The effect of lignocellulosic filler types and concentrations on the mechanical properties of wood plastic composites produced with polypropylene having various melt flowing index (MFI) Farklı erime akış indeksine sahip polipropilenlerle üretilen odun plastik kompozitlerin mekanik özellikleri üz

Öz In this study, the types and loading of lignocellulosic fillers on the properties of different melt flow index (MFI) polypropylene (PP) based wood plastic composites (WPCs) were determined. Olive pirinas and wood flour (Pinusbrutia Ten.) were used as lignocellulosic fillers at the loading rate of 20% and 40%. Composites were produced by mixing wood flour or pirinas, wax, maleic anhydride grafted polypropylene (MAPP) and low or high MFI PP in a high intensity density mixer. The homogenous mixture was extruded using a single screw extruder with five heating zones. Extrudates were pelletized and composite specimens were injection molded. Control specimens were produced without adding any filler. The physical and mechanical and thermal properties were determined. It is stated that there is no effect of the melt flow index on the some properties of wood plastic composite, however; the mechanical properties compensates the values stated as in ASTM D 6662 standards even though it varies according to the types and rates of the fillers. Bu çalışmada, lignoselülozik dolgu maddesi türü, kullanım oranı ve erime akış indeksinin odun plastik kompozitlerin (OPK) özelliklerine etkisinin belirlenmesi hedeflenmiştir. Lignoselülozik dolgu maddesi olarak zeytin pirinası ve kızılçam odun unu %20 ve %40 oranlarında kullanılmıştır. Kızılçam odun unu veya zeytin pirinası, vaks ve maleik anhidrit graftlanmış polipropilen (MAPP)ve yüksek veya düşük erime akış indeksine sahip polipropilen üretim reçetesine göre yüksek devirli mikser yardımıyla homojen bir şekilde karıştırılmıştır. Homojen karışım öncelikle tek vidalı eksturuder de karıştırılarak odun plastik kompozit karışımları oluşturulmuş ve bu karışımlar kırıcı yardımıyla pelletler haline dönüştürülmüştür. Üretilen pelletler kullanılarak enjeksiyon kalıplama makinesinde deney numuneleri üretilmiştir. Kontrol numuneleri dolgu maddesi katılmadan üretimler gerçekleştirilmiştir. Üretilen deney numunelerinin fiziksel ve mekanik özellikleri belirlenmiştir. Erime akış indeksinin OPK'lerin özelliklerine önemli bir etkisinin olmadığı buna karşın dolgu maddesi türü ve oranına göre değişkenlik göstermesine rağmen mekanik özelliklerin ASTM D 6662 standardında belirlenen değerleri karşıladığı tespit edilmiştir.


Introduction
Wood-plastic composites (WPCs) are materials that combine wood and polymer in a certain matrix. The WPCs consist of thewood flour, polymer and additives in different amounts. The manufacturing of these are quite similar with the manufacturing process and techniques thermoplastic polymers. The WPCs have been used highly in many areas, applications and industries since the 1990s [1]. As the population grows, the need of alternative raw materials is rising. The procedure of recycling waste lignocellulosic materials decreases the need of raw materials. Manufacturing the WPCs lignocellulosic materials are used as filler [2]. Wood flour and plastic matrix constitute the main ingredients in WPC formulations. The amounts of wood flour vary in the formulations and wood flour content of up to 70% is currently used in commercial WPC products. The amount of wood flour in WPCs significantly influences bothprocessing and end-use properties. The type of wood species constitutes another important factor to consider in WPCs [3].
The Turkish red pine (Pinus brutia Ten.) is naturally grown in Turkey, especially in the sea side regions of the Mediterneaen, the Aegean and the Marmara region [4]. Turkish red pine (Pinusbrutia Ten.), wood has been used in the paper and cellulosic industries, construction material, packing case, agricultural tools, wooden wire poles, mine poles, fence, tools and cases and also in the construction of marine vehicles [5], [6]. As the amount of the residue of Turkish red pine wood varies according to being cut saw machine or a gang saw, a log is 60% efficient [7]. In other words 40% of a logs are residue.
Olive trees are spread between lattitudes of 30 and 45 degrees of northern and southern hemisphere, especially having Mediterranean climate conditions, over the five continents of the world [8]. Turkey, situated in Mediterranean Basin is one of the most important olive and olive oil producers in the  [9]. Pirina which will be produced out of the olives and while of amount pirina and oil which is produced out of olives change according to the production technique, the type of the olives and the oil processing, 35-45 kg of pirina and 15-22 kg of olive oil is produced out of approximately 100 kg of olives [10].
The amount of residue pirina in the oil industry of Turkey is approximately 200.000 tons. Pirina, which is not well evaluated commercially is used as fuel, it is also purchased by distributes or is dumped to the wasteland. This is also causes environmental pollution [11].
The purpose of this work is to study the effect of concentration and type of lignocellulosic fillers on the mechanical properties of polypropylene based WPCs. Turkish red pine flour (RPF) and olive pirinas (OF) was used as lignocellulosic materials and high and low melt flow index polypropylene was utilized as polymeric matrices. Some mechanical properties such as tensile strength, flexural strength, impact strength and linear burning rate of WPCs were evaluated.

