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1 Elastomers and Composites Vol. 52, No. 3, pp. 211~215 (September 2017) Print ISSN /Online ISSN DOI: A Study of Characteristics Variation of Thermally Expandable Microspheres in Post-polymerization Treatment by Various Initiators Hae Na You, Ji Hoo Kim, Myeong Woo Kim, Keon Il Kim, and Hyun Duk Park Kum Yang Co., Ltd., 81, Nakdong-daero 960 beon-gil, Sasang-gu, Busan 47028, Korea (Received September 14, 2017, Revised September 20, 2017, Accepted September 26, 2017) Abstract: Thermally expandable microspheres were used as post-treatment initiators of potassium persulfate, sodium bisulfite, and sodium sulfide in order to improve the foaming ability and whiteness when foaming a mixture of thermally expandable microsphers and poly(vinyl chloride). Potassium persulfate showed no significant influence on the foaming behavior, foam expansion, whiteness, and yellowing, whereas in the case of using sodium bisulfite. In particular, sodium bisulfite demonstrated the best efficiency with 2 wt% treatment. The thermally expandable microspheres prepared herein can provide excellent foamability and whiteness, and are expected to be applicable in various fields such as general coating and wallpaper. Keywords: potassium persulfate, sodium bisulfite, thermally expandable microsphere, post-treatment Introduction 열팽창성미소구는액체탄화수소가 3~7 µm 두께의셀에감싸져있는형태의코어-셀구조로약 5~50 µm의평균입도를갖는고분자입자이다. 1 이들열팽창성미소구에포함된팽창제는주로이소부탄이나이소펜탄등의탄화수소가주로사용되는데, 이들은열팽창성미소구외각의고분자연화점 (softening temperature) 보다끓는점이낮으며, 증기압이높아열팽창미소구에열을가하면팽창전에비해부피가 50~100 배로팽창하는특성을가지고있다. 2-4 이러한특성으로인해열팽창성미소구는다양한분야에적용되고있다. 일반적으로질량감소, 벌크증가또는탄력성이개선된경량제품과같은맞춤형재료특성을달성하는데사용된다. 또한, 열팽창성미소구를인쇄잉크에첨가하면벽지, 섬유및점자형인쇄에 3 차원질감을가능하게한다. 1 Acrylonitrile과 methacrylonitrile과같은 nitrile계열의단량체들이기체차단성이우수하기때문에일반적으로열팽창성미소구의핵심단량체로사용된다. 5 하지만고분자중합반응은단량체가 100% 중합체로전환되지않기때문에일부미량의미반응단량체가중합체에잔류하게된다. 6 중합후중합체표면에단량체들이잔류하게되면중합체의물성저하를유도하며, 특히단량체의산화로인하여변색을유발할수도있다. 7 이러한이유로열팽창성미소구를이용하여, 높은백색도를요구하는곳에적용하는데있어서제한적이다. Corresponding author hypark042@kyc.co.kr 이를완화하기위하여중합체에잔류모노머제거를목적으로다양한방법들이제안되고있다. Acrylonitrile copolymer 를합성시에중합온도를증가시켜전환율을향상시키는방법으로잔류 acrylonitrile의함량을감소시킨결과가있었으나, 열팽창성미소구내부에팽창제가존재하기때문에중합온도를상승시키기는어려웠다. 8 또한, 중합체에잔류모노머를제거하기위해 stripping법을사용하였으나, 이또한열팽창성미소구가팽창되어적용하기에는무리가있었다. 9 잔류 acrylonitrile을흡착제를사용하여제거한연구도있었으나, 수중에잔존하는 acrylonitrile의제거는효과적이지만중합체표면에미세하게존재하는 acrylonitrile의제거는효과적으로진행되지못하였다. 10 Post-polymerization 방법으로잔존하는모노머를제거하는연구가일부진행되었으나, 벽지및코팅과같은산업분야에적용하기위하여 poly(vinyl chloride) 등의매질에서동일내지는이상의발포율을유지하면서백색도향상및황변감소로이어지는 post-polymerization의연구는진행되지못하였으며, 이를개선하기위하여개시제의종류나함량에따른 postpolymerization을통해백색도향상및황변을개선시키기위한연구를진행하였다. Experimental 1. 열팽창성미소구의합성열팽창성미소구의합성방법은 Figure 1과같이합성하였

212 Hae Na You et al. / Elastomers and Composites Vol. 52, No. 3, pp. 211-215 (September 2017) sodium bisulfide, sodium sulfite와같은개시제를첨가하고용기를밀폐시키고 5시간동안 70 o C로반응시켰다.

