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TOLEDO (SPAIN)NYLON RECOVERY FROM CARPET WASTES THROUGH THE PYROLYSIS UNDER
THE PRESENCE OF ZnO AND THE MILLING BY A METALLIC ROLLING MACHINE
A.Sekiguchi, O.Terakado and M.Hirasawa,Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya University, Japane-mail: sekiguchi.akihiro@e.mbox.nagoya-u.ac.jp

Abstract
A recycling process of carpet wastes has been studied whose recycling is not extensively carried out because of theircomplex combination of materials. A representative type of carpet is arranged in three layers: nylon fibers, adhesives, andbacking materials made of poly(vinyl chloride). We have employed the pyrolysis under the presence of zinc oxide. Nylonfibers could be effectively recovered by the consequent milling treatment from the brittle backing materials. The influence ofprocess parameters, such as pyrolysis temperature and reaction time, on the separation efficiency is discussed.

Keywords: Carpet, Plastic Recycling, Pyrolysis, Milling

1. Introduction

2. Materials and Methods

Carpet tile is commonly used in office buildings. In theUnited States alone, approximately 1.5 million tons ofcarpet fibers are produced annually [1]. Of this amount,approximately 65% is composed of nylon 6 and naylon
66. The European annual production of carpet isapploximately 1.5million tons [1]. As a result, an
enormous amount of polymers waste is discharged, mostof which is in landfills. Pyrolysis treatment is one of theattractive methods, because it enables feedstock
recycling of synthetic polymers with simultaneous volume
reduction of wastes. Recently, thermal decomposition ofvarious kinds of carpets has been investigated [2].
Difficulties of the carpet waste treatment arise from thecomplex combination of the materials. A typical carpet isarranged in three layers. The materials of the top layer
consist of nylon fibers, typically nylon 66. The second
layer is base fabric and adhesive. The materials of thebottom layer are backing materials that are mainly madeof resin of poly(vinyl chloride), PVC, because it is cheap,
commodity polymer, showing good mechanical property,
as well as flame retardancy. Thus, the pyrolysis of waste
carpet results in the emission of chlorinated compounds,
such as hydrogen chloride and chlorinated organiccompounds, which requires the careful emission control.
In our previous works, we showed that degradation
temperature of PVC was lowered and chlorine was fixed
as zinc chloride in pyrolysis of PVC under the presenceof ZnO [3]. It is, therefore, expected that the pyrolysis ofwaste carpets under the presence of ZnO leads to thefixation of chlorine. The decomposed brittle
carbonaceous compounds from PVC are to be removed
from the nylon layer by appropriate mechanical methods.
In the present study, we have carried out pyrolysis ofwaste carpet in the presence of ZnO, and examined theroll-milling treatment to separate the nylon from the PVC
backing material.

The carpet waste, supplied from Showa Seni. Co., wasused in the present study. A sample size was 10mm
50mm5mm with weight of 1.0g. The powder of ZnO
reagent, Kanto Chem. Co., Ltd., was used. It is difficult todegrade only PVC because the degradation temperatureof nylon, 265oC, is very close to that of PVC, 280 oC.
Thus, we constructed a pyrolysis equipment which
consists of hot plate that enables uni-directional heatingof backing materials. Pyrolysis set up is schematicallyshown in fig.1. The dome-shaped reactor consists of anelectric heater (its heated area is 180mm in diameter), anickel plate (120mm120mm2.0mm), and a copper
cover. The nickel plate on which zinc oxide powder wasput, was heated from the bottom side. Pyrolysis wasconducted under helium atmosphere. A sample carpet
waste was dropped onto the powder layer of ZnO.

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Capper cover

WindowHeventMFC

Sample stage

Powdersof ZnO

Temperature
controler

Sample ofcarpetElectric heater

Ni plate

Fig.1 Pyrolysis reactor
After the reaction, the sample was taken out of thereactor and milled by a metalic rolling machine. After that,the sample containing nylon fibers and powder ofbacking material was separated by a screen with themesh of 1mm.

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6th International Symposium on Feedstock Recycling of Polymeric Materials

3. Results and Discussion
1211109

degree of separation

Fig. 2 shows the photograph of nylon fibers separated bya screen. Nylon fibers were well separated from backingmaterial.
Fig. 3 shows the relationship between the degree ofseparation and reaction time in pyrolysis at 270oC. The
degree of separation is defined as follows:

8760204060

80

100120time(min)Fig 3. Relationship between the reaction time and thedegree of separation at reaction temperature of 270oC.
2520

degree of separation

Where w1 is the total weight before the pyrolysis, and w2
is the weight of nylon fibers after separation by a screen.
It is apparent that nylon fibers are recovered mostefficiently at 30min. Presumably, backing materials arenot decomposed enough when reaction time is shorter
than 30min. On the other hand, a part of nylon fibers is
melted and adhere to backing materials when reaction
time is longer than 30min.
Fig. 4 shows the relationship between the degree ofseparation and reaction temperature. The reaction timewas 30min. It is obvious that nylon fibers are recovered
most efficiently at 265oC. The melting point of nylon 66 is265oC, so that the pyrolysis at the melting point is
especially effective for the recovery of nylon 66. Near themelting point, nylon fibers are still solid, while backing
materials are enough decomposed, under the presenceof ZnO, at the temperature slightly lower than the“degradation” temperature of pure PVC.

1510260

265270275

280

temperature

Fig 4. Relationship between the reaction temperatureand the degree of separation when reaction time was 30min.

4. Conclusions
10mm

Fig2. Nylon fibers separated by a screen at pyrolysis
temperature of 265oC and reaction time of 30min. Small
amount of black material, probably carbonaceousbacking material, remains on the nylon fibers.

Nylon fibers were efficiently recovered by the proposed
method combining pyrolysis with milling. It was found thatthe reaction temperature and time considerably affect thedegree of separation. Under the examined conditions,nylon fibers can be effectively recovered at 265oC andreaction time of 30min. Further study on the optimizationof the process should be carried out.

References[1] C.Hihut, D.Captain, F.Gadala-Maria and M.Amiridis,“Review: Recycling of Nylon From Carpet Waste”, Polym.
Eng. and Sci., Vol41, No.9 (2001) pp 1457-1470.
[2] T.Gunji, K.Nakamura, M.Iijima and T.Hatakeyama,“Thermal Decomposition of Carpets and TheirComponents”, Sen’I Gakkaishi, Vol. 58, No. 4 (2002) pp117-121.
[3] B.Zhang, X.Yan, K.Shibata, T.Uda, M.Tada andM.Hirasawa, “Thermogravimetric-Mass SpectrometricAnalysis of the Reactions between Oxide (ZnO, Fe 2O3 or
ZnFe2O4) and Polyvinyl Chloride under Inert
Atmosphere”, Mat. Trans. JIM, Vol. 41, No.10 (2000) pp1342-1350.

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