Materials
In this study; lignocellulosic fillers Turkish red pine flour (RPF)and olive pirinas(OP) were used. Turkish red pine particles were supplied by wood working atelier and olive pirinas supplied from olive oil mill in Kahramanmaraş city. High and low melt flow index Polypropylenes (MH 418 and EH 241) used in the experiments was obtained from Petkim Petrochemical Co. in Turkey. Some mechanical, physical and thermal properties of Polypropylene were shown in Table1. For coupling agents; maleic anhydrite grafted polypropylene (MAPP) (Licomont AR 504 supplied from Clariant) and for lubricant paraffin wax (K.130.1000)were added of weight of 3% to improve the performances of WPCs. Some properties of coupling agent and wax were given in Table 2.

Composite manufacturing
The lignocellulosic fillers RPF and OP were turned into flour form with using a Wiley mill. These flours were classifiedin 20-40-60-80-100 to 200 mesh-sizes. Classified particles ( Figure 1) which passed by a 40 mesh and which were remain on 60 mesh (0.25 mmor 250 micron) were used. The 60 mesh Turkish red pine flour (RPF) and olive pirinas flour (OP) were dessicated in oven for 24 hours at 103 °C (±2). The moisture content of dried filler materials was below 1%. Using the formulation; lignocellulosic fillers, polypropylene (PP) with high and low melt flow index, lubricant and maleic anhydrite grafted polypropylene were mixed in a mixer (900-1000 rpm in 2 sec.) to produce for homogeneous blend.
The manufacturing schedule of the study was given Table 3.
Stabilizing the rates of MAPP and wax in this mixture, pirinas and wood flour were added with the rates of 20% and 40%. Wax and MAPP were added only into control test specimens without any filler materials.  By using a single-screw extruder at 40 rpm screw speed in the temperatures (from barrel to die) of 170-180-185-190-200°C respectively these blends were compounded. Extruded specimens were cooled in water pool (23 °C ±2 ) and then pelletized into pellets form with grinding machine. The pellets were dessicated in oven at 103 °C (±2) for 24 hours. The moisture content of dried wood plastic pellets was below 1% before the injection molding.The injection molding machine (HAIDA HDX-88) was used for manufacture test specimens. The temperatures of injection molding machine were 180-190-200°C (from feed zone to die zone). The injection pressure, speed and cooling speed were 5-6 MPa, 80 mm/Sec. and 30sec. respectively.

Composites testing
All test specimens were tested in a climate-controlled testing laboratory. Depending on the ASTM D 635 standart, horizontal burning test (Figure 2) was performed. The dimensions of specimens were 4 X13X125 mm. The average burning rate was determined as to the mark in mm/min. Ten specimens were burned for each group. Atlas HVUL2 horizontal vertical flame chamber test machine was used in this study.

Results and discussion
In this study, the effect of melt flow index (MFI) of PP, filler type and filler rate on the some properties of WPCs were studied. Density, flexural (flexural strength, flexural modulus), tensile (tensile strength, tensile modulus, elongation at break), impact, hardness and burning rate properties were determined.
All manufactured WPCs were in the density range of 0.89 and 1.04 g/cm 3 . The interaction charts of the density were presented in Figure 3. Composites manufactured with H-MFI and L-MFI was presented in Figure 3A and 3B, respectively. Statistical analysis showed that MFI of PP was not significantly important for density. Both H-MFI and L-MFI composites provided similar densities (P=0.1736). Both Filler type and filler rate, had a significant effect on density (P=0.0033 and P<0.0001). Both filler increased density. This increase was due to the higher cell wall density of lignocellulosic Materials [13], [14]. Between RPF and OP fillers, RPF provided higher density values than OP filler.
Flexural strength values ranged from 29.38 and 46.16MPa. The interaction charts of the flexural properties were presented in Figure 4.  [15], [16].
This resulted in improved flexural modulus values compared to unfilled ones. Therefore, flexural modulus increased with the rise of lignocellulosic filler loading [2].    [17].
At the point of elongation at break valueswere in the range of 3.90% and 455.23% and MFI type had significant effecton them (P<0.0001). L-MFI has higher elongation at break values compared to H-MFI. It should be noted that when the lignocellulosic filler was added into polymer matrix elongation at break levels were significantly scaled down. Even 20% filler addition had reduced pure L-MFI specimens' elongation at break values from 450% to 7%. Polymercomposites became stiffer when the amount of filler in the matrix was increased. So, the elongation at break values was decreased. L-MFI index provided slightly higher results than H-MFI ones.
In addition RPF filled composites provided increased hardness values than OP filled ones. The hardness of the test specimens were increased depend on filler types and filler rate [19]. The charts of burning rate values was given in Figure 8. The mean values were ranged for the burning rate from 16.52 to 35.90 mm\min. These values were calculated by measuring the burned distance per minute. The highest burning rate means it burns faster. It was interesting to see that composites utilizing H-MFI matrix had the lowest burning rate when it was filled with OP. Oppositely, RPF filled composites provided lowest burning rate when L-MFI polymeric matrix was used. This can be related with heat capacity of the polymer, wood flour [20] and olive pirinas flour. There is a need for follow up studies to understand this behaviour.

Conclusions
Wood plastic composites with different melt flow index were measured and effect of filler type and filler rate on selected properties were evaluated. For the tensile strength and tensile modulus, melt flow index of the polymer did not have significant effect. If lignocellulosic filler present in the formulation, melt flow index also was not important. Regardless of MFI, filler rate and type had a significant effect on studied properties. RPF filled composites outperformed the OP filled ones. However, both fillers met the sufficient mechanical properties of ASTM D 6662. RPF and OP flour fillers from waste materials can be utilized in composite manufacturing.