The Role of Mineral Fillers for Enhancing the Mechanical Properties

IJITE Vol.03 Issue - 03 , (March 2015) ISSN: 2321 –1776Impact Factor – 3.570

The Role of Mineral Fillers for Enhancing the Mechanical Properties of Recycled Plastics

Chilakala Ramakrishna

Hanil Cement, Researcher

Address: 302 Maepo-ri, Maepo-eup, Danyang-gun, Chungcheongbuk-do, 395-903, Korea

Thenepalli Thriveni

Mineral Resources Research Division, Researcher

Korea Institute of Geosciences and Mineral Resources (KIGAM)

Address: 124, Gwahagno, Yuseong gu, Daejeon-305350, South Korea.

Ahn Ji Whan*

Mineral Resources Research Division, Researcher

Korea Institute of Geosciences and Mineral Resources (KIGAM)

Address: 124, Gwahagno, Yuseong gu, Daejeon-305350, South Korea.

Abstract: Plastics consumption has been increased throughout the world incredibly in recent decades, the rapid depletion of natural resources and generating more and more plastic wastes throughout the world, it is necessary to conserve the natural resources and protect the environment. Recycling is the best treatment for plastic waste and also reduced the consumption of oil for producing new virgin plastic. In many applications, plastic polymer resins i.e. polypropylene (PP), polyvinyl chloride (PVC), Polyethylene terephthalate (PET) and High density polyethylene (HDPE) are not the ideal material for the job, and they don’t possess the dimensional stability required, but by the adding mineral fillers, they can increase the dimensional stability and stiffness of the materials. The present purpose of the study is the assessment of the advantage and disadvantage of mineral fillers (i.e. Talc, Kaolin, Clay and Calcium Carbonate). By observing the results precipitated calcium carbonate (PCC) is safety mineral fillers and also to enhance the mechanical properties of recycling plastics.

Index Terms: Recycling plastics; Calcium carbonates; PCC; fillers; polypropylene polymers.

ACKNOWLEDGEMENTS This research was supported by a grant (2013) from the Energy Technology Development

Program (2013T100100021) funded by the Ministry of Trade, Industrial and Energy of the Korean government.

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1. INTRODUCTION

Plastics are highly demanded in almost every industry including automotive, medical, construction, consumer goods, packaging, electrical and electronics. Nowadays, the plastics are used mainly to make cars more energy efficient by reducing weight, together with providing design flexibility, elasticity, toughness, corrosion resistance, breaking strength, hardness and durability. Basically plastics show good mechanical properties combined with polymers and polymer composites. It has been reported that in 2010 the global production of plastics increased to 265 million tonnes, confirming the long term trend of plastic production growth of almost 5% per year over the past 20 years (Fig. 1), while there is still room for further growth [1]. Each year, around 4% of global oil production represents the cost for the creation of plastic raw materials. An additional equivalent 4% of global oil production is required as energy to convert the plastic materials into prototype or finished products at the same time [2]. As a consequence, the question of the disposal of plastic waste generated by industry and householders has gained a growing public concern.

Fig. 1. World plastics production 1950–2010 [1]

Source: http:// www.plasticseurope.org/Document/plastics-the-facts (2011).



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http://www.plasticseurope.org/Document/plastics-the-facts%20(2011).


Plenty of toxic materials including dioxins and hydrochloric acid can be easily produced and cause huge damage to the environment if plastic waste is not managed properly [3-6]. Due to the increasing plastic wastes global wide is need to control of plastics wastes for environmental protection, Compared to landfill and incineration, recycling of plastic waste is much more acceptable and environment friendly. Recycling is not only an approach for disposing plastic waste, but also an effective way to reduce the requirement for virgin plastics production, which can contribute to saving with respect to global warming [7], and also the rapid depletion of natural resources, many organizations have realized that recycling of used products is important to achieve competitive advantage [8], plastics recycling have become one of the most important processes in manufacturing organizations which produce plastic products.

