Biobased auxetic foams: an assessment of manufacturing and multifunctional properties

营养生长是一类机械超材料，其泊松比为负值；也就是说，当纵向延伸时，它们会横向扩张。具有拉伸特性的泡沫塑料还具有抗剪切压痕、循环准静态和动态载荷下的能量吸收、抗低动能冲击、在相对湿度条件下增强的动态弹性系数和可定制的形状记忆性能等其他理想特性。多年来，已经开发了多种制造工艺来将传统泡沫塑料转化为辅助剂，从热机械(包括体积压缩、热处理和冷却)到化学处理(利用丙酮和二氧化碳来软化泡沫细胞壁)。然而，到目前为止，还没有人为知晓而生产出人造泡沫超材料。生物基聚氨酯(和相关泡沫)的最新发展使生产生物基负泊松比泡沫材料成为一种明显的可能性。植物油多元醇(如蓖麻油和大豆油)最近被用于不同的混合物中，通过在实验室和商业规模上自由上升来生产基于生物的开孔和闭孔泡沫，与基于化石的多元醇相比，表现出更好的压缩和热性能。由生物基基质制成的膨胀性泡沫将进一步增加在广泛应用中使用这类超材料的吸引力，因为与化石材料相比，这种材料具有更好的生命周期特性和全球变暖功率。此外，膨胀型生物泡沫也将是第一批从一开始就被设计为可持续和环保的机械超材料产品之一。这种材料的潜在应用范围从航空航天工业，其中增强的抗冲击性和轻量化将有助于提高效率，到跑鞋、头盔和垫子中的运动设备，这将受益于此类材料的独特性能。在此背景下，该项目的目标是：-从化学、热和形态方面表征可用的蓖麻和豆油基PU泡沫，结合机械(准静态、动态和粘弹性)，声学和振动测试。-通过不同的转化途径制造生物基伸展开孔和闭孔超材料泡沫。-通过研究形态以及遵循实验程序设计的机械、声学和振动响应来评估通过不同工艺获得的伸展泡沫的生存能力。-调整现有的泡沫力学、振动和声学的本构模型，以描述这些新类别的生物基超材料的相应特性。

Auxetics are a class of mechanical metamaterials exhibiting a negative Poisson's ratio; that is, they expand laterally when extended longitudinally. Foams with auxetic characteristics also possess other desirable features in terms of indentation resistance to shear, energy absorption under cyclic quasi-static and dynamic loading, resistance to low kinetic energy impact, the enhanced dynamic modulus under relative humidity conditions, and tailorable shape memory properties. Over the years, multiple manufacturing processes have been developed to transform conventional foams into auxetics, ranging from thermo-mechanical (involving volumetric compression, annealing, and cooling) to chemical treatments (exploiting acetone and carbon dioxide to soften foam cell walls). No artificial auxetic foam metamaterial has, however, so far been knowingly produced.Recent developments in bio-based polyurethanes (and related foams) make producing bio-based negative Poisson's ratio foam materials a distinct possibility. Vegetable oil-based polyols (such as castor oil and soybean oil) have been recently used in different blends to produce biobased open- and closed-cell foams via free-rising both at the laboratory scale and commercially, showing improved compression and thermal properties compared to fossil-based counterparts. An auxetic foam made of bio-based substrates would further increase the appeal of using this class of metamaterials in a wide range of applications because of the enhanced life cycle properties and global warming power reduction compared to their fossil counterparts. Moreover, auxetic biobased foams would also be among the first mechanical metamaterial products designed to be sustainable and eco-friendly from the onset. Potential applications of such materials range from the aerospace industry, where enhanced impact resistance and lightweight would contribute to improved efficiency, to sports equipment in running shoes, helmets, and padding, which would benefit from the unique properties of this class of materials.In this context, the objectives of this project are:- Characterise available castor and soy oil-based PU foams from the chemical, thermal, and morphological aspects, combined with mechanical (quasi-static, dynamic, and viscoelastic), acoustic and vibration testing.- Manufacture biobased auxetic open- and closed-cell metamaterial foams through different conversion routes.- Assess the viability of the auxetic foams obtained through the different processes by investigating the morphology and the mechanical, acoustic and vibration responses following a Design of Experiment procedure.- Adapt existing constitutive models available for foams' mechanics, vibration, and acoustics to describe the corresponding properties of these new classes of biobased metamaterials.