Tailoring the dispersion of multiwall carbon nanotubes in co-continuous PVDF/ABS blends to design materials with enhanced electromagnetic interference shielding

Highly conducting composites were derived by selectively localizing multiwall carbon nanotubes (MWNTs) in co-continuous PVDF/ABS (50/50, wt/wt) blends. The electrical percolation threshold was obtained between 0.5 and 1 wt% MWNTs as manifested by a dramatic increase in the electrical conductivity by about six orders of magnitude with respect to the neat blends. In order to further enhance the electrical conductivity of the blends, the MWNTs were modified with amine terminated ionic liquid (IL), which, besides enhancing the interfacial interaction with PVDF, facilitated the formation of a network like structure of MWNTs. This high electrical conductivity of the blends, at a relatively low fraction (1 wt%), was further explored to design materials that can attenuate electromagnetic (EM) radiation. More specifically, to attenuate the EM radiation by absorption, a ferroelectric phase was introduced. To accomplish this, barium titanate (BT) nanoparticles chemically stitched onto graphene oxide (GO) sheets were synthesized and mixed along with MWNTs in the blends. Intriguingly, the total EM shielding effectiveness (SE) was enhanced by ca. 10 dB with respect to the blends with only MWNTs. In addition, the effect of introducing a ferromagnetic phase (Fe3O4) along with IL modified MWNTs was also investigated. This study opens new avenues in designing materials that can attenuate EM radiation by selecting either a ferroelectric (BT-GO) or a ferromagnetic phase (Fe3O4) along with intrinsically conducting nanoparticles (MWNTs).

Simultaneous enhancement in mechanical strength, electrical conductivity, and electromagnetic shielding properties in PVDF-ABS blends containing PMMA wrapped multiwall carbon nanotubes

A unique approach was adopted to drive the multiwall carbon nanotubes (MWNTs) to the interface of immiscible PVDF-ABS blends by wrapping the nanotubes with a mutually miscible homopolymer (PMMA). A tailor made interface with an improved stress transfer was achieved in the blends with PMMA wrapped MWNTs. This manifested in an impressive 108% increment in the tensile strength and 48% increment in the Young's modulus with 3 wt% PMMA wrapped MWNTs in striking contrast to the neat blends. As the PMMA wrapped MWNTs localized at the interface of PVDF-ABS blends, the electrical conductivity could be tuned with respect to only MWNTs, which were selectively localized in the PVDF phase, driven by thermodynamics. The electromagnetic shielding properties were assessed using a vector network analyser in a broad range of frequency, X-band (8-12 GHz) and Ku-band (12-18 GHz). Interestingly, enhanced EM shielding was achieved by this unique approach. The blends with only MWNTs shielded the EM waves mostly by reflection however, the blends with PMMA wrapped MWNTs (3 wt%) shielded mostly by absorption (62%). This study opens new avenues in designing materials, which show simultaneous improvement in mechanical, electrical conductivity and EM shielding properties.

ABS树脂形态结构及力学性能的研究

ABS树脂具有优良的抗冲击性、耐热性和耐化学药品性，还具有易加工性、制品尺寸稳定性等特点，广泛应用于工业领域。ABS树脂的制备方法有许多种，目前应用最为广泛的是乳液接枝ABS共聚物一本体SAN掺混法。首先采用乳液聚合方法合成聚丁二烯胶乳，然后将其作为种子进行苯乙烯和丙烯睛的接枝共聚反应生成ABS接枝共聚物；采用本体法制备SAN树脂；最后将ABS接枝共聚物（冲击改性剂）和SAN树脂共混制得ABS树脂。由此看来，ABS接枝共聚物的合成是控制ABS树脂性能的关键。目前国产ABS树脂普遍存在的问题是ABS接枝共聚物的增韧效率低。影响其增韧效率的因素包括共聚单体的组成、橡胶相的组成及结构、橡胶与树脂之间的界面结合力等。因此为提高ABS冲击改性剂的增韧效率，拓宽ABS树脂的应用领域，应合理地控制ABS冲击改性剂的合成参数。本论文采用种子乳液聚合方法在PB（聚丁二烯）橡胶粒子上接枝共聚苯乙烯和丙烯睛合成ABS接枝共聚物，将其作为冲击改性剂与SAN树脂共混制备ABS树脂，对ABS树脂形态结构及力学性能进行了研究。主要研究内容和结论如下：1、研究ABS接枝共聚物中PB／SAN组成、TDDM（叔十二碳硫醇）链转移剂和CHP（过氧化氢异丙苯）用量、单体加料方式及引发剂类型对SAN在PB橡胶粒子上接枝度的影响。sAN在PB橡胶粒子上的接枝度随PB和TDDM含量的增加而降低；随CHP用量的增加先增加后降低；随单体滴加时间的延长而增加，但过分延长时间则对接枝度影响很小；与AIBN（偶氮二异丁睛）和K25208（过硫酸钾）相比，采用氧化一还原引发体系得到的接枝度较高。2、研究ABS接枝共聚物的力学性能。DMA结果表明，随着PB含量的增加，ABS接枝共聚物的储能模量降低，橡胶相的玻璃化转变温度向低温移动，内耗峰值增加。拉伸试验结果表明，当体系中没有TDDM时，不同橡胶含量的ABS接枝共聚物均没有发生明显的应变软化；当加入适量的TDDM后，材料发生应变软化，且随着TDDM用量的增加，材料的屈服应力提高。3、研究ABS接枝共聚物对ABS树脂形态结构及力学性能的影响。ABS接枝共聚物中PB／SAN组成及TDDM链转移剂用量影响ABs树脂中橡胶粒子的内部形态及橡胶粒子在基体中的分散。在合成ABS接枝共聚物的过程中，应合理地调节PB／SAN组成及TDDM的用量以使ABS接枝共聚物达到最大的增韧效率。4、研究ABS树脂在不同应变速率下的断裂行为及形变机理。结果表明，橡胶含量及应变速率影响ABS树脂的力学性能，但没有改变ABS树脂的形变机理。ABS树脂的形变机理包括银纹、橡胶粒子的空洞化及基体的剪切屈服，其中占主导地位的是橡胶粒子的空洞化及基体的剪切屈服。

PVC/ABS共混系统力学性能的研究

用冲击试验机、材料试验机和另外一些相关的仪器对PVC/ABS共混体系的力学性能进行了测试、研究,结果发现,PVC/ABS共混体系的性能是组分的函数.ABS的加入改善了PVC/ABS共混体系的力学性能,随着ABS的增加,体系的冲击强度和断裂伸长率明显地提高,而体系的拉伸强度、拉伸模量几乎是随ABS含量的增加而单调地下降.

Transition from crazing to shear deformation in ABS/PVC blends

ABS/PVC blends were prepared over a range of compositions by mixing PVC, SAN, and PB-g-SAN. All samples were designed to have a constant rubber level of 12 wt % and the ratio of total-SAN to PVC in the matrix of the blends varied from 70.5/17.5 to 18/80. Transmission electron microscope and scanning electron microscope have been used to study deformation mechanisms in the ABS/PVC blends. Several different types of microscopic deformation mechanisms, depending on the composition of blends, were observed for the ABS/PVC blends. When the blend is a SAN-rich system, the main deformation mechanisms were crazing of the matrix. When the blend is a PVC-rich system, crazing could no longer be detected, while shear yielding of the matrix and cavitation of the rubber particles were the main mechanisms of deformation. When the composition of blend is in the intermediate state, both crazing and shear yielding of matrix were observed. This suggests that there is a transition of deformation mechanism in ABS/PVC blends with the change in composition, which is from crazing to shear deformation.