Any naturally occurring, homogeneous inorganic substance having a definite chemical composition and crystalline structure, color and hardness is known as mineral fillers, these fillers are used in semi-crystalline polymers, usually talc, clay, Kaolin and Precipitated calcium carbonate [9]. Generally, the addition of mineral fillers will have an embrittling effect on polymers and decrease the impact energy [10]. In fact most of the studies on modification of semi-crystalline polymers with rigid particles report a significant loss of toughness compared to the neat polymer. A new concept is the usage of filler particles as toughening agents [11]. In this paper, a complete study on the applications of nano PCC mineral fillers is the best in recycling polymers and composites is carried out, and also the future challenges in this area are discussed which can help the researchers in the potential works.

2. ADVANTAGES AND DISADVANTAGES OF MINERAL FILLERS

Traditionally, fillers were considered as additives, which, because of their unfavorable geometrical features, surface area and chemical composition, could only moderately increase the modulus of the polymer, whereas strength (tensile, flexural) remained unchanged or even decreased. Their major contribution was in lowering the cost of materials by replacing the most expensive polymer; other possible economic advantages were faster molding cycles as a result of increased thermal conductivity and fewer rejected parts due to warpage.

The term reinforcing filler has been coined to describe discontinuous additives, the form, shape, and/or surface chemistry of which have been suitably modified with the objective of improving the mechanical properties of the polymer, particularly strength. Inorganic reinforcing fillers are stiffer than the matrix and straighten, causing an overall reduction in the matrix strain, particularly vicinity of the particles, as a result of the particles closely associated with matrix. As shown in the Table. 1. Fillers and chemical families for plastics.



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Table 1. Fillers and chemical families for plastics

Chemical Family Examples

Inorganic salts CaCO3, BaSO4, CaSO4, phosphates, and hydrotalcite.

Silicates Talc, mica, kaolin, wollastonite, montmorillonite, feldspar, and asbestos

Inorganic oxides Glass (fibers, spheres, hollow spheres, and flakes),

MgO, SiO2, Sb2O3, Al2O3, and ZnO.

Hydroxides Al(OH)3 and Mg(OH)2

Metals Boron and steel

Organics

Carbon, graphite

Carbon fibers, graphite fibers and flakes, carbon nanotubes,

and carbon black

Natural polymers Cellulose fibers, wood flour and fibers, flax, cotton, sisal, and starch

Synthetic polymers Polyamide, polyester, aramid, and polyvinyl alcohol fibers

Improving the physical properties of nanocomposite materials with polymeric matrices are remarkable and well known, but the toxicological effects of mineral fillers and derived nanocomposites are currently being investigated with increased interest. In this sense, this work focused on our views of the published reports related to the analysis of the toxicological profile of commercial and novel modified mineral fillers and derived nanocomposites.

2.1. Talc

Talc is magnesium silicate mineral filler and pulverized talc has wide industrial applications in cosmetics as body and face powder, filler in rubber and plastics industry, but natural talc also presents a number of disadvantages. Particularly, natural talc ores consist of a mixture of several minerals like asbestos, etc. and natural talc structure presents some cationic substitutions [12] and, consequently, is inhomogeneous size distribution [13].

Nano powder of talc is a recent introduction and is used for improving quality of many industrial applications in plastics for higher strength and stiffness, better thermal and creep resistance, owing to their unique nano-size, nanoparticles are provided with many special physicochemical properties, and thereby may yield extraordinary hazards for human health [14-18]. Since, talc with a multitude of physical and functional characteristics is used for particular applications, so occupational and environmental exposure to nanoparticles of talc has obviously increased.



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Talc miners have shown higher rates of lung cancer and other respiratory illnesses because talc is the most effective pleurodesis agent, which contains dangerous silica and asbestos [19, 20]. The common household hazard posed by talc is inhalation of baby powder by infants [21] and has been used for several pleural diseases, such as malignant pleural effusion [22, 23] and pneumothorax [18]. Fig (2) shows that the talc poudrage are stored in lungs [24].

FIG: 2. Three cases of pleural effusion receiving talc poudrage using a catheter technique with flexi-rigid thoracoscopy under local anesthesia [24].

