Polipropilenin darbe mukavemeti üzerine kalsiyum karnonat ve tavlamanın etkisi

Abstract

Bu çalışmada ; polipropilen plastik malzemeleri ile ilgili yapısal, fiziksel, kimyasal özelliklerle imalat ve kullanım alanlarında bilgiler verilmiştir. Isıl işlemin ve CaC03 'in, enjeksiyonluk, ağırlıkça %10 ve %20 CaC03 katkılı olmak üzere üç tip homopolimer polipropilenin darbe mukavemeti üzerine etkisi incelendi. 115 ve 125 °C 'de 1,4,6 ve 15 saat tavlanan numunelerin darbe dayanımı oda sıcaklığında test edildi. Tavlanmamış numunelerle oda sıcaklığında yapılan deneylerde CaC03 'm polipropilenin darbe dayanımını arttırdığı gözlendi. Bu artış %10 CaC03 katkılı polipropilende %20 katkılı polipropilene nazaran daha fazlaydı. CaC03 'm polipropilenin darbe mukavemetini arttırması CaC03 dolgusu ve polipropilen matris arasında oluşan ara faza ve malzemenin kristalinite derecesinin düşmesine bağlanmıştır. Tavlanmış numunelerle oda sıcaklığında yapılan deneylerde enjeksiyonluk polipropilenin darbe dayanımı tavlama sıcaklığına ve belli bir tavlama süresine bağlı olarak azaldı. %10 CaC03 katkılı polipropilenin darbe mukavemeti ise enjeksiyonluk polipropilene göre ters bir davranış sergileyerek tavlama sıcaklığı ve belli bir tavlama süresine bağlı olarak arttı. %20 CaC03 katkılı polipropilenin darbe dayanımı ise tavlama sıcaklığı ve süresinden etkilenmedi. Enjeksiyonluk polipropilenin darbe mukavemetindeki bu düşüş malzemenin kristalinite derecesinin artmasına, %10 CaC03 katkılı polipropilenin darbe dayanımındaki artış ise oluşan arafazın kalınlığının tavlama ile birlikte artmasına bağlı olarak izah edilmeye çalışılmıştır.

