Ekstrüzyon şişirme kalıplama uygulamaları için yüksek yoğunluklu polietilen kompozit malzeme geliştirilmesi ve karakterizasyonu
Development and characterization of high density polyethylene composite materials for extrusion blow molding applications
Yazar: LEYLA YANMAZ
Danışman: PROF. DR. FATMA SENİHA GÜNER
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2016
Konu: Kimya Mühendisliği = Chemical Engineering ; Polimer Bilim ve Teknolojisi = Polymer Science and Technology

Özet:
Polimer kompozit malzemeler uzun yıllardır çalışılmaktadır ve son yıllarda bu konuda büyük mesafeler kat edilmiştir. Polimer matrisli kompozit malzemeler gelişmiş mekanik, bariyer ve termal özelliklerinden dolayı otomobil, uzay, inşaat ve ambalaj endüstrisi gibi birçok sektörde tercih edilmektedir. 
Dünyada en çok kullanım alanına sahip polimerlerden biri olan yüksek yoğunluklu polietilenin (YYPE) darbe dayanımı, akma-çekme dayanımları, aşınma direnci, elektrik yalıtım özellikleri, gaz geçirgenliği gibi özelliklerini geliştirmek amacıyla mika, talk, cam elyaf, kil, kalsiyum karbonat (CaCO3), grafit gibi malzemeler takviye malzemesi olarak kullanılmaktadır. 
Bu çalışmada ekstrüzyon şişirme kalıplama uygulamalarında kullanılmak üzere yüksek yoğunluklu polietilen kompozitler hazırlanarak karakterizasyonları yapılmıştır. YYPE'nin mekanik özelliklerini geliştirmek amacıyla organik olarak modifiye edilmiş montmorillonit (OMMT) kil, CaCO3 ve cam elyaf kullanılmıştır. 
Takviye malzemelerinin polimer matrisiyle uyumluluğu kompozit malzemenin mekanik özelliklerini etkileyen en önemli faktördür. Bu uyumluluğu arttırmak için genellikle maleik anhidrat aşılanmış poliolefinler kullanılmaktadır. Dolayısıyla kil ve CaCO3'ün polimer matrisiyle daha uyumlu hale gelerek matris içerisinde homojen olarak dağılmasını sağlamak için uyumlaştırıcı olarak maleik anhidrat aşılanmış yüksek yoğunluklu polietilen (PEgMA) kullanılmıştır. Cam elyaf katkılı kompozitlerin hazırlanmasında uyumlaştırıcı kullanılmamıştır.
Uyumlaştırıcı içeren ve içermeyen kompozit malzemeler ekstrüzyon şişirme kalıplama yöntemi ile üretilerek malzemelerin karakterizasyonları yapılmıştır. Kompozit malzemelerin karakterizasyonları için Fourier dönüşümlü infrared spektroskopisi (FTIR) ve diferansiyel taramalı kalorimetre (DSC) cihazları kullanılmış, ayrıca ısıl gravimetrik analiz (TGA), çekme testi, basma testi ve reolojik testler gerçekleştirilmiştir.
Uyumlaştırıcı içeren ve içermeyen kompozit malzemeler için %1 ve %4 oranlarında kil, %15 oranında CaCO3, %1 ve %2 oranlarında cam elyaf kullanılmıştır. Uyumlaştırıcı ve kil içeren malzemeler için uyumlaştırıcı/kil oranı 3:1 olacak şekilde PEgMA, CaCO3 için ise %2 oranında PEgMA kullanılmıştır. 
Yapılan FTIR analizinde takviye malzemelerinin YYPE matrisi ile etkileşmediği belirlenmiştir. Isıl analizde de takviye malzemelerinin kompozitin erime sıcaklığına belirgin bir etkisi olmadığı tespit edilmiştir. Ayrıca takviye malzemelerinin kompozitlerin akış özelliğini prosesi etkileyecek şekilde değiştirmediği sonucu çıkarılmıştır. %2 cam elyaf takviyesinin YYPE'nin mekanik özelliklerini geliştirdiği görülmüştür. Kil ve CaCO3 takviyesi ise YYPE'nin mekanik özelliklerini düşürmüştür.