Nano powder of talc is a recent introduction and is used for improving quality of many industrial applications in plastics for higher strength and stiffness, better thermal and creep resistance, owing to their unique nano-size, nanoparticles are provided with many special physicochemical properties, and thereby may yield extraordinary hazards for human health [19-23]. Since, talc with a multitude of physical and functional characteristics is used for particular applications, so occupational and environmental exposure to nanoparticles of talc has obviously increased.

2.2. Clay Clays and clay minerals belong to the phyllosilicate group, these minerals are very small and

their preferred formation occurs under the surface conditions [25]. Clay minerals are widely used in industries, engineering and construction applications because their physical and mechanical properties [26]. Currently, the use of several clays in the food industries is a reality for improving food packaging.



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Although the beneficial effects of the nanocomposites obtained from clay minerals have been known for years and are generally well described, but the toxicological effects and impact of clay minerals and derived nanocomposites on human and environmental health are currently being investigated with increasing interest.

The incorporation of the clay minerals into polymers can result in non-intentional exposure to the consumer, and it is thus necessary to evaluate not only the micro structured clay, but also the imbued nanomaterial in the polymer due to the possible migration to the food product [27-29]. Moreover, humans can absorb clays through occupational and environmental exposures and also due to their presence in consumer products (pharmaceutical formulations, spas, and beauty therapy) [30]. In contrast, the presence of clays in the environment and their effects on wildlife can also be derived from intentional and non-intentional sources.

Several researchers have already evaluated the in vitro toxicological profile of different clays and derived nanocomposites, in vitro studies suggest that the interaction of clays with organs may provoke healthy-deleterious consequences, to date, there is a little mechanistic understanding of the physiological effects [31], and cytotoxicity with different essential mechanisms such as necrosis/apoptosis, oxidative stress and orgenotoxicity due to exposure of clays [32]. Verma et al. [33] assayed that the tubular nano clays more cytotoxic than platelet and other physical structure of clay minerals in lung epithelial cell, and also the effects related with reactive oxygen species (ROS), generation and other disorders in several target cell lines exposed to different unmodified and modified clay minerals and derived micro / nano composites [34-44]. Elmore [45] reported that different clay minerals induced cytotoxicity in several macrophage-type cell lines and have haemolytic activity toward the red blood cells of different species. Additionally, it has been reported that clay minerals may promote infection by a direct cytotoxic effect on neutrophils, making them unavailable for bacterial phagocytosis [46]. However, Different clays have their own cytotoxic profile with dependence on the experimental conditions (type of clay, modifier, cell line, concentrations used etc.), these all toxicological evidences that in vitro researchers on clays is of high interest nowadays. Table.2. shows that different toxicological evidence of clays and derived composites.



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Table 2. Toxic effects of unmodified/modified clays and derived composites.

Clay Composites Modifier Concentration time

Exposure time

Toxic effect

Native Bentonite Modified Bentonites

Unmodified 1-50ug/cm2

20ug/mL1g/L

24h All bentonite samples induced cytotoxic effects [46].The bentonite samples induced necrosis as well as apoptotic cell death [46].Bentonite particles induced apoptosis [43].

Aminopropyl magnesium phyllosilicate (AMP)Aminopropyl calcium phyllosilicate (ACP)

Amino propyl 1-1000ug/mL 24, 48, 72h

Decrease in cell viability and membrane damage appeared at the highest concentrations of both organoclays assayed [47].

Clay2 HDTA+ Acetylcoline

0-88ug/mL Genotoxic effects were observed in cells [37].

C30B Quaternary ammonium salt

88 ug/mL

0-40 ug/mL

24, 48h Cytotoxic effect and DNA damage was observed in HepG2. [41].Increased ROS and decreased GSH content at the highest concentration [42].

CNa+C93A

Unmodified 50 and 1000ug/mL

24h Cell Death was observed after exposure to nano clays [40].

Mt Unmodifies 0-1000ug/mL ROS production was observed [34].

