With increasing concern about environmental protection and sustainable development, more and more researches are sing gum elastic recycling. Crumb gum elastic, which is automatically broken down from waste Surs rubber into a particulate solid, is an effectual method of recycling and more applications of this demand to be found. The incorporation of the crumb gum elastic into EPDM-based automotive conditions seals is one of the possible applications and can take down the cost of the concluding merchandise. One purpose of this undertaking is to find how much Sur crumb can be added to an EPDM-based conditions seal compound without mostly impacting mechanical belongingss and surface quality. The other purpose is to place whether sulphur remedy or peroxide remedy consequences in better belongingss.
Introduction of Rubber and Surs
Since Gallic scientist Charles Maria de la Condamine brought the first samples of gum elastic to Europe from his travels in South America in 1736, gum elastic has been introduced to Europe for more than 200 old ages. However, rubber merely became a technically important stuff, successfully utilized in industry when an American scientist Charles Goodyear discovered sulphur vulcanisation of gum elastic in 1839 [[ 1 ]] . Today, gum elastic, as one category of widely used stuffs, plays an of import function in modern technology engineering and prosecute new possible applications. Harmonizing to the International Rubber Study Group, the universe ingestion of gum elastics exceeded 20 million metric tons in 2005 [[ 2 ]] .
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The huge bulk of the planetary production of natural and man-made gum elastic is used in Surs. Shown in, a Sur is composed of gum elastic stuffs, C black fillers and some hempen stuffs which provide mechanical strength to optimize the Surs [[ 3 ]] . Natural gum elastic ( NR ) , polybutadiene gum elastic ( BR ) and styrene butadiene gum elastic ( SBR ) are the chief elastomers used to fabricate automotive Surs. These three gum elastics are briefly described in the undermentioned subdivisions.
Natural Rubber ( NR )
The construction of NR is shown below:
NR consists of over 99.99 % of additive cisiˆ1,4iˆpolyisoprene, since trans-1,4-polyisoprene has plastic belongingss. NR histories for about one tierce of entire planetary ingestion of gum elastic. As a non-polar gum elastic, it can be easy blended with a big figure of other non-polar gum elastics such as EPDM. The strain crystallisation belongings of NR vulcanisates supplies high tensile strength and really good tear opposition, every bit good as its high elastic recoil, low hysteresis and low heat build-up in dynamic distortion, which make it suited for bring forthing automotive Surs [[ 4 ]] .
Polybutadiene Rubber ( BR )
The construction of BR is shown below:
With really similar construction to NR, BR is the simplest man-made gum elastic and has some correspondent belongingss of NR. BR is besides a non-polar gum elastic. In the gum elastic industry, more than 90 % of BR production is used in Surs. Because BR has good scratch opposition, it has been widely used in a big scope of Surs including tread compounds, carcase, sidewall and bead compounds. Particularly, BR Surs are rather utile to better ice grip in winter [ ] .
Styrene-Butadiene Rubber ( SBR )
The construction of SBR is shown below:
The one-year ingestion of SBR is the biggest in man-made gum elastic. With good dynamic weariness opposition, aging opposition and scratch opposition, SBR is largely used in tyre compounds. SBR compound is better used for light truck tyres instead than heavy truck or high velocity Surs, since SBR has higher dynamic heat build-up than NR and BR [ ] .
The vulcanisation of gum elastics improves their mechanical strength and makes them better to utilize in many applications. However, unlike thermoplastic stuffs, gum elastic vulcanisates which possess a 3-dimensional crosslink construction can non be melted and are difficult to recycle. The European Tyre Recycling Association estimates that there are about 250 million tyre arisings accumulated per twelvemonth in the European Union ( EU ) , which equals to 2.6 million metric tons of waste Surs. Worldwide, the coevals of new arisings is estimated to be 1 billion Surs every twelvemonth [ ,[ 5 ]] . Therefore, gum elastic recycling, particularly waste Surs recycling, is a tough job which needs to be resolved, since environmental protection and sustainable development are the biggest issues in the universe today.