2 212 Hae Na You et al. / Elastomers and Composites Vol. 52, No. 3, pp (September 2017) sodium bisulfide, sodium sulfite와같은개시제를첨가하고용기를밀폐시키고 5시간동안 70 o C로반응시켰다. 반응이끝난후생성물을여과, 건조하여후처리된열팽창성미소구를얻었다. 3. PVC 졸발포시험 Figure 1. Preparation process of thermally expandable microspheres. 다. 먼저수상분산매는이온교환수 (228 g), sodium chloride (72 g, GR grade, Junsei), colloidal silica (15 g, SS-SOL 30A, POC), polyvinylpyrrolidone (1 g, K-30, Samchum Chem.), 10% sodium nitrite 수용액 (0.7 g, GR grade, Samchum Chem.) 을첨가하여조제하였다. 유상혼합물은 acrylonitrile (30 g, EP grade, Junsei), methyl methacrylate (12 g, GR grade, Junsei), trimethylopropane trimethacrylate (0.15 g, technical grade, Sigma-Aldrich), Iso-pentane (16 g, GR grade, Samchum Chem.) Azobisisobutyronitrile (0.5 g, GR grade, Samchum Chem.) 을혼합하여조제하였다. 이후에수상분산매와유상혼합물을혼합하고, 얻어진혼합액을호모믹서에의해 1000 rpm으로 10분간분산시켜현탁액을조제하였다. 이현탁액을용량 1리터가압반응기에서질소치환후, 반응초기압력 0.2 MPa로하여 400 rpm으로교반하면서중합온도 60 o C에서 16 시간중합하였다. 중합이끝난후생성물을여과, 건조하여열팽창성미소구를얻었다. 합성한열팽창성미소구의열팽창특성은열팽창분석기 (TA instrument, TMA Q400) 를사용하여 50 o C에서 250 o C까지 10 o C/min. 의승온속도로가열하면서팽창이개시되는온도 (T start ), 최대팽창에도달된때의온도 (T max ), 최대팽창에도달했을때의높이 (D max ) 를측정하였다. 합성한미소구의표면은전자주사현미경 (Seron, SEM AIS2300C) 과광학현미경 (Nikon, E200LED) 을이용하여촬영을하였다. 또한, 합성한미소구의평균입자사이즈 (D50) 는입도분석기 (Malvern, Mastersizer 2000S) 를이용하여측정하였다. 합성한열팽창성미소구의 poly(vinyl chloride) (PVC) 졸발포시험은 PVC (100 g, LG화학, LP170), 디옥틸프탈레이트 (60 g, Sigma-Aldrich) 중질탄산칼슘 (40 g Sigma-Aldrich), BZ810P-5 (1 g, Songwon) 를혼합하여 PVC 졸을형성한후형성된 PVC 졸에건조된열팽창성미소구 1g을추가로첨가한후블렌드하여혼합물을제조하였다. 이후제조한혼합물을벽지위에 200 µm 두께로코팅하였다. 코팅된시편은 110 o C에서겔화시키고, 겔화된시편을두께측정기로측정하였다. 이후겔화시킨시편을 200 o C에서발포후두께를측정하여팽창전과팽창후의두께를나누어팽창비를계산하였다. 4. 색차계에의한시험편의변색측정 PVC 졸발포시편의명도, 색상및채도를측정하기위해색차계 (Konika Minolta, CM-2500d) 를이용하여 Whiteness index (WI) 값과황변도 (b) 값을측정하였다. Results and Discussion 1. 합성한열팽창성미소구의형상비교 Figure 2(a) 는개시제로처리하기전의미소구를현미경으 2. Post-polymerization 열팽창성미소구를중합시킨후, potassium persulfate, Figure 2. Microscopic images of microcapsules (a) None, (b) Potassium persulfate, (c) bisulfite, and (d) sulfide.