Sepiolite nanoclay particulates- Quarz (SiO2)

Unmodified 1-5mg/Kg bw 1-3moths Sepiolite resulted in multinucleated giant cells at 1, 5 weeks and 3 months increased BAL fluid lactate dehydrogenase values at 24h Transient increases in cell labeling indices in the high dose group Lung inflammation. With increased time post installation, pulmonary changes became less severe. [48].

Bentonite nanoclay Not available Not available 28 days Reduction of the relative weight of the liver, the activity of its conjugating enzymes, hyperproduction of colonic yeast microflora [49].

2.3. Kaolin



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Kaolin is also one of the phyllosilicate mineral, the physical and chemical properties of kaolin depends on its structure and composition, generally kaolin is used as a filler in rubber, paper and plastic industries. But the toxicological effects of kaolin nanocomposites are currently being investigated and the extensive number of reports also available. Long-term exposure to kaolin causes the development of radiologically diagnosed pneumoconiosis in an exposure-related manner, kaolin, and other clays often contain quartz, and its exposure is usually related to silicosis and lung cancer. Significantly increases the incidence of mortality from chronic bronchitis and pulmonary emphysema has been reported after exposure to quartz [50]. Gao et al. [51], also explained the Kaolinite and quartz, both compounds induced cytotoxic effects on rat pulmonary alveolar macrophage cells starting on the first day of exposure as shown in Table 3.

Table 3. Toxic effects of Kaolin.

Kaolin Modifier Concentration Exposure time

Toxic effect

Kaolin Unmodified 0.1mg 24h Kaolin induced morphological changes, including lysis of the cells was observed. [53]

Kaolinite Unmodified Not-Specified Not-Specified

After kaolinite exposure high ROS production was observed [35].

Kaolin Untreated/Treated

0-40ug/mL Not-Specified

Genotoxic effects were observed in all cases [51].

Kaolin Unmodified 20% kaolin Not-Specified

Rats fed kaolin diet exhibited maternal anaemia and reduction in the birth weight of the pups. [54].

Kaolinite, Clay Unmodified 150-450mg/kg bw

Not-Specified

The ingestion of kaolin and clay causes a progressive increase of metals in the urine and presumably in blood [55].

Kaolinite Not-Specified

Not-Specified 28 days Significant increase in the thickness of villi, lengthening of the apical microvilli and increased mitochondrial replication. Stimulation of the absorption of long chain fatty acids. Kaolinite is dissociated in the lumen and all passes directly through the intestinal barrier. [56].

Bonglaisin et al. [52] reported that kaolin contaminated with high amount of heavy metals like A Monthly Double-Blind Peer Reviewed Refereed Open Access International e-Journal - Included in the International Serial Directories


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Pb, Cd and Hg. European union alerted the Cameroon Ministry of public health that kaolin carried Cameroon to Europe had abnormally high amount of lead (Pb) at levels at 100 times higher than the maximum permissible levels. These contaminated heavy metals getting into the human food chain through eating contaminated kaolin clay are known to be very toxic to humans; in general population exposure to low concentrations of kaolinite, and other clay minerals in their natural form are ubiquitous [50] that are more frequently used in food packaging.

The improvements of that mineral fillers used in several industries, but different fillers have their own toxicological profiles. In this sense, the variability of the toxicity results described in the scientific literature are huge, as was shown in this review. However, these disadvantages of mineral filler should replace with other composite fillers that have best enhancing functional properties for industries, abundant nature and inexpensive safety mineral. Precipitated calcium carbonate (PCC) is one of the most important mineral filler and widely used in paper, plastics, paints and recycled plastics industries than other fillers, because it’s abundant nature, eco-friendly and cost effective.2.4. Precipitated Calcium Carbonate (PCC)

CaCO3 is an exceptional mineral and amongst the most widely occurring natural minerals, approximately 4% of the Earth’s crust consists of CaCO3 in the form of limestone, chalk or marble [57]. CaCO3 minerals are the building blocks for the skeletons of many marine organisms, for example the shells of molluscs. The natural material is often used without purification, but for more demanding applications CaCO3 is purified by precipitation to produce PCC and it is a material of great interest due to its large range of other industrial applications and it is widely used as polymer composite; filler for ceramics and rubber, paper, ink, cosmetics, toothpastes, additives for plastics, and detergents; a component of pharmaceuticals and foodstuffs as well as numerous uses in electronics and catalysis.

