رزین های پلی یورتان پلی ال
رزین های پلی یورتان پلی ال (Polyurethane resin polyol) پلیمرهایی هستند که در ساختار مولکولی خود به طور معمول تعداد دو یا بیشتر گروه هیدروکسیل دارند. حجم عمده ی ماده ی اولیه در ساخت پلی یورتان ها را پلی ال ها تشکیل میدهند. کسر وزنی پلی ال مورد استفاده، وابسته به کاربرد پلی یورتان، متفاوت است؛ در بتونه های منعطف 90% وزنی، در فومهای نرم 70% وزنی و در فومهای سخت حدود 30% وزنی از پلی ال ها استفاده میشود. با توجه به مقادیر ذکر شده پلی ال ها در پلی یورتان باعث ایجاد نرمی و انعطاف پذیری میشود و در مقابل، ایزوسیانات ها و کمک واکنش دهنده ها باعث سخت و چغرمه شدن پلی یورتان ها می شوند.
رزین های پلی ال با توجه به ساختار موکلکولی انواع مختلفی دارند. بیشترین رزین پلی یورتان پلی ال ای مورد استفاده در صنعت دارای پیوندهای استری و یا اتری هستند. پلی ال های دیگر دارای ساختار های کربناتی، آکریلیکی و اتری گرفته شده از THF (تتراهیدروفوران) می باشد. این پلی ال ها به علت قیمت بالاترشان کاربردهای محدودتری در صنعت دارد.
پلی اتر پلی ال ها :
پلی یورتان حاصله از پلی اتر پلی ال های (Polyether polyol) برپایه ی پروپیلن اکساید و پلی اتیلن اکساید ویسکوزیته ی پایین و انعطاف پذیری مناسبی داشته و مقاومت بالایی در برابر هیدرولیز از خود نشان می دهند. قیمت پایین نیز یکی دیگر از مزایای این پلی ال هاست. درمقابل، مقاومت پایین در برابر اکسید شدن، مقاومت پایین در برابر حرارت، مقاومت های پایین مکانیکی و آتش زا بودن این مواد، از جمله معایب این دسته از پلی ال ها به شمار می روند. پلی یورتان حاصله از پلی اتر پلی ال های برپایه ی تتراهیدروفوران مقاومت مکانیکی خوبی از خود نشان می دهند اما ویسکوزیته و قیمت بالای آن ها جزو معایب آنهاست.
پلی استر پلیالها:
پلی یورتان های حاصله از پلی استر پلی ال های (polyester polyol) آلیفاتیک مقاومت به اکسید شدن خوبی داشته و خواص مکانیکی خوبی از خود نشان میدهد اما این مواد ویسکوزیته ی بالایی داشته و مقاومت پایینی در برابر هیدرولیز دارند. از طرفی پلی یورتان های حاصله از پلی استر پلی ال های آروماتیک سختی بالاتری داشته مقاومت به شعله از خود نشان میدهد.
آکریلیک پلی ال ها:
رزین پلی یورتان های حاصله از آکریلیک پلی ال ها polyurethane acrylic polyol resin مقاومت به هیدرولیز و اکسید شدن خوب و سختی بالایی دارد اما قیمت و ویسکوزیته ی بالا و انعطاف پذیری پایین آنها از جمله معایب آنهاست. در بخش رزین های پلی یورتان اکریلیک پلی ال به طول کامل به این دسته پرداخته شده است.
پلی کربنات پلی ال:
پلی یورتان های حاصله از پلی کربنات پلی ال ها polyurethane polycarbonate polyol resin مقاومت به هیدرولیز و اکسید شدن و خواص مکانیکی بالایی دارمد اما ویسکوزیته و قیمت بالا از معایب این پلی یورتان ها به شمار میآید.
پلی بوتادین پلی ال:
پلی یورتان های حاصله از پلی بوتادین پلی ال ها انعطاف پذیری و مقاومت شیمیایی خوبی دارند اما مقاومت حرارتی آن ها پایین بوده و ویسکوزیته و قیمت بالایی نیز دارند.
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