Today, a great figure of research workers have investigated legion attacks including pyrolysis and incineration, repossessing, crunching, powder, microwave and supersonic procedures to work out the recycling job efficaciously [[ 6 ]] . However, earlier methods such as pyrolysis and incineration cause wellness jeopardies and air pollution, as toxic wastes are produced during combustion. Reclaiming could severely impact the quality of the concluding merchandises. Microwave and supersonic procedures are more expensive for gum elastic recycling. Sing economic and environmental factors, modern grinding technique seems to be an acceptable attack for recycling waste gum elastics [[ 7 ]] . This method reduces the atom size and the surface country, and makes waste gum elastic useable in the cured province [ ] . One recycling application of the technique is to manufacture crumb gum elastic by utilizing it with virgin polymers.
Current Recycling Situation
shows the development of Sur recycling in the European Union from 1992 to 2005 estimated by the European Tyre Recycling Association. With increasing concern about the environment and the development of recycling techniques, the recycling state of affairs experienced a dramatic addition. The proportion of recycling of waste gum elastics and energy usage steadily grew while landfilling of Surs was well reduced. In 2004 – 2005, the European Union recycled about 1 million metric tons of auto and truck Surs, which reached about one-third of one-year arisings in Europe
In add-on, two European Commission Directives: The Waste Landfill Directive ( 1999 ) [[ 8 ]] and The End of Life Vehicle Directive ( 2000 ) [[ 9 ]] were put into force to censor the landfilling of Surs by 2006 and promote the recycling of Surs. Actually, both the EU and most other states have already attempted to command the direction of Surs
demonstrates the temperament of bit Surs and chief application in the U.S. in 2007. The bulk of bit Surs were used as tyre-derived fuel ( TDF ) for energy recovery. About 2.5 million metric tons of bit Surs were utilized for TDF in the U.S. in 2007. Another big part is in civil technology for route and building applications, which consumed approximately a half million metric tons of bit Surs in 2007
The 2nd largest application for recycling bit Surs is ground gum elastic ( crumb gum elastic ) . This simple and environmentally friendly technique consumed 789.1 thousand metric tons of bit Surs in the U.S. in 2007. The land gum elastic market is assuring and is expected to see growing in the hereafter This undertaking is concerned with the recycling of tyre gum elastic as crumb gum elastic.
Normally, crumb gum elastic refers to rubber atoms recycled from rider vehicle and truck bit Surs without any repossessing procedure being carried out [[ 10 ]] . As antecedently mentioned, crunching is a favorable method to fabricate crumb gum elastic. By and large, there are three attacks to crunch waste gum elastics: ( 1 ) ambient grinding, which produces comparatively big crumb with 0.85 millimeters to 2.54 millimeters atom size ; ( 2 ) cryogenic grinding, which makes much finer atom from 0.25 millimeters to 0.8 millimeter ; and ( 3 ) wet-ambient grinding, which can fabricate atom size making about 0.12 millimeter. The atom size of the most frequently used crumb gum elastic ranges between about 0.3 millimeters to 2 millimeters[ 11 ]. A finer atom of crumb gum elastic makes it suited for good processing and bring forthing comparatively smooth extrudates However, the monetary value additions exponentially with the choiceness of the crumb gum elastic atom [[ 12 ]] .
As one type of successful technique for waste gum elastic recycling, crumb gum elastic has several applications. shows recent markets and applications for crumb gum elastic in North America estimated by the Recycling Research Institute. The largest applications include rubber-modified asphalt used to better the belongingss of route building, and moulded gum elastic merchandises such as rug carpet pad, shocking stuff, dock bumpers, roof walkway tablets, gum elastic tiles and bricks In add-on, resort area and other athleticss come uping markets besides have a dynamic demand for crumb gum elastic.
Recently, more and more crumb rubber with finer size was applied to automotive parts: Surs and waterproofing, for illustration. The biggest advantage of this technique is that it can take down the stuff cost, every bit good as cut downing remedy clip. Therefore, this market is expected to hold a significant growing potency.
Automotive Weather Seal
One possible new application for crumb gum elastic is to add virgin gum elastic and blend them homogeneously to fabricate automotive conditions seals and lower the cost of the merchandise. Automotive conditions waterproofing is extensively utilized in window seals, door seals, bole seals, and sometimes hood seals of vehicles. By and large, automotive conditions seals, which have a rod-like form and may be hollow in subdivision, are made of gum elastics or thermoplastic elastomers.