There are several mineral fillers are available, but among those fillers, Precipitated Calcium Carbonate (PCC) from limestone has long been recognized as a versatile additive and its importance as functional mineral filler is well known, because limestone is a naturally abundant, inexpensive and safety mineral and it is widely available around the world, easy to grind or reduce to a specific particle size, shape are critical to their multifunctional and compatible with a wide range of polymer resins [58-62].

Currently utilization of precipitated calcium carbonate (PCC) gradually increases worldwide in various fields because CaCO3 has several different schemes of atomic arrangements, called polymorphs, meaning they all have the same chemical composition, but different crystal structures and symmetries. The polymorphs of CaCO3 include three anhydrous (calcite, aragonite and vaterite) and two hydrated (monohydro calcite, CaCO3.H2O and ikaite, CaCO3.6H2O) crystalline phases, and amorphous calcium carbonate (ACC) [63]. Generally, the hydrated and amorphous forms are metastable and show the tendency towards rapid transformation into calcite, aragonite, or vaterite. The thermodynamic stability of the crystalline anhydrous polymorphs at ambient conditions decreases in the order of calcite, aragonite, and vaterite [64], whilst their typical morphologies are classified as rhombohedral calcite, needle-like aragonite and spherical shape vaterite, respectively [65]. Table. 4. Shows Physical properties of the different Calcium carbonate phases.



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Table 4. Physical properties of the different Calcium carbonate phases.

Property Calcite Aragonite Vaterite

Formula CaCO3 CaCO3 CaCO3

Crystal Shapes

RhombohedralScalenohedralColloidalTrigonal

Needle/whiskers shapeFiber shapeOrthorhombic

Hexagonal

Density/g.Cm3

2.71 2.93 2.65

Abundance Very Common Common Rare

Calcite is stable at thermo dynamical equilibrium phase of CaCO3 at ambient temperature and pressure [66]. The calcite crystal system appears in a range of morphologies with the most common being the rhombohedral, often shaped as cubes and the scalenohedral forms [67]. Aragonite has the same chemical composition as calcite but a different structure and crystal shapes, it usually forms needle-like orthorhombic crystals and its formation is favored at higher temperatures and pressures [68, 69]. Other morphologies of the aragonite polymorph, such as multi-layered [70], pseudo-hexagonal [71], lamellar-like [72], rod-like [73], and dendrite-like [74] have also been synthesized under various experimental conditions.

Vaterite is also the same chemical composition as calcite and thermodynamically least stable of the three crystalline polymorphs, and it has the highest solubility of the three polymorphs and transforms by dissolution and re-crystallization into a more stable modification over time when in contact with water [75]. Vaterite is expected to have potential applications for various purposes due to its special properties such as high solubility, high dispersion, high specific surface area and lower specific gravity compared with the other two crystalline forms, calcite and aragonite [76].

However, the different polymorphs of CaCO3 (i.e. calcite, aragonite and vaterite) can have different functions as additives to act as functional active fillers. Owing to its larger specific surface and higher surface activity and also dispersion can be increased if cubic calcite crystals are added to paper and paint industries [77]. Polyvinyl alcohol or polypropylene composites with aragonite filler showed improved impact strength, tensile strength, glass temperature and decomposition temperature [78,79], while paper coating containing aragonite benefits from improved brightness, opacity, strength and printability [80,81]. Acicular or needle-like aragonite crystals have a reinforcing effect on rubber and plastics [82], vaterite can be used as filler for the improvement of mechanical properties of materials [60, 83] and spherical vaterite particles have a significant impact on the brightness and transparency of ink [84]. Therefore, controlling the structure and morphology of CaCO3 particles is an important subject for research and development.



