阻燃剂的聚氨酯

Flame retardant properties of polyurethane produced by the addition of phosphorous containing polyurethane oligomers (II)

Yeong-jin Chung b ,Younhee Kim a ,Sangbum Kim a ,*

a Department of Chemical Engineering,Kyonggi University,Suwon 442-760,Republic of Korea

b

Department of Fire &Disaster Prevention,Kangwon National University,Gangwon 245-711,Republic of Korea

1.Introduction

Polyurethane is regarded as a versatile polymeric material since it has comparatively high physical properties and quite easy to prepare.Demand for commercial use of polyurethane is drama-tically increased recently,which might give severe environmental stress due to polyurethane waste.Recycling of these polyurethane waste materials is one of the suitable ways for the conservation of green earth and saving raw materials.The chemical degradation of polyurethane involves the methods of hydrolysis,glycolysis and aminolysis [1,2].However,these chemical degradation methods accompany several critical problems of undesirable byproducts and inef?cient reaction procedures as well as deterioration of mechanical properties in recycled materials prepared by decom-posed reusable products.

In recent days,Troev et al.studied chemical degradation of polyurethane with esters of phosphoric or phosphonic acids to produce phosphorous containing oligomer [3–5].The decomposed products were characterized by NMR and viscometer.They suggested the decomposed oligomers could be reused to synthe-size polyurethane or other polymers.But the recycling process of

polyurethane wastes using alkyl phosphate has not been system-atically achieved yet.

Moreover,the researches on ?ame retardant polymeric material are expected to be activated for worldwide ?ame retardant restriction and requirement of halogen free ?ame retardant.

The ?re resistance of polymer can be improved by the incorporation of numerous ?ame retardants,such as inorganic materials [6,7],phosphorus-containing [8–14]and halogen-con-taining compounds [15].Among them,the thermal degradation or burning of ?ame retardant polymer with halogen-containing compounds releases toxic gases.Therefore,recent developments are toward a ?ame retardant polymer without halogen-containing compounds.The other appropriately ?ame retardant compounds are phosphorus-containing compounds which can avoid the release of toxic gases into the atmosphere.Many researches on the effect of phosphorous containing compounds on ?ame retardant properties have been conducted since the material can provide ?ame retardation of polymer with non-toxicity and good compatibility between polymer and ?ame retardants.

One of the main safety concerns when using ?ber polymer composites is their combustibility.Many polymer composites ignite when exposed to high heat ?ux,releasing heat that can,in some circumstances,contribute to the growth of the ?re.Signi?cant quantities of smoke and toxic fumes may also be released,respectively be limiting visibility and posing a health hazard.

Journal of Industrial and Engineering Chemistry 15(2009)888–893

A R T I C L E I N F O Article history:

Received 6March 2009Accepted 7May 2009Keywords:

Recycling of PU

Thermal degradation Flame retardant

A B S T R A C T

Chemical degradation of used PU was intentionally made by the addition of ?ame retardants such as tris(2-chloropropyl)phosphate (TCPP),triethyl phosphate (TEP)and trimethyl phosphonate (TMP).Final product obtained after the degradation reaction was named as DEP.The structure of degraded products (DEP)was analyzed by FT-IR and 31P NMR and it turned out to be phosphorous containing oligourethanes.Rigid polyurethane foam was produced using the degraded products (DEP)as ?ame retardants.The ?ammability and thermal stability of recycled rigid polyurethane was investigated.The mechanical properties such as compressive strength and tensile strength of recycled polyurethane were also studied.The recycled polyurethane shows reduced ?ammability and higher thermal stability over virgin polyurethane.Mechanical strength of recycled polyurethane also shows as high as that of virgin polyurethane.In order to evaluate ?ame retardant properties of the recycled polyurethane foams with various amounts of DEP,heat release rate (HRR)of the foam was measured by cone calorimeter.Scanning electron micrograph of recycled PU shows uniform cell morphology as virgin-PU.

?2009The Korean Society of Industrial and Engineering Chemistry.Published by Elsevier B.V.All rights

reserved.

