Mister Chairman, Ladies and Gentlemen …Today I would like to talk about…… The basis of this work is about manufacturing a porous materials from SBR/RR using a chemical blowing agent , which is namely sodium bicarbonate to create foams and to evaluate the sound absorption of this materials.
First at all, from the environmental perspective, let us start from the situation of recycling and reclamation of the waste tires rubber. Large amounts of rubbers are used as tires for cars and trucks, But after along run these tires are not serviceable, it need very long time for natural degradation due to cross-linked structure of rubbers and presence of stabilizers and other additives. this leading to serious environmental pollution. The most obvious hazard associated with the using waste tire as fuel energy in the cement Kevin industry by burning the tires which are extremely detrimental to the environment. It create another problem of air pollution. So that, it is necessary to find new methods for reclaiming and recycling tires to other applications.
The noise from the traffic system and modern industry become more serious issue in our life. Porous material ( fibers, foam ceramic, Rockwool and vegetable binders) (Limit to the high frequency). Perforated panels absorbers ( from plastic or metal) (Too costly for commercial use). Waste tire rubber materials.( more promising). It is an ecological material and cheap. Otherwise, it has a great sound and thermal insulating power, it is a very good vibration damper and it also has a very high resistance to rending, tearing, compression and abrasion. Generally, The ability of the waste tire materials to absorb sound depends on the cell microstructure and solid rubber properties.
Blowing agent is a chemical substance that is widely used in generating the gas expand the rubber, plastic and ceramics to create foam. In other words, it is called ‘baking powder’ this materials. usually generates nitrogen or carbon dioxide by expansion due to chemical responses and thermal decomposition. the pores foams material classified to two types, the first one is open to the outside and permit gas or liquid to flow (open pores). The second is integral to the materials (closed pores). absorb sound energy by the friction with the air that moves inside the pores.
To achieve higher acoustic absorption performance the sound wave must go deep enough inside, the material and not be reflected back directly into the surroundings. By considering our material which consists from rubber molecular chains and micro voids created from the foaming process can be occurring by two main mechanisms. For the first one when rubber particle subjected to the alternating stresses from vibration and sound waves, their forms would become highly elastically deformed due to the movement of rubber molecular chains. which is characterized by the remarkable lag of deformation works by overcoming great resistance, converting into heat energy and dissipating into the environment (That is called damping losses). The second mechanism can be explained by the viscous losses due to the friction between the air and solid face. Speaking of, When the sound waves strike the cell foam surface, the air constituents flow in and/or out of the cell due to sound pressure .These frictional forces convert the sound energy into heat.
Investigate the acoustic Absorbance of new elastomer manufactured from foamed RR and virgin SBR characterizing by impedance tube in order to….. Indeed, Waste and fresh rubber can be mixed to create an open cell structure conducive to good acoustic absorption. But it all depends what material it is . If it is of open cell structure it will provide micro porosity which will enhance Acoustic absorption performance.
Several portions of RR and SBR.
The compounds being then kept at room temperature for 24 h prior to further usage. The final compounded rubber mixture was sent to compress in a molding machine to complete the curing (or rubber vulcanize) at 160˚C for the respective t90 obtained from rheograph. The samples send to compression molding in a press to produce vulcanized test sheets. Vulcanization is a process of chemically producing network crosslinks between polymer chains. Rubber is cross-linked during the molding process, it usually carried out by heating the rubber mixed with vulcanization agents in a mold under pressure.
In this study, cured dumbbell-shaped rubber pieces (about 3 mm thick) were used. The mechanical properties such as strain at break and tensile strength were measured by a tensile machine at room temperature (25ºC) at a constant speed of separation 50 mm/minute.
The acoustic test system comprises of an impedance tube, microphone, speaker and digital analyzer. A sample with 3 mm thickness was set at one end of the tube and a plane acoustic wave propagates parallel to the axis of the tube, for different frequencies in the range from 125 to 2000 Hz. The test procedure details can be found in the full-length paper.
Crosslink density is defined as the number of crosslink points per unit volume. Crosslink density can be divided into two: chemical and physical crosslink density as presented in this schematic, which the chemical crosslink is contribution of the pure chemical crosslinks that result when a rubber material is vulcanized. While the physical crosslink density is composed of both chemical crosslinks and chain entanglements, and is the crosslink density that is physically measured by stress-strain measurements. We are interesting to calculate the crosslink density because that hypothesis mention that the weakly rubber crosslink density have higher damping properties and consequently enhance the acoustic absorption. Any how the cross-link density can be determined using equations presented in this slide.
The measurement of the minimum torque (ML) represents the hardness of an unvulcanized rubber and the maximum torque (MH) represents the value of hardness or the shear modulus of the fully vulcanized rubber. You can see that for both the MH and ML increase with an increasing of RR composition due to the presence of cross-linked gel in the RR. the cure time (t90) which were also summarized in this table increases with increasing of RR that may be due to poor disperse of blowing agent during mixing. It is significant to mention that Sodium bicarbonate is an inorganic salts is poorly dispersed in rubber compositions. The hydrophobic nature is the main reason for the poor dispersion of the blowing agent in the RR compounds. The elongation at break and tensile strength increased with increasing the RR due to increase a carbon black concentration in the mixture. This results in a molecular interaction between the carbon black and the rubber phase. Moreover, Adding RR into fresh SBR leads to enhance the crosslink density because the presence of active crosslinking sites in the RR.
But still all composites shown superior for sound absorption. The decreased in the acoustic absorption performance attributed to the influence of addition reclaimed rubber. As most of you know When incidence sound waves reached materials with high carbon black filler, the sound wave will involve reflection, dispersion, refraction and diffraction of the incident sound waves, and decreasing sound absorption coefficients. In another side, the RR led to increase the viscosity of the composites and restricted the foam efficiency and reduce the pore size ,consequently, reduce the amount of sound energy absorbed in the material. Usually The compounds with higher viscosity, the gas will be restrained and contained within the rubber matrix, led to a reduction in the degree of expansion.
By adding reclaimed rubber to the virgin SBR obtained new polymer composites to behave as acoustic absorption material. This procedures provided material with high acoustic properties and in wider frequency ranges. The homogeneity and porosity of the materials play very important factor to make suitable absorbers. and lastly low-cost composite materials that will absorb sound waves in wider frequency range are strongly recommended and required.
So, that&apos;s all I had for you today. Thank you. I will be happy to answer any questions you have
Grds conferences icst and icbelsh (2)
Acoustic Absorption and
of SBR/RR Foam
Acoustic Absorption and
of SBR/RR Foam
Mr. Bashir Algaily
• worldwide increasing use
of car as the main of
• Massive stockpiles.
• Negative environmental
• RMA reported in 2013.
• (50%) waste tires used as
Porous material Perforated panels absorber Waste tire rubber material
What is Blowing Agent?
to create foam.
It is called ‘baking