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2.4.1. Global Consumption of Ground Calcium Carbonates and Precipitated Calcium Carbonates (PCC)

The global demand of calcium carbonates rising continuously and it would reach nearly 5500 tons by the year 2011 to 2016 (Fig.3). Both ground calcium carbonates (GCC) and precipitated calcium carbonates (PCC) demand continues to increasing as paper coating applications as well as mineral fillers for plastics industries and it represents the largest type of calcium carbonates. Recently, precipitated calcium carbonate (PCC) and nanocalcium carbonates were used for polypropylene composites in both paper and plastic industries. Among the global consumption of calcium carbonates, Asia is expecting to occupy major part, particularly in paper industries in near future.

Fig.3. Estimated consumption and forecast demand for GCC and PCC by market, 2011 and 2016(000t).

Source: Roskill Presentation, 2011

2.4.2. Limestone

Limestone rock is a natural resource and is the preferred raw material for the production of PCC in several industries. The replacement of natural limestone by waste-derived products as feedstock for PCC production would contribute towards a more sustainable use of a country’s natural resource of limestone. Modern society uses vast amounts of resources and produces equivalent amounts of waste that must be managed to avoid environmental problems.



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The reduction and re-use of waste has therefore become more financially viable, particularly through the development and/or application of innovative solutions and emerging technologies. Mineral carbonation is one of the carbon capture and storage technologies that has received increasing attention because of its safe and essentially permanent chemical conversion of CO 2 into stable carbonate minerals [85-88]. Aqueous mineral carbonation involves the reaction of CO2 with calcium and/or magnesium-bearing minerals in an aqueous suspension [89].

Industrial solid wastes that contain large mass fractions of calcium (Ca) are of great interest in the mineral carbonation process as it can combine the economic benefits of producing a valuable carbonate material (PCC) whilst improving the quality of the industrial residue for disposal or re-use as well as to reduce the overall quantity of CO2 emitted [90-92]. The aqueous carbonation of alkaline industrial solid wastes minerals can be performed in the carbonation process involves the reaction of CO2 with solid calcium-bearing minerals in an aqueous suspension for the production of PCC of high quality and purity [89]. The industrial solid waste residues are used for the production of PCC include steelmaking slag [93-96], red mud [97, 98], fly ash [99,100], oil shale ash [101], flue gas desulphurization (FGD) and gypsum [102, 103].

2.4.3. PCC Synthesis from Limestone

The precipitation of calcium carbonate (CaCO3) by a carbonation process is the most economically efficient processes existing today. The conventional carbonation process for PCC production uses mined, crushed limestone as raw material. Crushed limestone is burnt in a lime kiln at about 900°C - 1000°C, where it decomposes (calcination) into calcium oxide (CaO) and CO2. After the calcified lime has been treated with water, the resulting milk of lime is purified and carbonated with the carbon dioxide obtained from the calcination process.

Calcination of limestone CaCO3 CaO + CO2] (1)

Slaking of quicklime CaO + H2O Ca(OH)2 (2)

Precipitation Ca(OH)2 + CO2 CaCO3 (PCC) + H2O (3)

However, the control of CaCO3 polymorphism and morphology remain an important ongoing research area because the application of CaCO3 powder is determined by a great number of defined parameters, of which polymorphism and morphology are considered to be the most important [104]. The industrial PCC production aims at controlling the phase, morphology, and physical properties (i.e., particle size, specific surface area) by controlling the reaction temperature, Carbondioxide partial pressure, CO2 flow-rate, lime slurry concentration, and agitator speed [105, 106].

3. RECYCLED PLASTICS



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The ever increasing tonnage of plastic waste has driven the need for sustainability of renewable resources through plastics recycling. Nowadays, many products are manufactured using recycled plastics, including decking boards and garden sleepers for children’s playground [107]. Recycling plastics are exits some disadvantages of mechanical properties when compared to virgin polymers, because they generally exhibits lower stiffness and strength, however materials can be incorporated and reinforced into the polymer matrix and restore their mechanical properties and extend the life spans of the recycled plastics composites, these materials are often called mineral fillers [108]. Putra et al. [109] demonstrated that certain fillers (Calcium carbonate, Talc and Fiberglass) can be added to recycled LDPE and HDPE to improve their mechanical properties.