*Corresponding author.Tel.:+82312499790;fax:+82312570161.E-mail address:ksb@kyonggi.ac.kr (S.Kim).

Contents lists available at ScienceDirect

Journal of Industrial and Engineering Chemistry

j ou r n al h o m e p a g e :w w w.e l se v i e r.co m /l oc a t e /j i e c

1226-086X/$–see front matter ?2009The Korean Society of Industrial and Engineering Chemistry.Published by Elsevier B.V.All rights reserved.doi:10.1016/j.jiec.2009.09.018

Heat release rate(HRR)has been recognized as a major?re parameter and?re size,smoke production and many others depend on it[16].How to obtain accurate and easy measurement of HRR is crucial for?re tests.The cone calorimeter was developed to measure HRR based on the principle of oxygen consumption and used in many international laboratories[17,18].The cone calorimeter can be regarded as a powerful tool for studying?re suppression of agents.

In this study,an attempt was made to develop an effective recycling technique for used polyurethane.Polyurethane was decomposed with TCPP(tri(2-chloropropyl)phosphate),TEP (triethyl phosphate),and TMP(trimethyl phosphate)to produce phosphorous containing?ame retardants.These degraded pro-ducts were characterized by NMR,FT-IR and were used as an addition agent to synthesize rigid polyurethane foam.The recycled polyurethane foams were compared with virgin polyurethane containing common?ame retardants on mechanical properties, cell morphology and thermal stability.Furthermore,heat release rate(HRR)of the foam was measured by cone calorimeter to evaluate?ame retardant properties of the recycled polyurethane foams with various amounts of DEP.

2.Experimental

2.1.Materials

Used polyurethane foams,based on pure MDI(diphenyl-methane diisocyanate),BASF,and polyester polyol prepared by adipic acid and diethylene glycol(DEG),were chosen for https://www.360docs.net/doc/fb7631882.html,mercial reagents of triethyl phosphate,trimethyl phosphonate,and tris(2-chloropropyl)phosphate were used with-out further puri?cation.

2.2.Chemical degradation of?exible polyurethane foam

The polyurethane foams were cut into small pieces and placed into a four necked?ask equipped with a mechanical stirrer, thermometer and re?ux condenser,then,triethyl phosphate was added into the glass apparatus.The weight ratio of polyurethane to triethyl phosphate was1–3.The degradation was proceeded at 1908C for6h and unreacted triethyl phosphate was removed under vacuum distillation.Additional degradation experiments were performed with trimethyl phosphonate,and tris(2-chlor-opropyl)phosphate following the procedure described above.

2.3.Preparation of recycled polyurethane foams with DEP

Rigid polyurethane foam was produced using the various amount (5,10,15and20wt%to polyol)of degraded products(DEP)as a ?ame retardant.Polyol and the additives were mixed and then stored at room temperature for24h.1.57pph(part per hundred of polyol in weight)of surfactant,0.46pph of amine catalyst,12pph of DEP and0.6pph of blowing agent such as distilled water or11.5pph of HFC-365mfc[hydro?uorocarbon(CF3CH2CH2CHF2)]were added according to100parts of polyol.After the mixed solution was added to the amounts of MDI corresponding to113of NCO index,the solution was stirred at3000rpm for30s to prepare the rigid polyurethane foam.In order to con?rm the?ame retardation of recycled polyurethane foams with DEP,pure polyurethane foam and polyurethane foam including general?ame retardant,phosphorus type?ame retardant,was prepared and analyzed in comparison with recycled polyurethane foam.

