Marianne Guillemot
email: marianne.guillemot@inrs.fr

Benoît Oury
email: benoit.oury@inrs.fr

Sandrine Melin
email: sandrine.melin@inrs.fr

Identifying thermal breakdown products of thermoplastics

Keywords: Identifying thermal breakdown products of thermoplastics Plastic thermal degradation, analytical protocol, contaminant in plastic molding shops

published or not. The documents may come

INTRODUCTION

Plastics form a major part of our living environment because of their application potential and adaptability. They are the basic materials of many products in multiple areas such as agriculture, healthcare, energy generation, aerospace, automotive, maritime, construction, electronics, packaging or textile. In Europe, this activity is undertaken by 1.45 million people working at more than 60,000 companies (1) .

Main chemical exposure routes for employees in the workplace include dermal contact and via the respiratory system by inhalation of dust and volatile compounds released by polymers during thermal processing [START_REF] Rosenberg | Allergic occupational respiratory disorders in the plastics industry. Occupational allergology-pneumology sheet TR 46[END_REF] . The plastic material choice and the thermal process implemented depend on the type of article, its size and the physical properties that are required for its use. During production of plastic articles, polymers are subjected to temperatures between 150 °C and 450 °C. These thermal processes can lead to emission of toxic VOCs in plastic molding shops [START_REF] Lafon | Toxicity of thermal degradation products of plastics[END_REF] . In addition to exposure during normal production operations, workers can be exposed to toxic compounds during operations that may cause serious overheating of the material such as drilling, abrading, cutting or welding operations as well as during process malfunctions and breakdowns. Plastics overheating can lead to the release of thermal breakdown products in much higher concentrations or of different type than during normal production.

In general, polymer heating causes release of free monomers and decomposition of polymers or their additives; this has been reported in several studies [START_REF] Forrest | Emission from processing thermoplastics[END_REF] .Our knowledge of occupational exposure to toxic compounds during thermal processing of plastics is limited as most of the studies are focused on a thermoplastics or pollutants family [START_REF] Farhi | Plastics and additives-Health and safety[END_REF][START_REF] Mairesse | Thermal degradation products of plastics[END_REF][START_REF] Masson | Thermal degradation of polymers[END_REF] or conducted to determine plastics thermal behaviour [START_REF] Price | Degradation of polymers studied by mass spectrometry[END_REF] . Numerous studies have been carried out on thermoplastic decomposition in an inert atmosphere (nitrogen or helium) [START_REF] Unwin | Airborne emissions of carcinogens and respiratory processing of plastics[END_REF] in order to determine thermoplastic composition or assess thermoplastic ageing pathways. However, little is known of the degradation products released under real thermal processing conditions and in the presence of air, which can lead to the formation of oxygenated decomposition byproducts such as aldehydes, ketones or alcohols [START_REF] Wampler | Applied pyrolysis handbook[END_REF] . Besides, K. Yamashita et al. have observed that during polymer degradation, smaller amounts of VOCs were emitted under nitrogen atmosphere than under air atmosphere [START_REF] Yamashita | Compositions of volatile organic compounds emitted from melted virgin and waste plastics pellets[END_REF] .

The difficulty with such an assessment resides in the wide variety of plastics, additives and processes used. Worker exposure assessment requires knowledge of the type of thermal degradation products, which depend on polymer type and temperature implementation.

Moreover, there is no recognized, standardized method of thermal degradation of plastics for representatively determining the thermal degradation products, to which workers may be exposed in plastic production shops.

The purpose of this study was therefore twofold. The first objective was to develop a thermal degradation protocol representative of industrial thermal processing and applicable to many thermoplastics. To achieve this goal, several degradation conditions were studied and the defined protocol was validated by atmospheric measurements during industrial thermal processing. The second objective was to define, from the developed protocol, thermal decomposition products for the most commonly used polymers and temperatures in order to develop a diagnostic tool for improving worker exposure assessment.

