylate-butadiene-ethyl acrylate(MBE), styrene-acrylonitrile(SAM) copolymers, and poly(methyl methacrylate)(PMMA) as dispersed components in a fixed matrix of polycarbonate(PC) have been investigated. Depending on the composition of the blend, MBE particles and PMMA phase appear to locate at the PC-SAN interface under the influence of interfacial tensions and motion induced coalescence. The interfacial viscosity is found to be a critical factor that affects the amount of coalescence.

• Journal of Adhesion and Interface
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• v.15 no.4
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• pp.169-173
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• 2014

The effect of filler sizes on the thermal diffusivity of Nylon 66/SiC composites was investigated. By loading 60 vol% of SiC fillers on Nylon 66, the thermal diffusivity of the composites increased more than 10 times than that of unfilled Nylon 66 and the thermal diffusivity of composites with filler sizes of $24{\mu}m$ and $76{\mu}m$ increased to $2.2{\times}10^{-2}cm^2/sec$ and $1.75{\times}10^{-2}cm^2/sec$, respectively. It is speculated that the smaller filler size ($24{\mu}m$) of SiC is more favorable for the formation of thermal conductive path that the larger size ($76{\mu}m$) of filler composites. The thermal diffusivity of Nylon 46/SiC 400 (60 vol%) composites was $1.61{\times}10^{-2}cm^2/sec$ that was lower than that of Nylon 66/SiC (60 vol%) composites.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.305-315
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• 2021

An intermeshing corotating twin screw extruder is mainly used for compounding polymeric materials. Twin screw extruder can adopt modular-type screw configurations, which directly controls the quality and productivity of the products. The types, shapes, and specifications of the screw and kneading elements are summarized, and the effects of screw configuration on the processabiliy of the materials are discussed. The principles of screw configuration universally applied to mass production of general-purpose resins are explained, and the guidelines of screw combination according to the roles of feeding, melt mixing, and metering zones are listed. The strategies of screw combination suitable for various cases, such as side feeding of liquid additives or inorganic fillers, reactive extrusion, devolatilization process, production of products requiring bright color and transparency, and processing of materials with low apparent specific gravity, are presented.

• Polymer(Korea)
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• v.24 no.3
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• pp.366-373
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• 2000

In this study, the PPS/ABS blend system was investigated in order to collectively identify the relationship among blend morphology, chemical compatibilization and thermal property. ABS resin was chemically modified by the incorporation of maleic anhydride through reactive extrusion for enhanced compatibilization, and PPS, ABS and the modified ABS were blend by a sing twin screw extruder. The effect of chemical modification of ABS on the morphological, mechanical, and thermal properities of the resulting blend was examined. A strong interaction was observed between PPS and MABS by optical microsopy as well as scanning electron microscopy, exhibiting a well-dispersed morphological feature. The PPS/MABS blend showing a single glass transition temperature was observed in dynamic mechanical analysis, demonstrating a pseudo-homogeneous phase morphology induced by chemical compatibilization. PPS/MABS blend also exhibited an enhanced thermal stability and heat distortion temperature compared with modified PPS/ABS blend.

• Polymer(Korea)
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• v.38 no.4
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• pp.417-424
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• 2014

Reactivity and rheological behavior of highly concentrated polymer bonded explosives (PBX) simulant was studied. As a binder, thermosetting hydroxyl terminated polybutadiene (HTPB) was used. By using bimodal $CaCO_3$ (size ratio 10:1) and sugar particles (size ratio 25:1) as fillers, maximum 75 v% filling was possible during melt mixing. The relative viscosities of bimodal suspension were much lower than those of unimodal one and showed minimum values at 0.25 of fine particle fraction. In curing experiment, as curing temperature increased, the time of initiation and completeness of curing reaction became shortened, the torque kept low, and the change of internal temperature decreased.