2.4.Characterization

The31P NMR spectra of the products(DEP)in CDCl3were determined using a Varian NMR-AS500spectrometer.Infrared spectra of the samples on a KBr pallets were obtained with a Jasco Fourier transform infrared spectroscopy(FT-IR)over the wave-numbers range from600to4000cmà1.The glass transition temperature of recycled polyurethane and pure polyurethane were determined by a differential scanning calorimeter(TA instrument) at a heating rate of208C/min and the nitrogen?ow rate of100ml/ min.Thermogravimetric analysis(TGA)was performed using a Perkin-Elmer instrument.The samples were heated from258C to 6008C at a heating rate of108C/min and the nitrogen?ow rate of 20ml/min.Scanning electronic micrographs of polyurethane foams were obtained on a JEOL-JSM6500F SEM after the specimens were sputter-coated with gold.Mechanical properties of recycled polyurethane and pure polyurethane were determined by uni-versal test machine.

2.5.Flame retardant property of polyurethane foams(?re resistance)

The in?ammability of prepared rigid polyurethane foams was evaluated by ASTM D1692.The polyurethane samples were cut into the dimension of150mm(L)?50mm(W)?13mm(T).The samples were on?re,then the time were counted until extinguished.The interval from ignition to extinguish of samples were measured.

2.6.Cone calorimetry

Several combustion parameters were determined using a cone calorimeter which is known to be able to provide useful information during combustion.

The parameters obtained from the cone calorimeter are listed below.

(1)Heat release rate(HRR)as function of time.

(2)Peak of heat rate release(PHRR),which is considered as a

parameter that best expresses the maximum intensity of a?re indicating the rate and extent of?re spread.

According to ISO5660-1[19],various combustion parameters were determined using a dual cone calorimeter(Fire Testing Technology).The measurement of heat released rate by the cone calorimeter does based on the oxygen consumption principles which the heat of about13.1MJ is radiated if the oxygen1kg is consumed among the combustion of organic materials[20].The oxygen consumed induced from the oxygen content in the burnt gas?ow and?ow rate was measured and it evaluated when the specimen exposed to the radiant heat in which it sets up was ignited.The heat release amount due to the combustion of a material and per square is calculated by Eqs.(1)and(2):

qetT?

Dh c

r O

e1:10TC

???????

DP

T e

s

X0O2àX O2

1:105à1:5X O2

(1) q AetT?

qetT

s

(2)

q A(t)is the heat release rate per square meter,q(t)is the heat release rate,A s is the surface area of the sample,D h c is the pure heat of combustion,r O is the stoichiometry oxygen per fuel mass ratio,C is the oxygen consumption correction constant,D P is the pressure difference of ori?ce,T e is the absolute temperature of gas at ori?ce,X O2is the oxygen branch scale toward the molar fraction of the oxygen and X0O2is the initial value of oxygen analyzer.

The cone calorimeter is the dynamic method in which it supplies the air of the predetermined amount as the testing method that it actually most well tracing the topic condition and it can accurately evaluate the combustibility of the devices.

Y.-j.Chung et al./Journal of Industrial and Engineering Chemistry15(2009)888–893889

It performed according to ISO 5660-1.After 6mm specimen (100mm ?100mm ?6mm)is cut with a square and it maintains until a constant becomes to the temperature 238C,and the relative humidity 50?5%,the non-exposure side is surrounded with the aluminum foil.

The calorie of the cone heater revised a trial that the set value ?2%within,and the oxygen content of the oxygen analyzer became 20.95?0.01%and the discharge ?ux was set to 0.24?0.002m 3/s.

The heat release rate and combustion parameter from the sample are ignited with the time exposing to 50kW/m 2radiant heat with the state where it horizontally set up in the cone calorimeter and attaches the outside ignition for the moisture and when it is ignited.

3.Results and discussion 3.1.Chemical structure of DEP

Figs.1and 2show FT-IR spectra of pure polyurethane,degraded polyurethane oligomer (DEP)by TEP (triethyl phosphate)and recycled polyurethane which was synthesized with 20pph addition of degraded polyurethane oligomer (DEP).In the FT-IR spectrum of degraded polyurethane oligomer (DEP)by phosphoric ester,P 55O stretching vibration bands appeared at 1250cm à1which was not found at pure polyurethane (Fig.1).It seems that the degraded products of polyurethane (DEP)are phosphorous containing material.The –C 55O bands consist of hydrogen-bonded