METHODS AND MATERIALS

We chose to study the most widely used thermoplastics. Table I shows the polymer families studied as well as the corresponding polymer consumption in Europe and the industrial processes used during the field survey. 15 of the 25 thermoplastics were studied both in the laboratory and the factory. The polymers with no process type reported were only studied in the laboratory.

Laboratory analysis

Conditions for thermoplastic thermal decomposition were chosen as close as possible to those under which real industrial processes are performed. Not all industrial processing conditions can be reproduced in the laboratory. In real life, thermoplastics are heated in an endless screw under high pressure before injection in a mould or extrusion threw the die of the extruder. Melt thermoplastics are maintained at high temperature under air atmosphere for several minutes. Two methods were selected thanks to their ability to subject polymers to heating conditions close to those encountered in many real situations (12)(13)(14) : thermogravimetric analysis (TGA) and pyrolysis under airflow. Both these methods allow thermal breakdown in air, controlled temperature with slow or fast heating rate and steps at constant temperature.

Thermogravimetric analyses were performed on a TA Instruments Q50 analyser under 90 ml/min airflow. A piece of thermoplastic (with a mass of several micrograms) was placed on a platinum pan in the analyser oven. The heating rate could be varied from 5 °C/min to 50 °C/min. Weight loss was monitoring during heating so that the onset degradation temperature (Ti), the temperature at maximum weight loss (Tmax) and the final weight loss could be determined (15)(16)(17) . Released compounds were sampled at ambient temperature using convenient samplers connected to the outlet of the thermogravimetric analyser oven. Multibed sorbent tubes (Carbotrap 300) were used for qualitative analysis purposes as described in the National Institute for Occupational Safety and Health (NIOSH) method 2549 (18) . Multibed tubes were then analysed off-line by thermal desorption (Perkin Elmer ATD50). Inlet split and outlet flow was respectively of 40 ml/min and 50 ml/min. The desorption flow was of 10 ml/min. The multi-bed sorbent tubes was desorb at 320 °C during 20 min. The cold trap was an air toxic trap, maintained at -30 °C during desorption and then heated at 330 °C during injection in a GC/MS analyser (Perkin Elmer).

Pyrolysis-in-air analyses were performed using a CDS Analytical Pyroprobe 5200 connected on-line to a GC/MS analyser. During pyrolysis, released products were collected on a cold trap filled with Tenax and maintained at -30 °C under liquid nitrogen flow. At the end of decomposition, the trap was flushed with helium and heated very quickly to 280 °C to inject the adsorbed compounds into the split/splitless injector of the GC maintained at 270 °C with a split ratio of 100. This method does not allow quantitative analysis, but does allow degradation involving several temperature steps. Table II summarises all the features of each technology.

Thermal breakdown products were analysed using a semi-polar capillary column (vf-624ms, 0.32mm*1.4µm*60m) with a column flow of 1 ml/min. The oven programming was 35 °C for 5 minutes, 250 °C for 15 minutes with a heating rate of 5 °C/min.

To determine influencing factors on released thermal breakdown products, three parameters were studied: the sample preparation methodsmanual cutting, ambient or cold grindingthe heating rate during thermal degradation -5, 10 20 and 50°C/minand the decomposition methodthermogravimetric analysis and pyrolysis. All these experiments were performed under airflow of 90 mL/min. To develop the protocol, the influence of the three parameters was evaluated comparing the thermal breakdown compounds obtained for each experiment. For each reference of thermoplastics, laboratory experiments were replicated between 4 and 13 times.

Industrial processing

Data obtained in the laboratory were compared to those collected in 13 thermoplastic processing shops selected to provide a wide range of polymers and processes. Thus, 15 of the 25 polymers were studied in both the laboratory and the factory (Table I).

Various processes were encountered at the 13 industrial sites: 16 extrusion lines for continuous production of tubing, cables and films on 4 sites; 50 injection-molding presses for production of car components, connections and packing on 8 sites, hot wire film cutting on 2 sites, laser cutting on 2 sites, and automatic and manual welding on 3 sites.

Both sampling at the processes emission area and individual monitoring were performed.

