مروری بر پیرسازی فیزیکی و نوسازی گرمایی و مکانیکی در پلیمرهای بی‌شکل شیشه‌ای

نوع مقاله : تالیفی

نویسندگان

1 پژوهشگاه پلیمر و پتروشیمی ایران

2 دانشجوی کارشناسی ارشد پژوهشگاه پلیمر و پتروشیمی ایران

چکیده

پیرسازی فیزیکی و نوسازی از حالت پیرشده پس از معرفی توسط Struik برای اولین بار، مورد توجه بسیاری از پژوهشگران قرار گرفته است. پیرسازی فیزیکی موجب می‌شود تا پلیمر بی‌شکلی که در زیر دمای انتقال شیشه‌ای از حالت تعادل دور است، به‌سمت تعادل حرکت کند. مشاهده شده است، این پدیده خواص پلیمرهای بی‌شکل شیشه‌ای را تغییر می‌دهد. اما با اعمال چرخه گرمایی با عنوان نوسازی گرمایی، این تغییرات از حافظه پلیمر پاک می‌شود و پلیمر به حالت غیرتعادلی بازمی‌گردد. شبیه‌سازی‌های تجربی و  ریاضی بسیاری نیز روی خواص گوناگون پلیمرها به‌منظور مشاهده پاک‌شدن یا نشدن این تغییرات در اثر اعمال تنش‌های مکانیکی با عنوان نوسازی مکانیکی، در رژیم‌های پیش و پس از تسلیم پلیمر انجام شده است. اما با توجه به تضاد نتایج به‌دست آمده، همچنان نمی‌توان رخداد یا عدم رخداد نوسازی مکانیکی را اثبات کرد. با وجود گذشت نزدیک به چهار دهه از معرفی این پدیده، هیچ‌گونه بررسی و جمع‌بندی از نتایج پژوهشگران در این زمینه ارائه نشده است. در این مقاله پس از معرفی کلی پدیده پیرسازی فیزیکی، اثر این پدیده بر خواص پلیمرهای بی‌شکل شیشه‌ای به‌اختصار توضیح داده می‌شود. در ضمن، نتایج به‌دست آمده از پژوهش‌ها و مطالعات پژوهشگران مختلف در باره نوسازی گرمایی و مکانیکی و دلایل دست‌یابی به آن‌ها هم بررسی می‌شود.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Physical Aging and Thermal and Mechanical Rejuvenation in Glassy Amorphous Polymers: A Review

نویسندگان [English]

  • Mohammad Razavi-Nouri 1
  • Ali Taslimi 2
1
2
چکیده [English]

The term "physical aging" was first coined by Struik to separate the relaxation of glassy polymers from those of other time-dependent phenomena such as chemical aging. Glassy amorphous polymers are in non-equilibrium states below their glass transition temperature (Tg). A glassy polymer gradually moves toward its equilibrium state with time when it is kept below Tg. The amorphous polymer can be heated again, known as thermal rejuvenation, to erase its memory and return the polymer to its non-equilibrium state. Many experimental and mathematical simulations have been conducted so far to investigate the rejuvenation of glassy polymers by applying mechanical stresses, i.e., mechanical rejuvenation. However, to turn a glassy polymer to its non-equilibrium state by imposing mechanical stress on the polymer is still under debate. Some scientists agree and others disagree with the idea. It was found that small strains can over-age an amorphous polymer, however, large strains can cause mechanical rejuvenation. In pre-yield regime, straining a polymer will not change its state and mechanical rejuvenation does not occur. In post-yield regime, straining will change the state of the system, but, it is totally different from that of an unaged sample. In this article, our aim is to present some information on physical aging and also discuss a controversial topic of thermal and mechanical rejuvenation of glassy amorphous polymers by reviewing the recently published papers.

کلیدواژه‌ها [English]

  • glassy amorphous polymer
  • physical aging
  • thermal rejuvenation
  • mechanical rejuvenation
  • memory effect

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