–C 55O (1700cm à1

)and free –C 55O (1725cm à1)in pure polyur-ethane compound possibly due to secondary interactions of urethane and urea functional group in polyurethane with –NH,–OH group in each chains (Fig.2).The –NH stretching vibration bands in pure polyurethane seems to be affected by hydrogen bonding with polar –C 55O functional group since there is a broad

peak at 3400cm à1

.The –NH stretching vibration bands in the degraded polyurethane oligomer by TEP (triethyl phosphate)was not as broad and strong as the –NH bands in pure polyurethane.The –C 55O stretching bands was shown in single peak after polyurethane was degraded by phosphoric ester.It means that the bonds of N–H in PU chains were broken by TEP,then,hydrogen bonding between carbonyl group and –NH in urethane is disappeared.These results are consistent with the decomposition mechanism of polyurethane proposed by Troev who suggests that structures and molecular weights of the degraded polyurethane products could be variable [3–5].

Fig.3shows 31P NMR spectra of TEP (triethyl phosphate)and the decomposed polyurethane oligomer through the exchange reaction of waste polyurethane and TEP.Since the structure of TEP is symmetric along the axis of P 55O bond,all phosphorous seem to be under the same condition which gives single peak at 0.53ppm (Fig.3).The chemically decomposed polyurethane oligomer with

phosphorus compound has many peaks around à10to 2ppm in 31

P NMR spectrum (Fig.3).According to these results,it is proved that polyurethane chains are degraded by phosphoric ester to produce the phosphorous containing urethane oligomers.

3.2.Thermal stability and mechanical properties

Thermal degradation of virgin polyurethane and the recycled polyurethane foam were investigated by TGA under a nitrogen atmosphere at a heating rate 108C/min.The recycled polyurethane foam was prepared using the 10pph (part per hundred based of polyol)of degraded products (DEP)which was polyurethane oligomer decomposed by phosphoric ester such as TMP and TCPP.As shown in Fig.4,the recycled polyurethane foam with DEP degraded at the temperature 1–58C higher than the virgin polyurethane foam.After the recycled polyurethane foam with DEP-TMP which represents the PU oligomer decomposed by TMP,was degraded at 5908C,15%residues are remained.Also the recycled polyurethane with the DEP-TCPP which represents the polyurethane oligomer decomposed by TCPP degraded to give 10%residue at 5908C.While the virgin polyurethane foam was degraded to give only 4%residue at the same temperature.This suggests that the degraded polyurethane oligomer by TMP,TCPP can be acted as the effective ?ame retardants and the recycled polyurethane with DEP is more thermally stable polymeric materials than the virgin polyurethane foam.

Table 1shows the mechanical properties of the pure polyurethane foam,the polyurethane foam with ?ame retardants such as TEP,TMP,TCPP and the recycled polyurethane with

DEP.

Fig.1.FT-IR spectra of (a)polyurethane scrap and (b)degraded PU by

TEP.

Fig.2.FT-IR spectra of (a)polyurethane scrap,(b)degraded PU by TEP and (c)recycled PU with

DEP.

Fig.3.31P NMR spectrum of TEP and degraded polyurethane foam by triethyl phosphonate (DEP-TEP).

Y.-j.Chung et al./Journal of Industrial and Engineering Chemistry 15(2009)888–893

890

The mechanical properties such as compressive strength and density of recycled polyurethane foam with DEP showed similar to those of virgin PUF and PUF with the commercial ?ame retardants.However,tensile strength is increased up to 20%in the recycled polyurethane using DEP.We suggest that the increase in physical

properties of recycled PUF may be due to the miscibility of polyurethane chains and phosphorous containing polyurethane oligomers (DEP)which are similar chemical structures and then the interfacial strength of two materials would be improved.

