Mineral dolguların polipropilen/ elastomer kompozitlerine etkileri

Abstract

MİNERAL DOLGULARIN POLİPROPİLEN/ ELASTOMER KOMPOZİTLERİNE ETKİLERİ İzotaktik polipropilen yarı kristalin yapısı ve çok değişik özellikleri nedeniyle yaygın olarak kullanılan bir termoplastiktir. Buna rağmen basit molekül yapısına sahiptir. Yapısı ve özellikleri kristalin miktarına, amorf ve kristalin bölgelerin miktarına,kristal boyutlarına, kalıplama şartlarına, kimyasal özelliklerine, dolgu, katkı ve takviyelendiricilerin miktarına bağlıdır. Polipropilen özellikle düşük sıcaklıklarda düşük darbe mukavemetine sahiptir. Bundan dolayı sadece fiyat ve performans açısından değil düşük servis şartlarında dayanım özellikleri nedeniyle elastomerler ve değişik maddelerle takviyelendirilerek tokluk özellikleri yükseltilebilmektedir. Bu tez çalışmasında kalsiyum karbonat ve talk mineral dolguların polipropilen/ elastomer (etilen vinil asetat) kompozitlerinin mekanik, morfolojik ve termal özellikleri araştırıldı. Mineral dolguların özelliklere etkilerinin yanında ısıl işlemin özellikler üzerindeki etkileri araştırıldı. Bu amaçla % 0, 3, 6, 9, 12 ve oranında mineral dolgu maddeleri yukarıda da ifade edildiği gibi kalsiyum karbonat ve talk 88/ 12 oranındaki polipropilen/ etilen vinil asetat matris malzemesine karıştırıldı. Üretilen karışım kompozitlerin akma, çekme, elastisite modülü, çentikli izod darbe mukavemeti (çentik yarıçapı 0.25 mm ve 1) sertlik, akışkanlık (MFI), ısıl sıcaklıkları ve morfolojik özellikleri incelendi. Isıl işlemin etkilerini incelemek için numuneler 100 oC de 75, 100 ve 150 saat ısıl işleme maruz bırakıldı. Elde edilen verilerden polipropilen/ elastomer kompozitlerinin özelliklerinin mineral dolgu maddelerinin yapı içindeki oranına bağlı olarak değiştiği tespit edildi. Özellikle mineral dolgular çekme mukavemetlerini düşürürken uzama ve elastiklik modüllerinin ve darbe mukavemetlerini yükselttiği belirlendi. Özellikle elastiklik modüllerinde % 3'lük mineral dolgu maddesi ile önemli bir artış gösterdiği saptandı. Darbe mukavemetleri incelendiğinde çentik yarı çapı 1 mm olan numunelerin % 3'lük mineral dolgu maddeleri ile elde edildiği daha yüksek oranlarda azaltıcı etki yaptığı deneysel çalışmalardan görüldü. Ancak 100 oC ısıl işlem sıcaklığı ve 100 saatlik ısıl işlem zamanının özellikler üzerinde 75 ve 150 saatten daha etkili olduğu saptandı. Mineral dolgu maddelerinin artışının homojen dağılım üzerinde olumsuz etki ettiği bunun morfolojik sonuçlarla desteklendi buna karşın % 15'lik mineral dolgu maddesi miktarının Tm sıcaklığını yaklaşık 10 oC yükselttiği belirlendi ve bu kapsamda değerlendirmeler yapıldı. Kasım 2004 Ali TAVLI