Abstract:
Polymer composite materials have been studied for a long time and in the recent years there are extensive developments in this field. Composites based on polymer matrix are favored in many industrial applications due to their enhanced mechanical, barrier and thermal properties. 
High density polyethylene (HDPE) is one of the most popular and widely used polymer in the world especially in the packaging industry.  Reinforcement materials including clay, glass fibers, talc, mica, calcium carbonate (CaCO3) are added into polymer to achieve better material properties. 
Final properties of composites depend on the dispersion and orientation of reinforcement materials  in HDPE matrix, which is determined by filler structure, surface area and chemical activity. Besides, physico-chemical properties of matrix and reinforcement material, the composite composition and preparation method determine the final properties of the composite.  These properties are directly related to interfacial interactions between polymer matrix and reinforcement materials. If reinforcement materials cannot adsorb to polymer matrix, they tend to agglomerate, and hence decreasing mechanical properties. 
Due to nonpolar properties of polyethylene, proper dispersion of clay and CaCO3 cannot be achieved. Therefore, modified polar compatibilizers such as maleic anhydrate grafted polyethylene (PEgMA) can be used to enhance compatibility between  reinforcement material and polyethylene. In addition, surface treatment can be performed for calcium carbonate to improve dispersion and compatibility with polymer matrix. 
The aim of this study is developing and characterizing HDPE composites that will be used in extrusion blow molding applications. Organically modified montmorillonite clay (OMMT), calcium carbonate treated with stearic acid and glass fiber with diameter of 10 µm and length of 4.5 mm were used as reinforcement materials for HDPE in this study. 
Since it is economic, environmentally friendly and easier, masterbatches containing high concentrations of reinforcement materials was used and diluted by neat HDPE to obtain desired loading of reinforcement materials. PEgMA was used as compatibilizer to enhance interfacial interactions between clay and HDPE and CaCO3 and HDPE. HDPE composites with and without compatibilizer were prepared in single screw extruder and molded with extrusion blow molding process. 
Fourier transform infrared spectrescopy (FTIR), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), tensile test, top load test and reological analysis were carried out for characterization of composites. 

The amounts of clay in the composites were 1 and 4 wt% of HDPE, the amount of CaCO3 was 15 wt% of HDPE and the amount of glass fiber was 1 and 2 wt% of HDPE. Compatibilizer/clay ratio was 3:1 for clay-HDPE composites and compatibilizer amount for CaCO3-HDPE composite was 2 wt%.
HDPE and reinforcement materials were hand mixed prior to fed into extruder. A single screw extruder having diameter of 80 mm, L/D ratio of 24 and rotating speed of 62 cycle/min. was used for compounding of materials. The operation temperature range of the extruder was 175˚C to 185˚C. Compounded materials were extrusion blow molded with blowing temperature of 190˚C and blowing pressure of 7 bar. 
FTIR analysis within the spectrum range of 4000 to 650 cm-1 was performed for structural characterization of composites. Characteristic stretching peaks of HDPE between 2950 and 2850 cm-1, bending peaks of 1472 and 1462 cm-1, rocking deformation peaks between 731 and 720 cm-1 were observed. It was seen that addition of reinforcement materials did not alter the shape or position of the HDPE peaks. 
DSC analysis was performed to observe melting point (Tm) and enthalpy change (ΔH) of composites. Reinforcement materials did not affect the melting points prominently compared to neat HDPE. There is a little change (±1 or 2˚C) for some of the samples. Since high temperatures are used in the processing of composite materials, this changes can be ignored. Crystallinity of composites were calculated using enthalpy changes and it was observed that clay and calcium carbonate addition decreased the crystallinity degree, however glass fiber and compatibilizer-clay addition  increased the crystallinity.  
Composition of composite materials were determined with TGA. Expected compositions of reinforcement materials could not be achieved due to sticking of materials to the hopper or other extruder parts. In addition, ineffective mixing of HDPE and reinforcement materials could be another reason.
The reological properties of composites were measured with rotational rheometer for low shear rates and capillary rheometer for high shear rates. Rotational rheometer analysis was performed between 0.1 to 0.15 s-1 at 170˚C and 200˚C. There is no significant change in shear stress and viscosity of composites that was produced without compatibilizer at 170˚C. Shear stress and viscosity of 4 wt% clay-HDPE composite that was produced with compatibilizer decreased compared to neat HDPE and other composites. However, capillary rheometry results show that there is no change in viscosity of 4 wt% clay-HDPE composite at high shear rates that was produced with compatibilizer. Since the composite preparation occurs at high shear rates, that decrease in low shear rates can be ignored.
Tensile and top load tests were performed to determine mechanical properties of composites. Yield strength of all composites except 2 wt% glass fiber-HDPE composite decreased. However, addition of compatibilizer increased yield strengths when compared to composites that were produced without compatibilizer.
The reason of decrease in mechanical properties for other composites could be due to poor adhesion between reinforcement materials and HDPE matrix. Since dispersion of the reinforcement material is the most important parameter for mechanical properties of composite, it was thought that clay and calcium carbonate did not disperse adequately and they agglomerated. 
Consequently, it can be concluded that mechanical properties of HDPE that was extrusion blow molded can be enhanced with addition of 2 wt% glass fiber.