Flow‐induced oriented crystals have attracted considerable attention because they significantly increase stiffness and strength of polymer products. Naturally, understanding the necessary condition of forming oriented crystals is of importance for both industry and polymer physics. Following the concept of specific work of flow proposed by Mykhaylyk and co‐workers, the expression of the specific work of flow, w _(T,P), was carefully summarized and verified that when w _(T,P) is above a critical specific work of flow, w _c(T,P) = (1.7 ± 0.7) × 10⁷ J m⁻³, oriented crystals in isotactic polypropylene can be induced by flow at pressures (50, 100, and 150 MPa) and at a undercooling of 65 K. The influences of pressure on w _c(T,P) stem from two facets: one is the influence on the melt viscosity (the Barus law), and the other one is the influence on the equilibrium melting temperature (the Clapeyron equation). The current study can guide real processing to fabricate high‐performance polymer products with oriented crystals.

中文翻译：

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压力下全同立构聚丙烯中流致取向晶体的判据

流动诱导取向的晶体已经引起了相当大的关注，因为它们显着提高了聚合物产品的刚度和强度。自然地，了解形成定向晶体的必要条件对工业和聚合物物理学都很重要。遵循Mykhaylyk及其同事提出的流量特定功的概念，仔细总结了流量特定功w _{（T，P）的表达}，并验证了当w _（T，P）高于临界特定流量时流量功w _c（T，P） =（1.7±0.7）×10 ⁷ J m ^-3在压力（50、100和150 MPa）和过冷65 K的条件下，流动会诱发等规聚丙烯中的取向晶体。压力对w _{c（T，P）的影响}来自两个方面：一个是对熔融粘度的影响（巴鲁斯定律），另一个对平衡熔融温度的影响（克拉佩龙方程）。当前的研究可以指导实际加工，以制造具有定向晶体的高性能聚合物产品。