The mechanism of roughness-induced CO2 microbubble nucleation in polypropylene foaming,Physical Chemistry Chemical Physics

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The mechanism of roughness-induced CO2 microbubble nucleation in polypropylene foaming
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2017-07-13 00:00:00 , DOI: 10.1039/c7cp02988h
Linyan Wang _{1,

2,

3,

4,

5} , Wei Zhang _{4,

5,

6} , Xiangdong Wang _{1,

2,

3,

4} , Jianguo Mi _{3,

4,

7,

8,

9} , Jingjun Ma _{4,

5,

6} , Zhongjie Du _{3,

4,

7,

8,

9}

Affiliation

Within the framework of classical density functional theory, the thermodynamic driving forces for CO₂ microbubble nucleation have been quantitatively evaluated in the foaming of polypropylene containing amorphous and crystalline structures. After the addition of fluorinated polyhedral oligomeric silsesquioxane particles into the polypropylene matrix, we construct different composite surfaces with nanoscale roughness for bubble nucleation. Meanwhile, as the dissolved CO₂ molecules increase, the corresponding CO₂/PP binary melts can be formulated in the systems. Due to the roughness effect coupled with the weak interactions of particle–PP, PP chains in the binary melts are depleted from the surfaces, leading to a significant enhancement of osmotic pressure in depletion regions. During the foaming process, a large number of dissolved CO₂ molecules are squeezed into the regions, thus local supersaturations are dramatically improved, and the energy barriers for bubble nucleation are dramatically reduced. Moreover, when the nanocomposite surfaces display ordered nanoscale patterns, the energy barriers can be further reduced to their respective minimum values, and the bubble number densities reach their maximum. Accordingly, the bubble number densities can be enhanced by 4 or 5 orders of magnitude for bubbles nucleated on the crystalline or amorphous PP nanocomposite surface. In contrast, when the foaming pressure is increased from 15 to 20 MPa, the elevated bubble number density in the foaming PP matrix is less than one order of magnitude. As a result, the enhancement of local supersaturation induced by the controlled nanoscale roughness is much more effective than that of bulk supersaturation given by high pressure.

中文翻译：

聚丙烯泡沫中粗糙度引起的CO ₂微泡成核机理

在经典密度泛函理论的框架内，已经对包含无定形和晶体结构的聚丙烯的发泡过程中的CO ₂微泡成核的热力学驱动力进行了定量评估。将氟化多面体低聚倍半硅氧烷颗粒添加到聚丙烯基质中后，我们构建了具有纳米级粗糙度的不同复合表面，用于气泡成核。同时，随着溶解的CO ₂分子增加，相应的CO ₂/ PP二元熔体可以在系统中配制。由于粗糙效应和颗粒-PP的弱相互作用，二元熔体中的PP链从表面耗尽，导致耗尽区的渗透压显着提高。在发泡过程中，大量溶解的CO ₂分子被压入这些区域，从而显着改善了局部过饱和，并显着降低了气泡成核的能垒。此外，当纳米复合材料表面显示有序的纳米级图案时，能垒可以进一步减小至其各自的最小值，并且气泡数密度达到其最大值。因此，对于在结晶或无定形PP纳米复合材料表面上成核的气泡，气泡数密度可以提高4或5个数量级。相反，当发泡压力从15MPa增加到20MPa时，发泡PP基体中升高的气泡数密度小于一个数量级。因此，

更新日期：2017-08-09

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