Effect of Annealing and Calcium Carbonate Filler on the Impact Strenght of Polypropylene. Plastics are relatively large volume structural materials comparable in importance to metals. Wide spread use and rapid growth of plastics in the recent fifty years result largely from cheapness, lightness, processibility and high chemical resistance that they have. Mechanical propeties can be improved especially when they are alloyed with other plastics or materials. Polypropylene is a homopolymer of proyplene whose sales have grown over the years to become one of the largest engineering thermoplastic in the world. Polypropylene is manufactured by the polymerization of high-purity propylene, using Natta-Ziegler catalysts that connects the monomer units head-to-tail with very high reliability. Polypropylene molecules can be divided into three groups according to their stereospecificity. 1. Atactic polypropylene where methyl groups in the chain are specially arranged. in an irregular, completely random manner. 2. Snydytactic polypropylene where the structure is spatially ordered methyl groups all occur one side of the main hydrocarbon chain. 3. Izotactic polypropylene where the methyl groups alternate from side to side of the plane of the carbon chain. Polypropylene is a partially crystalline plastic so it contains amourphous and crysttalline parts. Amourphous parts increase the impact strength of polymer owing to their mobility. Typical samples of commercial polypropylene must contain 93% isotactic molecules. Polypropylene has a number desirable properties that make it a versalite material among modern termoplastic polymers. It exhibits vui high yield strength, high heat distortion temparature and good surface hardness. It is essentially unaffected by most chemicals at or near ambient temparature and does not stress crack. The poor impact strenght and some mechanical properties of polypropylene can be improved by controlling its moleculer weight. Polypropylene with high moleculer weight exhibits better impact strenght, resistance to creep, surface hardness and brittle point. The properties of polypropylene resins may be broadened with more monomers during polymerization or by blending with other plastics. A useful feature of polypropylene resin is its ability to be alloyed with variety of polymers. Most common alloys are PP/PE alloys which have improved impact strength and brittle temparature than polypropylene homopolymer. However, the disadvantage of these alloys is to exhibit poor tensile strength. Some fillers can be blended into polypropylene polymers to prevent degradation during processing and increase productivity and some mechanical properties. The most common additives that are used for filling are talk, calcium carbonate (CaC03) glass fiber and magnesium hidroxide (MgOH2). Polypropylene is highly resistant to chemicals. It dissolves in high boiling aliphatic and aromatic hydrocarbons at high temparatures. It is attacted by oxidizing agents, such as sulfuric acids and nitric acid Polypropylene, containing bonded hydrogen atoms and terriary carbon atoms in its chain, reacts with oxygen in several ways, causing the chain to break and the polymer become brittle. This action is promoted by high temparatures, light or mechanical stress. Stabilizers are added for protection. Polypropylene is a typical thermoplastic whose flow behavior is above the melting point. A large variety of processing options are available, including injection moulding, extrusion and blow moulding. injection pressures of polypropylene are between 45 and 105 MPa and typical clamping forces are 28-35 MPa. Polypropylene is sensitive to failure at notches so smooth radius are recommended at all sharp angles and corners in injection moulding. Polypropylene is extruded into sheet stamping and also into pipes and profiles. High moleculer weight, low melt flow materials used in extrusion moulding. Extruders with length-diameter ratios ( 24 : 1 or 30 : 1) provide the required melt strength. Low melt IX flow copolymers are used in blow moulding for hot fill and have good contact clarity. Polypropylene has various excellent properties as a general purpose resin, such as thermal resistance rigidity and chemical resistance. However, its greatest disadvantage is its low impact strength. In many of previous studies this property of polypropylene was investigated. In this study effect of annealing and CaC03 filler on the impact strength of polypropylene was investigated. For this purpose three grades of polypropylene were selected. Polypropylene resins used were homopolymer polypropylene for injection moulding (Novolen 1100 N made by Basf), 10wt% CaC03 -filled polypropylene (MNF 10 made by Teknopolimer) and 20wt% CaC03 -filled polypropylene (MNF 20 made by Teknopolimer). MNF 10 and MNF 20 polypropylenes were produced by adding CaC03 into Navolen 1100N on an extruder with two-roll mill at 190 °C. The injection moulded specimens were prepared at a softening temparature about 220 °C. The dimensions of the specimens were 130 mm length, 12,7 mm width and 3,43 mm thickness. All specimens were centerally single edge notched. The depth of the notch was 2,54 mm with an angle of 45 ° and radius of 0,25 mm. The impact strength of the specimens were tested with a ceast 6545/000 pendulum impact tester by Charpy impact test method according to ASTM-D256. For all specimens 1 joule hammer were used. Melt flow index was measured at 230 °C under a 2,16 kg load according to ASTM-D1238 by a ceast S.P.A. Turin I. equipment. The three grades of polypropylene were annealed at 115 °C and 125 °C for 1 hour, 4 hours, 6 hours and 15 hours.By that heat treatment each polypropylene grade had eight annealed and one unannealed kinds of specimens. The specimens were tested at room temparature. From each annealed and unannealed kinds of specimens 5 or 7 specimens were tested to have the average impact energy. Impact strength values were shown versus annealing time and annealing temparatures in figures. In general, impact strengths of 10 and 20 % CaC03 filled polypropylene was 1,55 and 1,1 times higher respectively than impact strength of polypropylene for injection moulding when it was measured at room temparature. From these results, it can be seen that CaC03 filler has a significant effect on impact strength of polypropylene. Impact strength of polypropylene for injection moulding decreased by annealing untill the equilibrium state. The impact strength of the specimens annealed at 125 °C decreased more sharply in comparison with the specimens annealed at 115 °C. Impact strength reached the equilibrium state in 4 hours by annealing at each temparature of 115 °C and 125 °C. 10% CaC03 filled polypropylene has the highest impact strength among these three grades of polyproylene. In contrast to decrease in impact strength of polypropylene for injection moulding by annealing, annealing of 10% CaC03 filled polypropylene improved impact strength. Impact strength was saturated in 4 hours of annealing like polypropylene for injection moulding and the specimens annealed at 125 °C had higher strength than ones annealed at 115 °C. The specimens annealed at 125 °C for 4 hours showed about 19% impact strength increase in comparison with the ones unannealed. It can be shown from figure 4.2 that impact strength values of 20% CaC03 filled polypropylene incomparison with 10% CaC03 filled polypropylene maybe ascribed the agglomeration tendency of the CaC03 particles. Added to this, in CaC03 filled polypropylene an interphase layer is formed between the filler surface and polymer matrix by the adsorption of amorphous polymer chains to the filler surface. Impact strength of CaC03 filled polypropylene recovers due to forming the interphase. The increase in impact strength of CaC03 filled polypropylene is depedent of the thickness volume of interphase and the dispersity of CaC03 filler. The higher the dispersity and the greater volume or thickness of interphase means the increased impact strength. Because of these, impact strength of 10% CaC03 filled polypropylene has greater than 20% CaC03 filled polypropylene. Annealing decreased impact strength of polypropylene for injection moulding and its effect was significant at higher annealing temparature. The fracture mechanism of polypropylene for injection moulding is closely related to crystallinity and lamella thickness. Recrystallization, migration of amorphous polypropylene and increase of lamella thickness occur in the crystalline areas of polypropylene for injection moulding within 4 hours by annealing. Recrystallization and enhancement of lamella thickness increase XI hardness brittleness of polypropylene but migration of amorphous polypropylene contributes to a decrease in brittle temparature (Tb) 10% CaC03 filled polypropylene showed an increase in its impact strength by annealing in contrast to polypropylene for injection moulding. This increase can be attributed to morphological changes in the continous polypropylene phase and interphase between polymer matrix and CaC03 filler. The migration of amorphous polypropylene segments from the crystallizing part of polypropylene during annealing will increase the thickness of interphase between polymer matrix and CaC03 filler. Transfer of Amorphous Segments directs to the CaC03 filler surface where cohesion energy becomes greater than the adhesion energy. Annealing had no effect on impact strength of 20% CaC03 filled polypropylene since the thickness and the amount of volume of interphase between polymer matrix and filler are small. xu 6 7 8 9 K) Annealing Time (hour) 14 15 Figure S-l Effect of annealing time and temparature on the impact strength of PP for injection moulding. (---). Annealed at 1 15 °C, ( ) : Annealed at 125 °C. 1 2 3 4 5 6 7 8 9 10 11 12 13 U 15 Annealing Time (hour) Figure S-2.Effect of annealing time and tempature on impact strength of %20 CaCO. filled PP. (---): Annealed at 115 °C ( ) : Annealed at 125 °C. xni 5 -.0 e 00 o 03 s O 6 7 8 9 10 Annealing Time (hour) 11 13 15 Figure S-3.Effect of annealing time and temparature on impact strength of %10 CaC03 filled PP. (- - - ) : annealed at 115 °C, ( ) : annealed at 125 °C. XIV 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Annealing Time (hour) Figure S-4. Effect of annealing at 115°C and annealing time on the impact strength of polypropylene. ( ) : 10 % CaC03 filled PP, (-..-..-..) : 20 % CaCO- filled PP,(- - - ) : PP for injection moulding.