PUFs are easily ignited,therefore,the ?ame-retarding agents such as TCPP,TEP,TMP was usually added into the commercial polyurethane foams with the amount of 10wt%based on the polyol.The polyurethane foam with the commercial ?ame-retarding agents and DEP showed self-extinguishing property within 30s.This means that the DEP could act as ?ame retardant in preparation of polymeric materials as like TCPP,TEP,and TMP.3.3.Cell morphology

The effect of DEP as ?ame retardants on the cell morphology of the recycled polyurethane foam was studied in comparison with virgin polyurethane foam and polyurethane foam with the commercial ?ame retardant,TCPP.Fig.5shows scanning electron micrographs of the virgin PUF (a),PUF with TCPP (b)and the recycled PUF with DEP (c).The micrograph of recycled PUF shows uniform cell morphology as virgin PUF and the PUF with TCPP.This

Table 1

Mechanical properties and glass transition temperature of polyurethane foam.

Compressive strength ekg f =cm 2T=density ekg =cm 2T

Tensile strength ekg f =cm 2T=density ekg =cm 2TT g (8C)

Virgin-PU 698458158PU–TEP 668780153PU–TMP 702781148PU–TCPP

689772143Recycled PU–TEP 585819139Recycled PU–TMP 649842144Recycled PU–TCPP

658

968

159

Fig.4.TGA thermograms:(a)virgin-PU,(b)recycled PU with DEP-TCPP and (c)recycled PU with

DEP-TMP.

Fig.5.Scanning electron micrographs of (a)PU foam,(b)PU-TCPP foam,and (c)recycled PU/DEP-TCPP

foam.

Fig.6.CO of polyurethane under a heat ?ux of 50kW/m 2.

Y.-j.Chung et al./Journal of Industrial and Engineering Chemistry 15(2009)888–893891

result might be due to the miscibility of DEP with polyurethane chains in the recycled PUF (Fig.5).3.4.Cone calorimeter

The heat release rate and combustion parameter experimental results about the polyurethane foam are shown in Table 2.Since being shown in 5–6s,the ?ame retardant is combined or in case of being added,the ignition time of the remainder PU foam is determined in comparison with an ignition time (time to ignition,TTI)4s of the pure polyurethane foam that the burning restraint function is given.

Heat release rate represents a quantity of heat generated per unit area and time.HRR represents a quantity of heat generated per unit area and time.When a sample is ignited,heat is generated depending upon its ?ammability.PHRR is one of the important index which one can presume the extent of ?re.

Since being shown in 330.52kW/m 2,the peak heat release rate (PHRR)of the TCPP/PU in which the ?ame retardant is contained in comparison with the peak heat release rate (PHRR)360.70kW/m 2of the pure polyurethane foam in which the ?ame retardant does not become with addition is determined that the burning restraint effect is excellent and the peak heat release rate reduces (Table 2,Fig.8).

In the case of the TCPP/PU,rather the maximum heat release rate was higher in 362.15kW/m 2.It is determined that TCPP could not exhibit the effect that it is great about the combustibility suppress as the case of just mixing TCPP with PU.

And in case of processing with the DEP-TEP/PU and DEP-TMP/PU,for the peak heat release rate just having as 364.43kW/m 2,378.65kW/m 2and con?rming the burning restraint effect,it was insuf?cient.

That is,a peak heat release rate is determined that the quantitative evaluation has more to get accomplished in con-sideration of the total combustion time since being de?ned as the size of the instantaneously calorie in which it is generated with the surface of sample.

THR,total heat released by combustion,is a function of time per unit area and it is calculated by the integration of heat release for given time.

As shown in Table 2and Figs.6and 9,the THR value of the DEP-TEP/PU (10.0MJ/m 2)and DEP-TMP/PU (10.0MJ/m 2)is lower than the THR of the pure polyurethane foam (12.2MJ/m 2).

Particularly,in the case of the DEP-TCPP/PU (9.5MJ/m 2),we look at that THR is small and the burning restraint effect is excellent.

In the case of the TCPP/PU,it seems to do a role according to a situation even in case the THR just mixes the ?ame retardant with the polyurethanes as 9.5MJ/m 2.