Automotive conditions seals are indispensable for motor vehicles, although they are merely the little parts of automotive constituents. Automotive conditions seals non merely necessitate to protect the rider country from H2O come ining during any sort of conditions conditions and commercial vehicle rinsing, but besides minimise the noise of the air current inside the auto. For door seals applications, automotive conditions seals are of great significance in finding the door shutting attempt and the coziness of operation of the door [[ 13 ]] . Harmonizing to a proving study from Ford Motor Company, about 35-50 % of the force or energy to shut the forepart door is comprised by seal opposition. Weather seal stuffs are designed and manufactured with complicated features including compaction distortion, high extensibility and squeezability [[ 14 ]] .
The stuffs from which automotive conditions seals are made should hold equal mechanical belongingss such as good stamina and scratch opposition. Good conditions opposition is highly of import and they should be immune to cleaning and anti-freeze fluids. In add-on, good surface quality is indispensible where the conditions seals are seeable.
EPDM compounds are supposed to be one of the most appropriate stuffs to bring forth automotive conditions seals. shows some belongingss of automotive window seals made by EPDM compound. Aside from EPDM gum elastic, the compounds chiefly include filler, plasticiser and bring arounding agent [[ 15 ]] .
Ethylene-Propylene Diene ( EPDM ) Rubber
EPDM gum elastic as a type of man-made gum elastic refers to a copolymer of ethene and propene, and a little measure of diene, utilizing accelerators of the Ziegler-Natta Type One type of construction of EPDM is shown below:
Since ethylene-propylene ( EPM ) gum elastic has a saturated molecular construction and is difficult to crosslink, a 3rd monomer, a diene, which resides in sidegroups of polymer ironss, is added to offer dual bonds and consequence in unsaturation to better the vulcanization of the gum elastic.
Three most frequently used dienes in commercial EPDM gum elastics are shown below:
( DCP )
( ENB )
( HX )
By and large, a suited termonomer contains two sets of dual bonds which have different responsivenesss. One needs to copolymerise with staying EPM in polymer ironss ; the other with a higher responsiveness can be vulcanized with sulfur to organize a 3-dimensional crosslinked construction. ENB is the most common and effectual termonomer presents
Since chief polymer ironss of EPDM gum elastic are wholly saturated, every bit good as their non-polar character, chemical inertness and low toffee point temperature, these favorable belongingss make EPDM gum elastic possess first-class opposition to ozone, oxidization and UV radiation, and good opposition to scratch and snap
In add-on, EPDM has the lowest specific gravitation in all the gum elastics and good compatibility with other additives. EPDM can be extended with a great figure of fillers and oils without deteriorating the belongingss substantiallyTherefore, this decreases monetary value and can better processability.
Since a find in the early 20th century illustrated that C black, which is produced by uncomplete burning of many organic substances, could be mostly accepted by natural gum elastic to better its mechanical belongingss, C black has been the most common filler in gum elastic compounds during the past few decennaries [[ 16 ]] .
Carbon black is an cheap stuff and usually really little ( 20-50 nanometer ) and spherical in form. Harmonizing to the production procedure, C black was classified as furnace black, channel black and thermic black. Today furnace black is extensively used in most rubber compounds such as EPDM Carbon black could busy about one-third the volume of EPDM compounds, which can relatively take down the monetary values of concluding merchandises.
When added to EPDM rubber, C black improves its strength by cut downing the mobility of the polymer concatenation. Therefore, mechanical belongingss such as hardness, tensile strength, stamina, and scratch opposition are enhanced. These reenforcing belongingss achieve a peculiarly good adhesive bonding with gum elastic molecules. Additionally, the uniformly distributed atoms can expeditiously cut down plastic distortion
Carbon black besides improves the chemical belongingss of the stuff. It will progressively barricade out the UV visible radiation through into the EPDM gum elastic, and thereby carbon black increases the opposition to oxidization and weathering [[ 17 ]] .
When EPDM gum elastic is assorted with C black filler, the stiffness of the compounds is increased. After the compounds are vulcanized, a cross-linked construction will organize between molecular ironss, which can do the merchandise excessively difficult for normal public-service corporation [[ 18 ]] .
The chief map of the plasticiser is to weaken the secondary bonds such as new wave der waals force between molecules in polymers, thereby cut downing the attractive force between polymer ironss, which make the sections of polymers easy to travel. Consequently, hardness and modulus of the compounds decrease while flexibleness additions. Additionally, plasticiser besides can better the compatibility between additives in the compounds [[ 19 ]] .
