Tao Ran, Zhang Fan, Nguyen Huong Giang, Bernstein Philip, Forster Amanda L, Mrozek Randy A, Forster Aaron M
Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
Department of Chemical Engineering, Texas Tech University, Lubbock, TX 70409, USA.
J Mater Sci. 2021;56(29). doi: 10.1007/s10853-021-06334-x.
In this work, different formulations of a room-temperature silicone composite backing material (SCBM) composed of polydimethylsiloxane (PDMS), fumed silica and corn starch were investigated using different characterization techniques, i.e., differential scanning calorimetry, thermogravimetry analysis, X-ray diffraction (XRD) and small-angle X-ray scattering, as a function of controlled relative humidity. At ambient relative humidities in the range of about 20-80%, the equilibrium water content in the SCBM ranges from approximately 4-10%, which is predominantly absorbed by the corn starch. This amount of water content has been shown to have minimal effect on thermal transition temperatures (melting and glass transition) of the SCBMs. The enthalpy of melting increases with increasing relative humidity, which reflects the heterogeneous semicrystalline structure of starch granules and the role of moisture in facilitating the formation of amylopectin double helices mainly in the imperfect crystalline regions. The thermal degradation of SCBM exhibits three major mass loss steps that correspond to dehydration, decomposition of corn starch and decomposition of PDMS. The XRD patterns reveal a characteristic diffuse peak for amorphous PDMS and an A-type crystallinity for the corn starch. The XRD results show no observable changes in the crystal type and crystallinity as a function of moisture content. Results from this work help clarify the fundamental structure-property relationships in SCBMs, which are important for future development of documentary standards, especially the handling and storage specifications of next-generation ballistic witness materials for body armor testing.
在本研究中，使用差示扫描量热法、热重分析、X射线衍射（XRD）和小角X射线散射等不同表征技术，研究了由聚二甲基硅氧烷（PDMS）、气相二氧化硅和玉米淀粉组成的室温硅酮复合背衬材料（SCBM）的不同配方，该配方是相对湿度的函数。在约20 - 80%的环境相对湿度范围内，SCBM中的平衡水分含量约为4 - 10%，主要由玉米淀粉吸收。已表明该水分含量对SCBM的热转变温度（熔点和玻璃化转变温度）影响最小。熔化焓随相对湿度增加而增加，这反映了淀粉颗粒的非均相半结晶结构以及水分在促进支链淀粉双螺旋形成中的作用，主要是在不完善的结晶区域。SCBM的热降解表现出三个主要的质量损失步骤，分别对应于脱水、玉米淀粉分解和PDMS分解。XRD图谱显示无定形PDMS的特征漫射峰和玉米淀粉的A型结晶度。XRD结果表明，晶体类型和结晶度不会随水分含量发生明显变化。本研究结果有助于阐明SCBM中的基本结构 - 性能关系，这对于未来文献标准的制定非常重要，特别是对于下一代用于防弹衣测试的弹道见证材料的处理和存储规范。