In the first case, sampling devices were placed as close as possible to the emission location (about 30 cm) to identify and quantify compounds released in air during the heating process.

Personal monitoring was carried out on operators during normal operating conditions, during purging operations and laser cutting operations. For screening identification by NIOSH method 2549 (16) , the collection device used was a thermal desorption tube filled with three adsorbent media that allowed collection of C 3 to C 30 molecules. For quantifying airborne concentrations, the sampling and analytical methods listed in Table III were used.

Polymer pellet samples were simultaneously collected at the process feed side to compare the atmospheric measurements with the results obtained by thermal decomposition in the laboratory for the relevant polymer.

RESULTS AND DISCUSSION

The onset degradation temperature (Ti), the temperature at maximum weight loss (Tmax) and the final weight loss were determined as illustrated in Figure 1.

Laboratory analysis -Parameter optimisation

This survey studied the influence of three parameters on thermal decomposition product characteristics.

Thermogravimetric analysis-based thermal degradation was undertaken on three thermoplastics (polyethylene (PE), polyacrylonitrile-butadiene-styrene (ABS) and poly(styrene/acrylonitrile) (SAN)) subjected to an airflow of 90 ml/min and a heating rate of 20°C/min up to 450 °C in order to compare different sample preparation methods.

The main products proved to be the same whatever the preparation method (manual cutting, ambient or cold grinding), specifically C 1 -C 5 aldehydes for PE, styrene, benzaldehyde, acrylonitrile and alpha-methylstyrene for ABS and styrene, benzaldehyde, alpha-methylstyrene and acrylonitrile for SAN.

Among the preparation methods tested, cold grinding gave more homogenous samples than ambient grinding and the former preparation method is safer for the analyst.

Heating rate influence was assessed by varying the temperature gradient between 5 and 50 °C/min. Polyethylene (PE) and polypropylene (PP) decomposition was performed by thermogravimetric analysis under an airflow of 90 ml/min. The final temperature was 450 °C.

PE thermal breakdown at 10 °C/min, 20 °C/min and 50 °C/min caused emission of C 1 -C 5 aldehydes, propane and methylvinylketone. At 5 °C/min, the detected products were C 1 -C 3 aldehydes, C 3 -C 4 alkanes, methylvinylketone and acetic acid.

In the case of PP, acetaldehyde, C 3 , C 5 , C 8 , C 9 ketones and acetic acid were observed at 10 °C/min, 20 °C/min and 50 °C/min. No C 5 ketone was detected at 5 °C/min. We therefore conclude that the same compounds are obtained with a heating rate of 10, 20 and 50 °C/min.

Only the products obtained at 5 °C/min differ, probably due to the lower energy supply. The 20 °C/min heating rate offers the best compromise between the technical properties of the analyser oven and a short-time analysis.

The third parameter evaluated was the thermal degradation method. Compounds obtained from decomposing 21 thermoplastics by pyrolysis and thermogravimetric analysis in air were compared. The thermoplastic samples were decomposed with a heating rate of 20 °C/min up to 450 °C. The released compounds was analysed by GC/MS. Only the method of sampling the released compounds differed in the two methods. Figure 2 shows typical results. The main decomposition compounds are identical; only the response observed for each compound differs according to the degradation method used.

The data obtained allowed us to select the best protocol. TGA and pyrolysis in air both enable qualitative determination of thermal decomposition products, either by off-line analysis of screening samplers or by on-line analysis. However, only thermogravimetric analysis enables determination of the initial decomposition temperature and weight loss at a determined temperature.

The selected protocol therefore takes advantage of each method:

-Cold grinding, thermal breakdown by thermogravimetric analysis in air up to 450 °C with a 20 °C/min heating rate: monitoring of the polymer weight loss with temperature and quantitative analyses of toxics compounds such as aldehydes, aromatic compounds and acrylates on the appropriate samplers -Cold grinding, thermal breakdown by pyrolysis in air with a 20 °C/min heating rate: qualitative determination of decomposition compounds released by the polymer at the process temperature and at 450 °C.