By and large, plasticisers are categorised as mineral oils, natural merchandises and man-made plasticisers. Mineral oils have an extended public-service corporation due to comparatively inexpensive monetary value and good compatibility with non-polar gum elastics. Vegetable oils can take down the processing viscousness and better the cohesiveness or filler scattering of the gum elastic compounds
Table 1 Compatibility of Mineral Oils with Various Types of Rubber
+ compatibility good, a-‹ conditionally compatible
Table 1 Compatibility of Mineral Oils with Various Types of Rubber represents four types of mineral oils ‘ compatibility with different gum elastics. Non-polar mineral oil plasticisers are compatible with non-polar gum elastics ; paraffinic oils are particularly compatible with concentrated gum elastics such as EPDM. The content of mineral oils used in gum elastic compounds ranges between about 5-30 phr. In some compounds such as EPDM, larger contents up to 100 phr are being utilized
Bring arounding Agent
The map of a hardening agent is to change over gum elastic molecules into a web by the formation of a crosslinked construction, which makes gum elastic alteration from a thermoplastic to an elastic province and better its mechanical belongingss. The ultimate remedy provinces depend on the procedure of the vulcanisation and the pick of the vulcanisation chemical. EPDM gum elastic can be vulcanized by either sulfur or peroxide.
Elemental sulfur has remained the most of import and widely used vulcanisation agent for gum elastic. For soft gum elastic the doses of about 0.25-5 phr are used, and for difficult gum elastic 25-40 phr of sulfur are sufficient. EPDM gum elastic can be cured by sulfur because a termonomer offers unsaturated bonds responding with sulfur to organize a 3-dimensional construction. The coveted dose of sulfur depends on the type and measure of termonomer in the EPDM gum elastic. For ENB-EPDM, about 1.2-1.5 phr of sulfur are added. In order to obtain the needed fast remedy rate and high remedy provinces, a combination of some gas pedals is indispensable Accelerators such as tetramethyl thiuram disulphide ( TMTD ) , N-tert-butyl-2-benzothiazylsulfenamide ( TBBS ) , mercaptobenzothiazole ( MBT ) , dibenzothiazyl disulfide ( MBTS ) and zinc diethyl dithiocarbamate ( ZDC ) are largely utilised in several research workers ‘ work to accomplish the interactive consequence with bring arounding agent to do the compounds crosslink easy
Another vulcanisation agent is peroxide, which has been known for a long clip for crosslinking. Normally, peroxides are used to crosslink most concentrated gum elastics such as ethylene-propylene ( EPM ) and silicone gum elastic.
Hydrogen peroxides can crosslink the EPDM gum elastic if the ethene concentration is high plenty, since the methyl group in polypropene cut down crosslinking reactions with peroxides and can take to concatenation scission. Therefore, at least 50 mole per centum of ethene is required to obtain a high grade of crosslinking. For the termonomer choice, DCP-EPDM gives a higher remedy rate than other termonomers. In add-on, activators are indispensible for peroxide remedies
Table 2 Properties of EPDM Rubber Crosslinked by Sulphur and Peroxide
at room temperature %
after 5h a„?
Liter: low ; M: medium ; H: high
In comparing with sulphur-cured EPDM, peroxide-vulcanized EPDM shows the better heat opposition and the lower compaction set even at high temperatures while it has the lower tensile strength, tear strength and scratch opposition, every bit good as largely a higher cost ( see Table 2 Properties of EPDM Rubber Crosslinked by Sulphur and Peroxide ) .
Blending Crumb Rubber into Compounds
The undertaking purpose is to add a certain sum of crumb gum elastic into EPDM compounds for automotive conditions seal applications without significantly impacting mechanical belongingss and surface quality. Most crumb gum elastic comes from automotive Surs which are chiefly made of NR, BR or SBR. Unfortunately, crumb gum elastic may unfavorably impact the surface quality of the merchandise and is non rather compatible with EPDM gum elastic. However, NR, BR, SBR and EPDM are all non-polar gum elastics, so EPDM can theoretically intermix with them. No documents were found in the literature refering the usage of Sur crumb gum elastic in EPDM compounds for usage in automotive conditions seals. However, several relevant articles concerned with similar undertakings were found and are discussed in the undermentioned subdivisions.