EFFECT OF MINERAL FILLERS ON THE PROPERTIES OF POLYPROPYLENE/ ELASTOMER COMPOSITES In the present study, the effect of CaCO3 and talc on the mechanical properties with heat treatment and thermal properties of the polypropylene and ethylene vinyl acetate i-PP/ EVA blends was investigated. Five different mineral filler concentrations: 3, 6, 9, 12 and 15 wt-%, were added to i-PP / EVA (88/ 12) to produce ternary composites tested. The mechanical properties such as yield and tensile strengths, elasticity modulus, Izod impact strength for notch radius of 0.25 and 1 mm, hardness with and without annealing heat treatment, and thermal properties such as melting point and melt flow index (MFI), of the composites have been investigated. The annealing heat treatment was carried out at 100 oC for three different holding times: 75, 100 and 150 hours. From the results, attempts were made to establish a relationship between mineral fillers content, annealing holding time, mechanical and thermal properties to obtain best results. From the tensile test results it was seen that heat treatment was not so effective on ultimate tensile strength and yield strength and tensile strengths decreased gradually with the increase in mineral filler content. However, mineral fillers were effective to achieve higher elasticity modulus, impact strengths and hardness values. Considerable increase in elasticity modulus was seen with a 3 % mineral filler content for a holding time of 100 h. Maximum impact strength for notch radius of the 1 mm was obtained for 3 % mineral filler with annealing for 100 h holding time while 9 % mineral filler content gave higher toughness values for the notch radius of 0.25 mm. The fracture surfaces also supported these results obtained for the Izod impact tests. Similarly, hardness values increased with the annealing heat treatment and increased mineral filler content. However, different holding times showed similar effects on the increased hardness values. The increased mineral filler content caused melting point to increasely 5 oC while melting flow index showed a sharp decrease as the mineral filler content increased to 3 %. Taking into consideration mechanical and thermal properties and annealing holding time, the mineral filler content of 3 % with annealing heat treatment for 100 h is recommended for optimum properties such of a ternary composite. Isotactic polypropylene (i-PP) is a semi-crystalline and multi-purpose thermoplastic with a wide range of characteristics such as good mechanical properties, corrosion resistance, low cost, easy processing, low density and easy design, etc. It has, however, simple molecular structure. Its structure and properties depend on the crystalline structure, the ratio of amorphous and crystalline phases, crystal size, molding conditions, chemical composition of the additives, fillers, fibers content, etc. Polypropylene has a low impact strength under low service temperatures. For this reason, not only the price/ performance characteristics but also the low service temperature characteristics could be improved generally with elastomers particularly ethylene-propylene copolymer (EPR), ethylene-propylene-diene ter polymer (EPDM), ethylene-vinyl acetate (EVA), etc. Although the toughness characteristics are improved by adding elastomer to polymeric structures, this causes a decrease in the elasticity modulus, tensile and yield strengths and an increase in elongation and impact strength properties. Because of this reason, multi-purpose fillers and reinforcements could be used to overcome this problem by ensuring better dimensional stability and rigidity. Particle-filled polypropylene compounds are widely used in many applications in the automotive, houseware, packaging, electric industries for the reduction of production cost of final products formed by injection molding. Molding of particle filled polypropylene blends is easier than molding of fiber reinforced blends counterparts. However, the material properties molded by injection molding could vary depending on various parameters such as the blend's matrix, the type of fillers and reinforcements used, surface characteristics, ratios and molding conditions. Parameters such as the crystallite size, tendency to crystallization, properties of matrix and fillers play an important role on the final product. The size of filler plays important role on produced polymer blend. If the size of the filler is very large, then the processability of the polymer into the mold, crystallization behaviour and orientation of matrix molecules becomes difficult. So negative effect on properties of produced blends are obvious. Calcium carbonate is the second most widely used mineral filler after talc. The use of calcium carbonate with a suitable hardness (Mohr hardness ~ 3) does not cause short term failures in processing machinery. Although the aim of filler is mostly to decrease costs. But some mechanical properties such as modulus, yield and tensile strengths can increase. However, it should be taken into account that toughness decreases while rigidity increases in polypropylene just as in plastics containing mineral fillers. In this study, the effect of CaCO3 content on the mechanical and thermal properties of İ-PP/ EVA blends have been investigated. For this aim, i-PP/ EVA/ CaCO3 composites containing 3,6,9,12 and 15 wt % CaCO3 have been produced and the properties of the ternary composites were investigated. Kasım 2004 Ali TAVLI