Polymer Composites Based on Plasticized PVC and Vulcanized Nitrile Rubber Waste Powder for Irrigation Pipes

The paper presents the technique of production and characterization of polymer composites based on plasticized PVC and rubber powder from vulcanized nitrile rubber waste. The new polymer composites have lower hardness, higher elongation at break, a better tensile strength, and better ozone resistance, and the blend suitable for irrigations pipes for agricultural use was selected. The selected polymer composites have a good behavior under accelerated aging, repeated flexion at room temperature and at low temperature (−20C), a very good behavior for immersion in water, concentrated acid and basis, animal fat, soya, and sun flower oil, proving their suitability for gaskets, hoses, protection equipment, rubber footwear, and so forth. The resulted thermoplastic polymer composites can be processed by injection, extrusion, and compression molding.


Introduction
An efficient reclaiming of wastes resulted from the manufacture of mechanical rubber goods can be achieved by their use in producing composite thermoplastic elastomer materials [1,2].These composites can be used as thermoplastic material substitutes.Such substitutions can result in lower costs because of savings in thermoplastic materials while enabling the industrial rubber wastes to be reclaimed.Furthermore, the manufacture of such materials yields no wastes because of the spews and refuses being recycled.Composite materials based on thermoplastic and rubber powder are produced by mixing a dispersed elastic filler and a thermoplastic in a melt at a temperature above the melting point of the thermoplastic matrix on extruder-granulator, in Brabender plasticorder or on electrically heated roller mill.These materials are processed/moulded by a technique similar to those used in pro-cessing plastics and rubber blends (pressing, injection, extruded, etc.) [1][2][3][4][5][6][7].
The paper presents our work for producing polymer composites based on plasticized PVC and rubber powder from vulcanized nitrile rubber (NBR) waste and testing their characteristics.It deals with fitting the material characteristics in the standards for materials used for irrigation pipes.
Poly (vinyl chloride) (PVC) is a versatile polymer, used in flexible, semirigid, and rigid forms.In worldwide plastic production, it is second only to polyolefins.The rapid expansion and consumption of PVC is due to lower cost, greater availability, good mechanical properties, and diversity of its properties [8,9].One of the most prominent needs for PVC in application end use is permanent plasticization.A very important and commercially significant blend is that of NBR and PVC.NBR acts as a permanent plasticizer for PVC, and at the same time PVC improves the ozone, thermal ageing, and chemical resistance of NBR.The presence of PVC improves aging resistance of NBR as both PVC and NBR are polar, and blending NBR with PVC increases the compatibility [10,11].
Regarding this aspect, composites based on PVC/vulcanized NBR rubber powder do not need any compatibility agents in order to improve their characteristics.(2) Preparing the experimental polymer composites based on plasticized PVC and NBR rubber powder on the laboratory electrically heated roller mill.Process variables were as follows: temperature: 140-170 ∘ C, friction coefficient: 1 : 1.24.The ingredient addition sequence: plasticized PVC (7-15  ), rubber powder (5-10  ), homogenization, and removing from the roller mill (3-5  ).

Experimental
Table 2 presents the recipe of NBR rubber powder/PVC plasticizing blends.
The resulted polymer composites were granulated in a laboratory extruder granulator, equipped with a heating system (at 160-175 ∘ C) in three stages, a granulating device, knives, and cooling system.
Test samples intended for the blend characterization were prepared both by compression molding into 2 × 150 × 150 mm

Reference number
Ingredients/blends C1 C2 [1] NBR rubber powder, g 75 135 [2] P V C , g 1 5 0 1 5 0 [3] DOP, g 75 75 [4] L G R 8 0 0 8 , g 6 6 [5] Zinc stearate, g 0.75 0.75 [6] Uvinul 5050, g 1.5 where  0 is the initial length between two marks and  is the length between the marks 1 minute after the sample broke in a tensile test.Accelerated ageing trial was done according to SR ISO 188/2007 using the hot air circulation oven method.Similar samples to those used for tensile testing and for hardness determination were used.Test duration was of 7 days and temperature of 70 ± 1 ∘ C. The results were compared with those from samples not subjected to ageing.
The densities of elastomer samples were measured according to ISO 2781/2010 (the precision and the uncertainties of the test are ±0.09).
Determining abrasion resistance was done according to ISO 4649/2010, the cylinder method, using a pressure of 10 N. Abrasion resistance was expressed by relative volume loss in relation to calibrated abrasive paper.A wearing tester with abrasive cloth and abrasive based on normal electrocorundum on dressed cloth substrate with granulation of 212-80 m (PE 80), whose abrasiveness must be of 180-220 mg control rubber.The samples used were obtained from rolled blends and pressed by cutting with a rotating die and have cylindrical shape, with a diameter of 16 mm and height of min.6 mm.The precision and the uncertainties of the test are ±0.15.
Flexion resistance (Ross Flex) was determined according to SR 7645/1994.Samples were obtained by punching rubber plates and have rectangular shape.The trial was performed using a Ross Flex device, monitoring crack marks on each sample at intervals of 1 h, 2 h, 4 h, 8 h, 24 h, 48 h, 72 h, and 96 h.The precision and the uncertainties of the test are ±300.
Resistance to swelling by liquids was determined according to ISO 1817/2005 by the change in mass and volume using the following method: the test pieces of known weight ( 1 ) and volume ( 1 ) were immersed in various solvents: water, sun flower oil, soya oil, animal fat, sulfuric acid 70%, nitric acid 50%, caustic soda 50%, isooctane, toluene, 70% isooctane, and 30% toluene solution, in diffusion test bottles and kept at room temperature for 22 h.After immersion, the samples were taken out from the solvents, and the wet surfaces were quickly dried using a tissue paper and reweighted ( 2 ), respectively, ( 2 ).Swelling index (%) was calculated by the following equation: ( The precision and the uncertainties of the test are ±0.04.
For rubber powder, determine the ash in accordance with method a of ISO 247:2006 and determine the acetone extract in accordance with method a of ISO 1407:2011.
All measurements were taken several times and the result values were averaged on three to five measurements.