In comparison with the pure polyurethane foam,the poly-urethane foam which is added ?ame retardant or DEP becomes reduced the average output of the CO 2gas except the DEP-TEP/PU.The average output of the CO gas increased with the TCPP/PU,DEP-TEP/PU,DEP-TMP/PU,and DEP-TCCP/PU (Table 2).

It shows that the incomplete combustion rate increased due to the ?ame retardant addition CO and CO 2were generated in the time slot when it is faster than an other in the case of the virgin PUF in which it does not ?ame retardant treatments after ignition of sample (Figs.6and 7).Flame retardant added test pieces lately generated CO and CO 2especially,the DEP-TCPP/PU foam most lately generated CO and CO 2(Figs.6and 7).Relatively the generation of CO of ?ame retardant added PU is faster than virgin-PU in the ?xed time slot (Fig.6).

Generation speed of CO which the ?ame retardant added PU showed the highness with the DEP-TMP/PU >TCPP/PU >DEP-TEP/PU >DEP-TCPP >PU.Increase of CO generation speed of PU

Table 2

Combustion parameters of polyurethane foams.Sample

TTI a (s)PHHR b (kW/m 2)THR c (MJ/m 2)CO mean (kg/kg)CO 2mean (kg/kg)CO/CO 2PU

4360.7012.20.0440 1.800.023TCPP/PU

6362.159.50.0854 1.760.048Recycled DEP-TEP/PU 5364.4310.00.0953 1.840.051Recycled DEP-TMP/PU 5378.6510.00.0703 1.330.052Recycled DEP-TCPP/PU

6

330.52

9.8

0.0846

1.75

0.048

a Time to ignition.

b Peak heat release rate.c

Total heat

released.

Fig.7.CO 2of polyurethane under a heat ?ux of 50kW/m 2

.

Fig.8.HRR of polyurethane under a heat ?ux of 50kW/m 2

.

Fig.9.THR of polyurethane under a heat ?ux of 50kW/m 2.

Y.-j.Chung et al./Journal of Industrial and Engineering Chemistry 15(2009)888–893

892

containing ?ame retardants is from incomplete combustion due to ?ame retardants (Fig.10).

We can know as this kind of in the generation speed of CO 2,moreover,the ?ame retardant treatments test piece relatively being small in the time slot when the generation speed is ?xed in comparison with the virgin-PU foam (Fig.11).

It is determined that if the ?ame retardant treatments are processed,the combustion control function is carrying out.4.Conclusions

Used polyurethane foam was chemically degraded by the treatment with ?ame retardants such as TCPP,TEP and TMP.The structure of degraded products (DEP)was turned out to be phosphorus-containing oligourethanes by the results from FT-IR and 31P NMR.Rigid polyurethane foam was produced using the degraded products (DEP)as ?ame retardants.The rigid Polyur-

ethane foam is called as recycled PU.Mechanical strength of recycled polyurethane shows as high as that of virgin polyur-ethane.

From the results of cone calorimeter and TGA,the recycled polyurethane shows reduced ?ammability and higher thermal stability over virgin polyurethane.In order to evaluate ?ame retardant properties of the polyurethane foams recycled by various phosphorus compounds,heat release rate (HRR)of the foam was measured by cone calorimeter.Among DEPs,DEP-TCPP which is the degraded polyurethane products by TCPP seems to be the most effective ?ame retardant in preparation of polyurethane foams.Increase of CO/CO 2ratio of PU containing ?ame retardants is from incomplete combustion due to ?ame retardants.Scanning electron micrograph of recycled PU reveals uniform cell morphology as virgin-PU.

Acknowledgements

The work was carried out with ?nancial support from the 2007Kyonggi University specialization program and by the special fund of disaster prevention’s priority of Kangwon National University in 2005.References

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Fig.10.CO production rate of polyurethane under a heat ?ux of 50kW/m 2

.

Fig.11.CO 2production rate of polyurethane under a heat ?ux of 50kW/m 2

.

Y.-j.Chung et al./Journal of Industrial and Engineering Chemistry 15(2009)888–893893