Selective cross-linking of oligosilazanes to tailored meltable polysilazanes for the processing of ceramic SiCN fibres
Selective cross-linking of oligosilazanes to tailored meltable polysilazanes for the processing of ceramic SiCN fibres
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DOI：
10.1039/c3ta13254d
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发表时间：
2013-01-01
影响因子：
11.9
通讯作者：
Motz, Guenter
中科院分区：
文献类型：
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作者：
Flores, Octavio;Schmalz, Thomas;Motz, Guenter
以四正丁基氟化铵(TBAF)为催化剂，通过N-H和Si-H基团选择性交联，将不同的商用液体低聚硅氮烷(ML33和HTT1800)改性为聚硅氮烷，开发了一种有趣的非氧化物陶瓷纤维加工替代方案，其成本低于目前商业上可用的纤维类型。通过终止与硼氢化钙的反应，可以加工具有量身定制的化学和热性能的可熔融固体聚硅氮烷(ML33S和HTTS)，以满足机械稳定且均匀的聚合物纤维的熔融纺丝要求。用凝胶渗透色谱(GPC)、差示扫描量热法(DSC)和流变仪研究了聚硅氮烷ML33S和HTTS的化学稳定性和热稳定性。这些技术表明了分子量和玻璃化温度对催化交联剂条件的依赖性。熔融纺丝过程中，聚合物的玻璃化-液体转变温度(Tg)介于65℃到81℃之间，具有粘弹性，这是熔融纺丝工艺的基本特性。ML33S的热稳定性可确保高达220℃。相比之下，由于乙烯基团的存在，HTTS的热稳定性被限制在170℃。通过振荡流变仪测量聚合物熔体的粘弹行为，以及足够的热稳定性，允许在110-130℃的温度范围内通过熔融纺丝连续加工稳定的绿色纤维。在快速电子束辐照后，ML33S和HTTS聚硅氮烷的绿色纤维固化和连续的非晶态陶瓷SiCN纤维的热解成功地合成了，而定义的T-g点对形状和光滑度有积极的影响。
An interesting alternative for the processing of non-oxide ceramic fibres at lower costs than that for the current commercially available fibre types was developed by modifying different commercially available liquid oligosilazanes (ML33 and HTT1800) into polysilazanes by selective cross-linking via the N-H and Si-H groups with tetra-n-butylammoniumfluoride (TBAF) as a catalyst. Termination of the reaction with calcium borohydride allows the processing of meltable solid polysilazanes (ML33S and HTTS) with tailored chemical and thermal properties, to fulfil the requirements for the melt spinning of mechanically stable and homogeneous polymeric fibres. The chemical and thermal stability of the polysilazanes ML33S and HTTS were investigated by using GPC, DSC and rheological measurements. These techniques indicate the dependency of the molecular weight and glass temperature on the catalytical cross-linking conditions. Polymers with up to similar to 10 000 g mol(-1) show glass-liquid transition (Tg) between 65 and 81 degrees C and viscoelasticity, which are essential properties for the melt-spinning process. The thermal stability of ML33S is ensured up to 220 degrees C. In contrast the thermal stability of HTTS is limited to 170 degrees C due to the presence of vinyl-groups. The viscoelastic behaviour of the polymer melts, measured by oscillatory rheometry, and the sufficient thermal stability allowed the continuous processing of stable green fibres by melt spinning in the temperature range of 110 to 130 degrees C. After fast electron beam irradiation curing of the green fibres and pyrolysis of continuous amorphous ceramic SiCN fibres from both ML33S and HTTS polysilazanes were successfully synthesized, while a defined T-g point influences the shape and the smoothness positively.