3 A Study of Characteristics Variation of Thermally Expandable Microspheres in Post-polymerization Treatment by Various Initiators 213 로찰영한것이며, (b), (c), (d) 는각각 potassium persulfate, sodium bisulfite, sodium sulfide 개시제를 1wt% 로후처리한미소구이다. Figure 2(b), (c) 는 Figure 2(a) 와비슷한형상을보이나, Figure 2(d) 의경우열팽창성미소구를후처리한후에입자들이서로뭉쳐서열팽창성미소구들사이의간격이굉장히넓게분포되어있는것을확인할수있으며, 이는 sodium sulfide로후처리시, 열팽창성미소구외부붕괴로인해내부의탄화수소가유출되어다른개시제의후처리에비해뭉쳐져있는것으로보여진다. 2. 합성한열팽창성미소구의열팽창특성비교 개시제로후처리한열팽창성미소구의물성결과는 Table 1에서보이는바와같이개시제의사용으로인해, 체적변화가거의발생되지않은 sodium sulfide를제외하고는 T start 는차이가없었고, sodium bisulfite의 T max 가가장높았다. sulfide의 D max 는다른개시제에비해현저히낮은수치를나타내었고, 이는후처리시열팽창성미소구내탄화수소가붕괴된외곽벽으로유출되어발포역할을제대로하지못한것으로보인다. 개시제로후처리한열팽창성미소구의 TMA curve를 Figure 3에나타내었고, 후처리하기전과비교할때, potassium persulfate는체적변화가적었고, sodium bisulfite의경우약간의체적증가를보였다. sulfite의경우체적증가가상대적으로낮았고, 이는후처리과정에서열팽창성미소구외곽고분자의기체차단성을낮게하여내부탄화수소가유출되어체적변화가거의일어나지않은것으로보인다. bisulfite로후처리한경우에는잔류모노머의제거가효과적으로이루어져다른개시제로후처리한경우와비교시, 단위질량당열팽창성미소구자체함량이높아져체적변화가가장큰것으로보인다. Figure 4는합성한열팽창성미소구에대해, SEM을이용하여촬영한결과이다. 합성한열팽창성미소구는형태가다소일그러진구형의형태를가지는것을볼수있다. 이는합성시가교제에의해서캡슐형상이구형에서점차적으로일그러진형태의미소구로변형된다고보고되고있다. 3 본연구에서합성한캡슐역시첨가한가교제에의해서이러한형상을가지는것으로판단된다. Potassium persulfate, sodium bisulfate Table 1. Comparison of Expandable Properties Properties None Potassium persulfate bisulfite sulfide T start ( o C) T max ( o C) D max (µm) Particle size (µm) Figure 3. TMA for thermally expandable microspheres prepared with different post-treatment. 로후처리한경우, 후처리전의열팽창성미소구 Figure 4(a) 와이미지상에서특이점이보이지않으나 sodium sulfide를이용하여후처리를진행한경우 Figure 4(d) 의이미지와같이, 열팽창성미소구입자의외곽이붕괴되어내부의팽창제역할을하는탄화수소가유출됨에따라열을가해도발포가거의이루어지지않은것으로판단된다. 3. PVC 졸발포시험 벽지분야에열팽창성미소구가적용될시가장많이사용되는매질인 PVC 졸에적용하기위해, 각각의개시제로후처리전후열팽창성미소구들을 PVC 졸에서발포시켜얻어진발포배율과색차계분석결과를 Table 2에나타내었고, 후처리하지않은열팽창성미소구의경우발포배율은 230배였으며, potassium persulfate, sodium bisulfite로처리한미소구의발포배율은다소증가한경향을보였다. 반면 sodium sulfide 로후처리한시편은거의발포가이루어지지않았다. 황변값을의미하는 b값은 sodium bisulfite, potassium persulfate, none, sodium sulfide 순으로낮았으며, WI의경우는 sodium bisulfite, none, potassium persulfate, sodium sulfide 순으로높았다. 이결과로 sodium bisulfite로후처리한열팽창성미소구가발포배율물성이높으면서, 백색도향상및황변의변화정도가낮은것을확인할수있다. 4. bisulfite 함량에따른특성변화 bisulfite로후처리후, PVC 졸시험에서높은발포배율과백색도및황변에있어서우수한성능을보임에따라함량별로달리처리한열팽창성미소구들의 TMA curve를 Figure 5에나타내었으며, 그결과를정리하여 Table 3에나타

214 Hae Na You et al. / Elastomers and Composites Vol. 52, No. 3, pp. 211-215 (September 2017) Figure 4.

4 214 Hae Na You et al. / Elastomers and Composites Vol. 52, No. 3, pp (September 2017) Figure 4. SEM images ( 500, 2500) of thermally expandable microspheres (a) None, (b) Potassium persulfate, (c) bisulfite, and (d) sulfide. Table 2. Results of PVC Sol Test Properties None Expansion ratio (%) 230 Potassium persulfate bisulfite sulfide 140 Whiteness index (WI) Yellowing (b) 내었다. Table 3에서 보듯이 2 wt% 함량이 투입 되었을때, 가 장 높은 체적변화를 나타내었다. 또한, Table 3에 나타나 있는 입자 크기의 경우, 2 wt% 함 량의 sodium bisulfite로 열팽창성 미소구를 후처리 하였을 때 가장 작은 입자 크기를 확인 할 수 있었다. Conclusion 열팽창성 미소구가 poly(vinyl chloride) 등의 매질에서 우수 한 발포배율과 백색도를 향상시키기 위해서 중합후 potassium