Laboratory analysis -Thermal degradation products

The products of thermal decomposition in air and weight loss were determined using the selected protocol for each of the 25 thermoplastics studied. The results obtained from pyrolysis in air of all the polymers were classified by chemical compound family as illustrated in Figure III. These results highlight the fact that the main decomposition products are free monomers, monomers from polymer cracking, oxygenated compounds from polymer groups and products of oxidative reactions (19) . Observed degradation compounds can vary from a polymer reference to another from the same family, depending on the additive type and content. In parallel, the weight loss of the 25 polymers was monitored by TGA under the chosen conditions (20 °C/min, 450 °C, in air, see Table IV). In the case of the 8 references of PP, the results reveal that thermal behaviour of the same thermoplastic can vary depending on the additives and the type and rate of mineral loading (Table IV). For example, PP-4 and PP-5 which are respectively filled with 30 and 70% of mineral compounds, only loss 60 and 30% of their initial weight at 450°C, while the other references loss between 90 and 97% of their initial weight. The weight loss corresponds to the degradation of the polypropylene contains in PP-4 and PP-5, therefore these two references are less emissive thank to their higher mineral loading.

Industry measurements -Protocol validation

527 atmospheric and 71 polymer samples were taken on 13 industrial sites.

Table V shows the results obtained. Thermal degradations were conducted in the laboratory based on the selected protocol and at the same temperature as in the industrial process to validate protocol representativeness. Results obtained by laboratory analysis and by measurements taken in workplace situations are in fact in fairly close agreement. Some plastics (e.g. polycarbonate (PC) and thermoplastic polyurethane (TPU)) did not decompose at the temperature applied in the laboratory. These results are consistent with thermogravimetric analyses (Table IV) showing that no degradation occurs below 390 °C and 250 °C for PC and TPU respectively. Thus, the air pollutants detected on the samplers must have originated from adjacent processes or other unrelated activities. This could also have been the case when compounds were detected on the industrial premises but not in the laboratory.

Table VI shows concentration levels of hazardous substances emitted at various industrial processes. Most of the time, concentration levels of toxic compounds released from the processes under study were low. Most operators control temperature carefully to prevent thermoplastic degradation and this practice has a positive impact on emission levels. The formaldehyde and benzene emissions are detailed in Table VII, depending on the production process and the temperature of plastic transformation. The results show that injection-molding of POM can generate high formaldehyde emissions. Under normal operating conditions -at temperatures between 200 and 215°C-formaldehyde levels varied from 0.32 to 0.44 mg/m 3 at about 30 cm of the heating zone of POM. During the purging step, when the polymer is flushed out of the press at 215°C, the formaldehyde concentration was of 10 mg/m 3 at 30 cm of the injection-molding furnace. The purge of the press requires the intervention of an operator. The personal samplings made during this step exhibit a formaldehyde concentration of 1.12 mg/m 3 during 15 minutes. Therefore, even at temperatures below the initial decomposition temperature, which is 254°C for POM (Table III), this polymer releases formaldehyde, most probably corresponding to non-polymerized monomer molecules.

Laser cutting of PMMA appears to be another source of formaldehyde emissions. In the laser cutting cabin, concentrations of formaldehyde vary from 0.34 to 0.53 mg/m 3 . Laser cutting of PMMA also generates high concentrations of methyl methacrylate, up to 37 mg/m 3 at about 30 cm of the laser. The large amount of energy supplied by the laser causes the thermal degradation of the PMMA to its monomer. The personal samplings carried out for 4 hours on the operator working at the laser cutting station measured formaldehyde and methyl methacrylate concentrations of 0.04 and 0.5 mg/m 3 respectively.

Benzene concentration was also measured in the visited plastic production shops. Levels were mostly less than 0.1 mg/m 3 . Concentrations between 0.18 to 0.32 mg/m 3 were obtained in the case of injection-molding of PET and POM and during PMMA transformation by laser cutting.

Due to the high temperatures involved, this process has the greatest potential to generate harmful substances. Therefore, to prevent workers exposure to thermal breakdown products released by laser cutting, it would be necessary to equip the station of a localized collection system to capture the different pollutants generated at the emission source.