Similar research by Jacob et Al. utilizing land EPDM vulcanisate with EPDM compound in a window seal application illustrated a possible commixture procedure of crumb gum elastic and rubber compound matrix. First, virgin stuff was put into the sociable and thaw, attach toing with C black, paraffinic oil, paraffin wax, brown factice and other additives. Then, crumb gum elastic was added and assorted. After sheeting out, gas pedals and bring arounding agent were added and assorted into the blends expeditiously in a 2nd phase. As in the automotive conditions seal application, the concluding merchandise was obtained by squeeze outing or sheeting out the blends of crumb gum elastic and EPDM compounds. The preparations used in Jacob ‘s researchfor window seal composing is illustrated in Table 3 Formulations Used Adding EPDM Crumb Rubber into EPDM Compound.
Table 3 Formulations Used Adding EPDM Crumb Rubber into EPDM Compound
Land EPDM vulcanisate
0 – 200
GPF C black
TMTD ( gas pedal )
MBT ( gas pedal )
ZDC ( gas pedal )
During the commixture procedure, proper choice of gas pedals is of great importance and can assist to accomplish crosslinks between crumb gum elastic and rubber compound matrix. Taking NR land tyre gum elastic as an illustration, the mechanism of this crumb gum elastic crosslinked with EPDM compounds is rather similar with NR/EPDM blends. One research investigated the influence of gas pedal type on NR/EPDM blends indicated that TBBS and MBTS could supply good remedy compatibility between the NR and EPDM stage. Besides that, TBBS offered a high remedy province and good mechanical belongingss for the blends every bit good. Although TMTD could give a high remedy rate, it caused remedy mutual exclusiveness and hapless tensile strength of the blends [[ 20 ]] . Table 4 demonstrates the consequence of gas pedals on mechanical belongingss of NR/EPDM blends.
Table 4 Mechanical Properties of NR/EPDM Blends with Different Types of Accelerator
Tensile strength, MPa
Elongation at interruption, %
Modulus at 100 % elongation, MPa
Hardness, Shore A
Tear strength, kN Garand rifle
Rebound resiliency, %
As reported antecedently, a compatibiliser such as maleic anhydride grafted polypropene, maleic anhydride grafted EPM or EPDM could heighten adhesion between crumb gum elastic and the compound matrix focused on a compatibility survey of NR/EPDM blends and found that the incorporation of 10 phr of EPDM-g-MAH copolymer as a compatibiliser into NR/EPDM blends could mostly better their compatibility by making a figure of crosslinks between the NR and EPDM constituents. This resulted in a better homogenous stage distribution and the rheological belongings of the gum elastic blend was significantly enhanced as good. In add-on, the mechanical belongingss such as tensile and tear strength were greatly increased when compared with non-compatibilised gum elastic blends. Another research worker besides found that a Zn oxide activator interacted with a compatibiliser to bring forth an ionic crosslink, which made blends adhere more efficaciously
Crosslinking between EPDM and tyre crumb gum elastic
As stated before, two attacks can be used to crosslink crumb gum elastic to EPDM compounds, and one is sulphur bring arounding. Since NR, BR and SBR are unsaturated gum elastics, sulfur can crosslink the dual bonds in crumb gum elastic with the unsaturated bonds in termonomer of EPDM. Therefore, Sur crumb gum elastic can perchance be crosslinked into an EPDM compound matrix utilizing a sulfur remedy system.
Another method to bring around crumb gum elastic with EPDM compounds is peroxide bring arounding. Research by Wagenknecht et Al. reported that they blended NR land tyre gum elastic with polypropylene elastomeric metals and used peroxide bring arounding to crosslink the crumb into the matrix. The mechanism of chemical reaction in their research is rather similar to what could go on in my undertaking because EPDM is chemically really similar to polypropylene. The stairss of reaction are given in Figure 1.
( a ) instigator decomposition ; ( B ) macroradicals formation ; ( degree Celsius ) grafting onto gum elastic surface
Figure 1 Reactions during thaws blending
Choice of crumb gum elastic
The appropriate size and content of the crumb gum elastic must be added into EPDM compounds for automotive conditions seal applications if the compound is to hold good plenty mechanical belongingss and surface quality. The consequence of atom size and crumb content is discussed in the undermentioned two subdivisions.