5 A Study of Characteristics Variation of Thermally Expandable Microspheres in Post-polymerization Treatment by Various Initiators 215 References Figure 5. Effect of bisulfite contents to the expandable properties. Table 3. Effect of Bisulfite Content to the Expandable Property and Particle Size Content (wt%) T start ( o C) T max ( o C) D max (µm) Particle size (µm) persulfate, sodium bisulfite, 그리고 sodium sulfide의개시제로후처리하였다. Potassium persulfate와 sodium bisulfite를사용하여후처리한경우에는발포거동에큰차이가없었으며, sodium sulfide로후처리한경우에는발포가거의일어나지않았다. bisulfite를사용한경우에는백색도및황변도가다른개시제로후처리한경우보다우수하였다. PVC 졸매질에서발포배율이가장우수하면서, 백색도향상및황색변화정도가적었던 sodium bisulfite를첨가량에변화를주어시험을진행하였고, 그중 2wt% 처리한경우에체적변화율이가장좋았으며, 이로부터제조된열팽창성미소구는우수한발포성과백색도를제공할수있어, 코팅, 벽지분야에다양하게적용할수있을것으로기대된다. Acknowledgments 본연구는중소기업청의월드클래스300프로젝트 R&D지원사업 (S ) 의지원을받아수행된연구입니다. 1. M. Jonsson, O. Nordi, A. L. Kron, and E. Malmström, Thermally expandable microspheres with excellent expansion characteristics at high temperature, J. Appl. Polym. Sci., 117, 384 (2010). 2. Y. Kawaguchi and T. Oishi, Synthesis and properties of thermoplastic expandable microspheres: The relation between crosslinking density and expandable property, Journal of Applied Polymer Science, 93, 505 (2004). 3. M. Jonsson, D. Nyström, O. Nordin, and E. Malmström, Surface modification of thermally expandable microspheres by grafting poly (glycidyl methacrylate) using ARGET ATRP, European Polymer Journal, 45, 2374 (2009). 4. J. H. Bu, Y. S. Kim, J. U. Ha, and S. E. Shim, Suspension Polymerization of Thermally Expandable Microcapsules with Core-Shell Structure Using the SPG Emulsification Technique: Influence of Crosslinking Agents and Stabilizers, Polymer(Korea), 39, 78 (2015). 5. Y. Kawaguchi, Y. Itamura, K. Onimura, and T. Oishi, Effects of the chemical structure on the heat resistance of thermoplastic expandable microspheres, Journal of Applied Polymer Science, 96, 1306 (2005). 6. P. Ilundain, D. Alvarez, L. Da Cunha, L. R. Salazar, M. J. Barandiaran, and J. M. Asua, Knowledge-based choice of the initiator type for monomer removal by postpolymerization, Journal of Polymer Science Part A: Polymer Chemistry, 40, 4245 (2002). 7. P. H. H. Araújo, C. Sayer, R. Giudici, and J. G. Poco, Techniques for reducing residual monomer content in polymers: a review, Polymer Engineering & Science, 42, 1442 (2002). 8. R. Khesareh, N. T. McManus, and A. Penlidis, High temperature bulk copolymerization of methyl methacrylate and acrylonitrile: II. Full conversion range experiments, Journal of Macromolecular Science, 43, 23 (2006). 9. R. Salazar, P. Ilundain, D. Alvarez, L. Da Cunha, M. J. Barandiaran, and J. M. Asua, Reduction of the residual monomer and volatile organic compounds by devolatilization, Industrial & Engineering Chemistry Research, 44, 4042 (2005). 10. A. Kumar, B. Prasad, and I. M. Mishra, Optimization of process parameters for acrylonitrile removal by a low-cost adsorbent using Box-Behnken design, Journal of Hazardous Materials, 150, 174 (2008).

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12.077~081(A12_이종국).fm J. of Advanced Engineering and Technology Vol. 1, No. 1 (2008) pp. 77-81 y w» e wx Á w œw Fabrication of Ceramic Batch Composition for Porcelain by Using Recycled Waste Ceramic Powder Hyun Guen Han, and