As shown in Table VII, formaldehyde and benzene emissions were detected in the laboratory study for the same thermoplastic/temperature combination except for very low level and in the cases of PET and POM transformation. Further analyses had shown that the emission source of benzene in these cases was the vacuum pump of the injection-molding press and not directly the thermal processing of the thermoplastics.

CONCLUSION

The laboratory study of the influence of thermal breakdown parameters allowed us to establish a decomposition and analytical protocol.

Comparison of emissions measured during real industrial processing and when applying the laboratory protocol to the same thermoplastic samples provided similar results.

Thermal breakdown product characteristics and temperature behaviour were determined for the 25 thermoplastics studied.

These combined data effectively contribute to prevention on two sides:

-Thermal degradation control by knowing the degradation onset temperature -Workplace exposure assessment at thermoplastic production facilities: the protocol is a tool available to prevention personnel for assessing the toxic compounds likely to be released by thermal processing of plastics 12. Prati, S., S. Smith, and G. Chiavari: Characterisation of siccative oils, resins and pigments in art works by thermochemolysis coupled to thermal desorption and pyrolysis GC and GC-MS. Chromatographia 59 (3-4): 227-231 (2004).

8

  different samples of PP (named PP-a to PP-h), and 2 different samples of ABS (named ABS-a and ABS-b) and PS (named PS-a and PS-b) were studied. They were supplied by different manufacturers and they differ by their additives type or content and their rate or nature of mineral loading.

13.

  Bower, N.W., and C.J.K. Blanchet: Analytical pyrolysis -Chromatography: something old, something new. J. Chem. Educ. 87:467-469 (2010). 14. Bhaskar, T., J. Kaneko, A. Muto, Y. Sakata, E. Jakab, T. Matsui, and M.A. Uddin: Pyrolysis studies of PP/PE/PS/PVC/HIPS-Br plastics mixed with PET and dehalogenation (Br, Cl) of the liquid products. J. Anal Appl. Pyrol. 72:27-33 (2004). 15. Blazek, J.: "Study of the reaction kinetics of the thermal degradation of polymer." PhD diss, Institut National Polytechnique de Toulouse, University of Toulouse, 2005. 16. Conesa, J.A., A. Marcilla, R. Font, and J.A. Caballero: Thermogravimetric studies on the thermal decomposition of polyethylene. J. Anal Appl. Pyrol. 36: 1-15 (1996). 17. Cervantes-Uc, J.M., J.V. Cauich-Rodriguez, W.A. Herrera-Kao, H. Vázquez-Torres, and A. Marcos-Fernández: Thermal degradation behavior of polymethacrylates containing amine side groups. Polym. Degrad. Stabil. 93:1891-1900 (2008). 18. Method 2549 of Niosh Manual of Analytical methods, Fourth Edition, 5/16/96. 19. Cervantes-Uc, J.M., J.V. Cauich-Rodriguez, H. Vázquez-Torres, and A. Licea-Claverie: TGA/FTIR study on thermal degradation of polymethacrylates containing carboxylic groups. Polym. Degrad. Stabil. 91:3312-3321 (2006).

Figure 1 .Figure 2 .Figure 3 .

 123 Figure 1. Thermogram interpretation. Ti: onset degradation temperature; Tmax: temperature of maximum weight loss

Table I .

 I Polymer, name, abbreviation, % European consumption (*) and processes implemented during atmospheric measurements at plastic transformation facilities (polymers with no process reported were only studied in the laboratory)