3.1. Advantages of recycling plastics

The question of the logistics for waste reprocessing has been a constant problem across different topics related to the management of health, safety and environment of states throughout the world. A serious obstacle is the little awareness of the different stakeholders. The society, in general, has a great difficulty in becoming aware of the effective need for separating the different types of waste generated daily. The authorities do not provide resources for establishing a selective collection, by those who live of collecting discarded wastes, whether in the streets or in landfills. Those people, for their limited background or little education are constantly exposed to all sorts of health problems, because they have no information centers to receive a basic knowledge on health and safety.

At the end of this segment are the recycling stations an activity still marginal which do not face an effective audit from the different inspection agencies and also do not divulge information nor make available resources so that their activities can be carried out in acceptable conditions in terms of health, security and environment.

With regard to the segment of plastics, Pereira [110] explained that the major impacts on health, safety and the environment identified in PP and PET (polyethylene terephthalate) recycling, in the State of Rio de Janeiro are changes of landscape, conditions of water bodies, useful life of landfills, quality of groundwater, atmospheric emissions, noise and public health risks and damages to the health of the workers in this segment [111].

Several end-of-life options exist to deal with plastic waste, disposals and incineration with or without energy recovery. The plastics recycling rate was 21.3% in 2008, helping to drive total recovery (energy recovery and recycling) to 51.3%. The highest rate of recycling is seen in Germany at 34% and the lowest in Greece at 8%. Plastic recycling needs to be carried out in a sustainable manner and recycling process is attractive due to the potential environmental and economic benefits. There are a wide variety of recycled plastic applications and the market is growing.

3.2. Recycling plastics Global trend and Applications



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As plastic packaging has the longest established system for the recovery and recycling of plastic waste, this process is higher than those of other streams; mainly it is followed by agricultural waste plastic and to economic incentives for the availability of homogenous materials. Although wastes of electrical equipment of automotive industries and construction plastic waste sources are generally low rates of recycling process, but the rate of energy recovery is relatively high and the total recovery is highest for plastic packaging at 59.8% and lowest for end of life vehicles plastics at 19.2%.Plastic recycling needs to be carried out in a sustainable manner and also attractive due to the potential environmental and economic benefits. There are a wide variety of recycled plastic applications and the market is growing throughout the world.

4. PRECIPITATED CALCIUM CARBONATES(PCC) FOR RECYCLING PLASTICS

The mineral filler plays an important role to enhance performances in polymers, fillers greatly improves the work ability of fresh or recycling polymers like plasticity, cohesiveness and superior lubricating properties in plastics. The filler decreases the quantity of polymer resin for mixing with fillers, and increases adhesion by increasing the viscosity [112]. Polymer composite properties are influenced by the dispersion of fillers and the presence of aggregates. The dispersion of rigid fillers in a plastics and rubber phase is a good way to improve the compatibility between fillers and the matrix [113].

The current study shows that the application of nano fillers can be an efficient technique for recycling of polymers, composites and blends, because mineral fillers mechanically to ensure a good bond between the polymer matrix and the inorganic aggregates and it have been used for recycling which should be developed for all waste polymers, and also it is indicated that the application of a compatibilizer for recycling of polymers, particularly blends and composites are more useful. Precipitated calcium carbonate (PCC) is widely used as a filler for preparation of recycled plastics. Table.5. is shown that the different concentration of nano PCC has a positive effect on recycling plastics and also, the application of mineral fillers compatibilizer causes a more improvement of performance.

