Nanofiber toughened polyethylene composites
Nanofiber toughened polyethylene composites
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DOI：
10.1016/j.carbon.2004.03.021
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发表时间：
2004
期刊：
影响因子：
10.9
通讯作者：
K. Lozano;Shuying Yang;Robert Jones
中科院分区：
文献类型：
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作者：
K. Lozano;Shuying Yang;Robert Jones
纳米纤维/纳米管（NF/NT）增强聚合物复合材料因其潜在的高科技应用而被广泛研究。在电气和物理领域已经取得了有吸引力的成果，而结构增强的潜力仍然被认为是一项重大技术挑战，因此引起了研究和工业界的高度关注[1-5]。大多数报告的工作表明，随着失效应变的损失，强度和刚度略有改善（未达到预期）[6-12]。最近，对高性能 NF/NT 聚合物复合材料的研究在韧性增强方面取得了成功的结果。道尔顿等人[13]发表了通过基于凝固的纺丝方法与聚乙烯醇相关的“超韧”碳纳米管（CNT）纤维。在这里，我们展示了极高的延展性、高韧性、中等强度的碳纳米纤维（CNF）增强聚乙烯块状复合材料。超过 1600% 的总拉伸伸长率高于纳米增强复合材料的任何已公布值，并且高于任何给定材料的上限 (1000%) [14]。我们开发了一种用纯化的气相生长 CNF 增强的高密度聚乙烯 (HDPE) 基质。密度和熔体流动指数分别为 0.95 g/cc 和 10 g/10 分钟的 HDPE 购自 Phillips, Inc.。 NF（Pyrograph III PR-19-raw，直径范围在 40 至 150 nm 之间）由 Applied Sciences, Inc. 友情提供，由于其更广泛的可用性和更低的成本，可用作 CNT 的模型系统。 CNF 由高度石墨化结构组成，该结构由通过碳化学气相沉积工艺增厚的内部细丝（直径 10 nm）组成。 CNF 的长度可以在 50 到 100 lm 之间变化，因此可以获得高纵横比 [15]。正如之前报道的那样，NFs经过纯化和功能化以去除无定形碳并打开高度缠结的纤维[16]。含有 8 wt.% 纳米纤维的复合材料通过混合、挤出和压缩成型在熔体中反复受到剪切力。 CNF 在 HDPE 中的分散和分布是通过在 Haake Rheomixer 600 小型密炼机中在 180°C、速度为 60 rpm、混合时间为 10 分钟下混合各组分来实现的。将复合材料在200℃、27MPa的压力下压制1.5分钟并造粒。使用具有狭缝毛细管模头的单螺杆挤出机挤出颗粒。在相同条件下再次压制挤出物并切割以进行拉伸测试。拉伸性能根据 ASTM D882 进行测量，其中标距长度为 5.08 厘米、厚度为 0.56 毫米的哑铃样品在 MTS Sintech 65/G 中以 50.8 毫米/分钟的十字头速度进行测试。我们开发了具有极其良好润湿纤维的各向同性片材，经扫描电子显微照片验证（图 1A 和 B）。由于样品达到了拉伸测试仪的最大容量（66 厘米）而没有出现故障，因此无法获得复合材料的拉伸伸长率和韧性（应力-应变曲线下的面积）的精确值。获得了 1300% 的失效应变和 151 kJ/m2 的韧性结果，屈服强度为 25 MPa，弹性模量为 800 MPa。切割并重新测试细长样品的碎片。样品能够额外伸长 24%，韧性为 6.5 kJ/m2，模量为 1600 MPa，屈服强度为 232 MPa。通过将我们开发的系统与纯 HDPE 样品进行比较（图 2），伸长率提高了至少 220%，模量提高了 60%，韧性提高了 290%。与我们之前准备的相比
Nanofiber/nanotube (NF/NT) reinforced polymer composites have been widely studied because of their potential high-technological applications. Attractive results in the electrical and physical fields have been obtained while the potential of structural enhancements is still considered a major technological challenge and therefore of high interest in the research and industrial communities [1–5]. Most of the reported work shows small (not as expected) improvements in strength and stiffness with loss of strain to failure [6–12]. Recently, the search for high performance NF/NT polymer composites produced successful results in relation to toughness enhancements. Dalton et al.[13] published ‘‘super-tough’’carbon-nanotube (CNT) fibers associated with polyvinyl alcohol through a coagulation-based spinning method. Here, we show extremely high extensibility, high toughness, moderate strength, carbon nanofiber (CNF) reinforced polyethylene bulk composites. The total tensile elongation of more than 1600% is higher than any published value for nanoreinforced composites and higher than the upper bound (1000%) for any given material [14]. We developed a high-density polyethylene (HDPE) matrix reinforced with purified vapor grown CNFs. HDPE with a density and melt flow index of 0.95 g/cc and 10 g/10 min respectively was obtained from Phillips, Inc. NFs (Pyrograph III PR-19-raw with diameters ranging between 40 and 150 nm) were kindly supplied by Applied Sciences, Inc. and used as a model system for CNT given their wider availability and lower cost. CNFs consist of a highly graphitic structure that is composed of an inner filament (diameter of 10 nm) thickened by a carbon chemical vapor deposition process. The length of CNFs can vary between 50 and 100 lm, therefore high aspect ratios can be obtained [15]. The NFs, as previously reported, were purified and functionalized to remove amorphous carbon and to open the highly tangled fibers [16]. The composite with 8 wt.% of nanofibers was repeatedly subjected to shear forces in the melt through mixing, extrusion, and compression molding. Dispersion and distribution of the CNFs in the HDPE was achieved by mixing the components in a Haake Rheomixer 600 miniaturized internal mixer at 180 C, with a speed of 60 rpm and a mixing time of 10 min. The composite was pressed at 200 C at a pressure of 27 MPa for 1.5 min and pelletized. The pellets were extruded using a single screw extruder with a slit capillary die. The extrudate was re-pressed under the same conditions and cut for tensile testing. Tensile properties were measured according to ASTM D882 where dumbbell specimens of 5.08 cm in gage length and 0.56 mm thick were tested in a MTS Sintech 65/G at a crosshead speed of 50.8 mm/min. We developed isotropic sheets with extremely well wetted fibers as verified in scanning electron micrographs (Fig. 1A and B). Exact values for tensile elongation and toughness (area under the stress–strain curve) of the composites were not obtained since the samples reached the maximum capacity of our tensile tester (66 cm) without failure. Results of 1300% for strain to failure and 151 kJ/m2 for toughness, with yield strength of 25 MPa and elastic modulus of 800 MPa were obtained. Pieces of the elongated samples were cut and retested. The samples were able to elongate an additional 24% with a toughness of 6.5 kJ/m2, a modulus of 1600 MPa and yield strength of 232 MPa. By comparing our developed system with pure HDPE samples (Fig. 2), increases of at least 220% in elongation, 60% in modulus and 290% in toughness were obtained. When compared to our previous prepared