Utjecaj naknadnog očvršćivanja i slane vode na mehanička svojstva epoksidne smole ojačane lanenim vlaknima

master's thesis

• Title (english): Effect of postcuring and seawater on mechanical properties of composite flax fibers/epoxy
• Author: Dario Mlinarić
• Mentor: Tatjana Haramina (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2021-01-21, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering

Abstract

Tradicionalna ojačala koja se dodaju polimerima, poput staklenih vlakana, sve se više zamjenjuju prirodnim vlaknima. Lan, zbog svoje niske gustoće, posjeduje visoku specifičnu čvrstoću što ga čini jednim od najpoželjnijih prirodnih vlakana za izradu kompozita za lake konstrukcije. Hidrofilna priroda lana uzrok je slabih adhezijskih veza vlakana s polimernim matricama. Epoksidna smola superiorna je ostalim polimernim matricama u većini sustava vezano uz adhezijska svojstva. Može se naknadno očvrsnuti držanjem pri temperaturi blizu staklišta. Previsoka temperatura naknadnog učvršćivanja može dovesti do degradacije epoksidne smole i lanenih vlakana.
U radu su napravljene dvije kompozitne ploče od epoksidne smole ojačane biaksijalno orijentiranim prošivenim lanenim vlaknima. Jedna je držana 294 h u morskoj vodi pri sobnoj temperaturi, a druga 2 h pri temperaturi od 100 °C. Ispitan je utjecaj morske vode i povišene temperature na mehanička svojstva, a rezultati su uspoređeni sa svojstvima netretirane ploče. Nakon 294 h kompozit je upio 3% morske vode u odnosu na vlastitu masu, a modul kompozita je pao 27%, rastezna čvrstoća kompozita je pala 59%, a tvrdoća (vrijednost nakon minute mjerenja) je pala 61%. Nadalje, savojni modul elastičnosti je pao 40%, a savojna čvrstoća 48%. Nakon držanja pri 100 °C modul elastičnosti je pao 15%, rastezna čvrstoća je pala 56%, a tvrdoća 85%. Također, uočen je pad savojnog modula elastičnosti za 50% i savojne čvrstoće za 48%. Uz to, u oba slučaja došlo je do pada prividne smične međuslojne čvrstoće. Kod grijanog kompozita dogodio se pad od 31%, a kod kompozita izloženog utjecaju morske vode pad od 49%.

Abstract (english)

Natural fibres can be used as reinforcement in polymer matrix, substituting traditional ones like glass fibres. Because of its low density, flax shows high specific tensile strength which makes him suitable candidate for reinforcement in polymer composites. Hydrophilic nature of flax causes poor interfacial adhesion with polymer matrixes. Epoxy resin, mostly, has better interfacial adhesion compared to other thermosetting materials and can be post-cured at temperatures near the glass transition temperature. Post-curing temperatures higher than transition temperature can lead to matrix and fibre degradation.

In this work, two composites based on epoxy resin reinforced with flax bi-axial fibres were made. One was post-cured at temperature of 100 °C for 2 h, and second one was emerged in sea water for 294 h. Afterwards, mechanical properties of both composites were compared with untreated composite made of the same materials and in the same conditions. After 294 h composite showed 3% of mass uptake and resulted in decrease of tensile strength by 59% and elastic modulus by 27%. Furthermore, flexural strength decreased by 48%, flexural modulus decreased by 40%, and hardness decreased by 61%. Post-cured composite resulted in tensile strength lower by 56% and lower tensile modulus by 15%. Also, flexural strength decreased by 48% and flexural modulus decreased by 50%. Both composites resulted in lower interlaminar shear strength, 31% lower value for post-cured composite and 49% lower value regarding composite exposed to sea water.

• Keywords: epoksidna smola; lanena vlakna; morska voda; očvršćivanje; mehanička svojstva
• Keywords (english): epoxy resin; lax fibres; sea water; curing; mechanical properties
• Language: croatian
• URN:NBN: urn:nbn:hr:235:211759
• Study programme: Title: Mechanical Engineering; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka strojarstva (magistar/magistra inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2021-01-14 13:49:47