Table 5. Different concentration of PCC has positive effects on recycling plastics



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Mineral filler Particle size

Recycling polymers (%) Nano composites

Improving performance

Precipitated Calcium Carbonate

(PCC)

106 : 5 m PP/rHDPE

PP/rHDPE/EPR blends

30% CaCO3 Improve mechanical properties [1]

rHDPE (Bottles) 30% CaCO3 Density increased [2]

5-15 µm rHDPE (Milk Bottles) 30% PCC

40% PCC

Tensile strength

Young Modulus [3]

rPET 30%PCC Creep strain [4]

80nm 30% rPP 6%PCC Tensile strength at break

Elongation at break [5]

3 µm rPP 10-30% PCC Mechanical properties [6]

Not-Specified

rPP

(Post-consumer waste PP)

5.17% PCC Thermal properties [7]

Not-Specified

rPP/HDPE 15% PCC Flexural strengths [8]

Not-Specified

1- 20% rPE 0.04-0.8% PCC Mechanical properties [9]

Not-Specified

rPP 10-20% PCC Youngs Modulus and Izod Strength

Albano et al,[114] focused on virgin polymer associated with recycling plastics can improve the mechanical properties. In the present investigation proved that PP/rHDPE/EPR blends combined with 30% CaCO3 mineral filler is most beneficial for improving the mechanical and thermal properties for recycling plastics. Chariyachotilert et al [115] also suggested on recycled HDPE drinking water bottles, in this study, he investigated the mechanical properties of recycling HDPE by the adding with CaCO 3 as



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plastic filler. The results showed that increase in CaCO3 filler loading up to 30% (w/w), the density of recycled HDPE significantly increased and also 20% recycled HDPE associated with 10% CaCO3 in order to keep the mechanical properties like Tensile strength and elongation at break of recycled HDPE products in close proximity to those of virgin resins.

Byung-Wan Jo et al, [116] attempt to predict long term creep using short-term creep and define the characteristics of creep behavior of polymer concrete (PC) bound by recycling-polyester (rPET) resin. The recycled-PET-PC shows more than 20% of its long-term creep within the first two days, and about 50% during the first 20 days. The creep strain of PC without a filler is much higher than that of PC combined with filler, because the filler plays an important role in restricting the deformation of PC and also, as far as the type of filler is concerned, the effect of 30% CaCO3 as a filler on polymer concrete is better in terms of the decreased creep strain and specific creep, these indicated that the PCC have larger surface area of particles and the higher adhesion between the resin binder and the aggregates.

Hesam Ghasemi et al [117] reported that the post-consumer waste (PCW) raw materials were proved less performance of Polypropylene and it contains inorganic impurities. XRF and XRD showed that the inorganic content of PCW was 6wt% of CaCO3 was present in post-consumer wastes. Even though many reports suggested that the post consumed waste of recycled Polypropylene (rPP) was used can improve the mechanical properties with CaCO3, Branka et al., [118] proved that the mechanical properties of recycled Polyvinyl chloride (rPVC) with Nano CaCO3, in this study, they have to use 3% virgin PP is associated with 30% recycled PVC polymer shows weak melting point depression [119] and worsens mechanical properties and further addition of 6% CaCO3 nano filler improves the higher mechanical properties like tensile strength and elongation break of both rPVC and PP composites was observed.

CONCLUSIONS

The application of mineral fillers can be an efficient technique for recycling of polymers, composites and blends. Various mineral fillers like Talc, Clay and Kaolin etc. are widely used in several industries, but their toxicity profile currently has many gaps. In this sense, the variety of the toxicity results were described in the scientific literature is huge, as was shown throughout the review. Among those fillers Precipitated Calcium Carbonate (PCC) from limestone has long been recognized as a versatile additive and its importance as functional mineral filler is well known, because limestone is a natural abundant, inexpensive and safety mineral and it is widely available around the world. However, with the objective to a successful and economic recycling in which the recycled polymer has more acceptable characteristics, more investigation must be made on the whole aspect of recycling process to enhance the competitiveness in these systems. PCC is the most widely used fillers in recycling plastics because of its low cost and superior mechanical properties than other fillers and much effort has been driven to increase mechanical properties such as tensile and flexural strength, impact resistance. In conclusion, many benefits could be derived from Calcium carbonate minerals and their products in several industrial applications with safety and cost effectiveness.

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