Size of crumb gum elastic
The size of the crumb gum elastic is of great importance, since the proper size makes crumb gum elastics have a good scattering in compounds so that mechanical belongingss would non be mostly affected. Normally, as an ingredient in a waterproofing compound, crumb gum elastic needs a atom size non more than 630 I?m Wagenknecht et Al. used an mean size of 400 I?m land tyre gum elastic to intermix successfully into polypropylene elastomeric metals. They besides found that a cryogenic-ground crumb gum elastic non merely met the demand of size, but besides provided a smooth surface after bulge. Other research workers found that crumb gum elastic aggregated easy, so they concluded that an supersonic technique would be another manner to do crumb disperse good and make a smaller atom size which was scope from 5 to 100 I?m. In this manner, the impairment in some mechanical belongingss on incorporation of land gum elastic was fringy, particularly for tensile strength and elongation at interruption which remained about the same. However, the cost of the concluding merchandise additions due to the expensive crumb gum elastic with finer size and dearly-won processing equipment.
Content of crumb gum elastic
The content of crumb gum elastic added into the EPDM compound matrix is another important issue which needs to be taken into consideration. Jacob et Al. compared 0, 50, 100 and 200 phr land EPDM vulcanisate added into the EPDM compounds and found the content of crumb gum elastic could impact some belongingss of the compounds. The consequence of crumb content on physical, rheometer and mechanical belongingss is given in Table 5. They reported that the increasing burden of the crumb gum elastic resulted in an addition of the compounds viscousness and the dice crestless wave, which made the processability weaker and the surface smoothness of the compounds extrudates impaired ( see Mistake: Reference beginning non found ) , severally.
Table 5 Effect of Crumb Content on Physical, Rheometer and Mechanical Properties
Crumb gum elastic, phr
ML ( 1+4 ) at 120 a„?
Scorch clip t5, min
MH – ML, dN m
Tensile strength, MPa
Elongation at interruption, %
Modulus at 100 % elongation, MPa
Hardness, Shore A
Abrasion loss, cm3 h-1
Tear strength, kN Garand rifle
Jacob et Al. besides explained that with the incorporation of the crumb gum elastic the singe clip reduced due to the migration of gas pedals from land EPDM vulcanisate to the EPDM compound matrix. On the other manus, the minimal rheometric torsion ( ML ) increased because crumb improved the compound viscousness, whilst the maximal rheometric torsion ( MH ) and a?†torque ( MH – ML ) decreased owing to the migration of sulfur from compound matrix to land gum elastic, which resulted in decrease of the crosslink denseness and the remedy rate. These phenomena are illustrated in Mistake: Reference beginning non found.
F0 = no crumb gum elastic ; F50, F100, F200 = 50, 100, 200 phr crumb gum elastic
Additionally, some mechanical belongingss of the compounds such as hardness, modulus, scratch opposition and tear strength bit by bit decreased with the content of crumb ( see Table 5 Effect of Crumb Content on Physical, Rheometer and Mechanical Properties ) . Hence, an appropriate content of crumb gum elastic non merely can take down the monetary value of the concluding merchandise, but besides maintain the mechanical belongingss from big impairment.
As one type of recycling gum elastic, crumb gum elastic is cheaper than EPDM compounds, and hence the undertaking is concentrating on the incorporation of the land tyre gum elastic usually made from NR, BR or SBR with EPDM-based automotive conditions seals to take down the cost. Previous research such as Jacob et Al. had studied on this field, but their research was limited to anchor EPDM vulcanisate with EPDM compounds as window seals. Actually, the land tyre gum elastic is seldom made from EPDM gum elastic and is non rather compatible with EPDM gum elastic.
However, as mentioned antecedently, some research workers argued that certain gas pedals and compatibilisers could assist crumb rubber crosslink with EPDM compounds. Furthermore, the phenomena observed in Jacob ‘s research were of usage as a beginning of mention in the instance of adding land tyre gum elastic into EPDM compounds in my undertaking. Overall, if the optimal combination of crumb content, compounds preparations and bring arounding conditions is achieved, the undertaking will be available for automotive conditions seal applications and possess a immense potency market, every bit good as the part to rubber recycling.