Results and Discussions
In Table 3, the characteristics of the PVC/vulcanized NBR rubber powder composites are shown determined on injected and compression molded samples.
The data in Table 3 show that the values for physical mechanical characteristics for compression molded samples, and injected samples are similar excepting: (1) a slight decrease of elasticity, (2) a slight decrease of tensile strength and 100% modulus, and (3) a decrease for hardness for C2 from 71 to 65 ShA.The values are in the limits of STAS 10040-74 for irrigation flexible pipes.
The increase of rubber powder quantity leads to an increase of hardness, 100% modulus, tear strength, and a decrease of elongation at break.Similar modification of characteristics due to the increase of rubber powder quantity was determined also by other researchers [2,[12][13][14].
C1 composite was selected for the production of irrigation hose, and further characterization was conducted in order to determine other fields of use.
The results (Table 4) prove that the new polymer composites have a good behavior for accelerated aging (a decrease of hardness of only 1 ∘ ShA and elongation at break and tearing resistance variation is under 5%), behave well on repeated flexions at room temperature and at low temperature (−20 ∘ C), and are resistant to water, concentrated acids and basis, animal fat, soya and sun flower oil, isooctane, and low resistance to toluene and toluene isooctane solution.According to the physical mechanical properties (Tables 3 and 4), the following fields of use were chosen: gaskets (extruded gaskets, general use gaskets excepting oil industry), rubber items for the automotive industry (rubber mats, seals), hoses and rubber pipes (rubber pipes for mud draining, for heating railroad cars, suction hoses, oxygen and acetylene welding hose, hoses for mobile irrigation systems, hoses for acid or basic solutions, etc.), rubber footwear, and rubber protection equipment (water and fat resistant boots), and so forth.
[7] monomers being present in the elastomers.Ash value (19.61%) reveals the presence of such fillers as metal oxides (zinc oxide), chalk precipitate, and other passive fillers.HCl insoluble matter value (8.85%) reveals the active filler such as silica precipitate being present in the rubber blends used in preparing rubber waste powder[7].2.1.1.Polymer Composites Preparation.Polymer composites were obtained in two stages: (1) PVC plasticizing and (2) preparing blends based on vulcanized nitrile rubber powder and plasticized PVC.(1) PVC plasticizing was accomplished by plasticizer (DOP) absorption into PVC when mixing in a 2 L vessel of plasticorder PLV 330 Brabender at 70 rpm, temperature of 40 ∘ C for 10 min.For a good thermal stability, temperature stabilizer and antioxidants have been introduced over time.The resulted plasticized PVC is processed into a sheet on a laboratory roll electrically heated, the resulted sheet being used in the next stage in the blend preparation.

Table 2 :
Formulations of the polymer composites based on plasticized PVC/vulcanized NBR rubber powder.
1.5sheets on a laboratory vulcanizing press at a temperature of 160 ∘ C and pressure of 150 MPa for 10 minutes and by injection in a two nest mold using an injection device at 165 ∘ C and 2  cooling time.The molded samples were stored away from light, at room temperature.2.1.2.Laboratory Tests.Mechanical properties of sampleswere measured on a Schopper tensile tester with a nominal rate of the traverse of the moving grip of 460 mm/min.Modulus at 100% strain, tensile strength, and elongation at break tests were carried out according to the conditions described in ISO 37/2012, on dumb-bell shaped specimens of type 2 (the precision and the uncertainties of the test are ±0.64 for tensile strength and ±2.95 for elongation at break).Tearing strength tests were carried out using angular test pieces (type II) according to SR EN 12771/2003.Hardness of materials was measured using the Shore A scale with samples of 6 mm thickness, by using a hardener tester according to ISO 7619-1/2011 (the precision and the uncertainties of the test are ±0.05).Elasticity was evaluated with a Schob test machine using 6 mm thick samples, according to ISO 4662/2009.

Table 3 :
Physical-mechanical characteristics for the polymer composites based on PVC plasticized/vulcanized NBR rubber powder.

Table 4 :
Physical-mechanical characteristics for the selected polymer composites.Properties after accelerated ageing 70 ∘ C × 168 h Hardness, ∘ ShA,