	Polymer	Name	Abbreviation Cons. % * Process
					Extrusion
		Polyethylene	PE	29%	Injection-moulding Welding
	Polyolefins				Hot wire cutting
					Extrusion
		Polypropylene	PP	19%	Injection-moulding
					Welding
					Extrusion
	Polyvinylic	Polyvinylchloride	PVC	11%	Injection-moulding
					Welding
		Poly-vinylidene-chloride	PVDC	1%	-
		Polystyrene	PS	7.5%	Injection-moulding
	Polystyrenic	Poly(styrene/acrylonitrile) Poly(styrene/Butadiene) Polyacrylonitrile-butadiene-styrene	SAN SB ABS	2%	--Injection-moulding
		Poly(styrene/ethylene/butylene)	SEBS		Injection-moulding
	Polyacrylic	Polymethylmethacrylate	PMMA	1%	Injection-moulding Laser-cutting
		Polyacrylonitrile	PAN		-
	Polyacetal	Polyoxymethylene	POM	0.5%	Injection-moulding
		Polyamide 6	PA 6		Extrusion
	Polyamides	Polyamide 12 Polyamide 6.6	PA 12 PA 6.6	3%	-Injection-moulding Extrusion
	Polycarbonates		PC	1.3%	Injection-moulding Extrusion
					Injection-moulding
		Polyethylene terephthalate	PET		Extrusion
	Linear polyesters			7%	Hot wire cutting
		Polybuthylene terephthalate	PBT		Injection-moulding
		Polytrimethylene terephthalate	PTT		-
	Cellulosiques	Acetobutyrate cellulose	CAB	<0.5%	-
		Polyvinylidene fluoride	PVDF		-
	Polyfluoroethene	Polytetrafluoroethylene	PTFE	<0.5%	-
		Ethylene-Tetrafluoroethylene	ETFE		Extrusion
	Thermoplastic polyurethane	TPU	7%	Parboiling
	Other	Styrene acrylic copolymer	NAS	<0.5%	-

Table II .

 II Summary of thermogravimetric analysis and pyrolysis characteristics

		TGA	Pyrolysis
	Atmosphere	Oxidative or neutral	Oxidative or neutral
	Heating rate	5 to 50 °C/min	Up to 1000 °C/sec
	Analytical coupling	Delayed GC/MS analysis	Online thermal desorption of the cold trap and GC/MS analysis
	Sampling mode of	At the outlet on sampling media	On integrated cold trap of
	released compounds	at ambient temperature	Tenax at -30 °C
	Weight loss	yes	no
	Several temperature steps	no	yes

Table IV :

 IV Initial decomposition temperature (Ti), temperature of maximal weight loss (Tmax), mean and variance of final weight loss, number of replicates (number of experiments carried out for each reference) for the 23 thermoplastics studied

	Polymers	Ti (°C)	Tmax 1 (°C) Tmax 2 (°C)	Final weight loss (%) mean Variance	Replicas
	PE	274	391	435	90	1.81	11
	PP-1	258	363	NA	92	3.19	4
	PP-2	262	374	NA	93	0.40	5
	PP-3	248	291	NA	95	4.25	4
	PP-4	201	290	420	59	4.92	6
	PP-5	290	375	NA	30	7.89	6
	PP-6	260	368	438	92	10.16	5
	PP-7	248	290	NA	97	23.19	4
	PP-8	247	286	NA	97	8.19	4
	PVC	260	317	446	63	5.51	7
	PVDC	210	278	NA	73	19.76	5
	PS-1	257	341	NA	96	8.64	5
	PS-2	239	382	427	95	13.88	9
	PS-3	244	334	NA	96	21.00	6
	SAN	258	392	NA	95	3.88	13
	SB	308	439	NA	82	NA	4
	ABS-1	285	424	NA	90	7.56	10
	ABS-2	271	422	NA	77	8.50	4
	PMMA	286	351	NA	96	15.93	13
	PAN	299	343	NA	27	NA	2
	POM	254	294	NA	99	6.36	8
	PA 6	318	440	NA	78	NA	2
	PA 6,6	304	444	NA	70	NA	2
	PA 12	238	446	NA	73	NA	2
	PC	391	NA	NA	22	NA	3
	PET	313	442	NA	83	17.69	4
	PBT	302	416	NA	94	NA	2
	PTT	301	416	447	85	NA	2
	CAB	144	380	NA	94	NA	2
	PVDF	408	NA	NA	38	10.69	4
	PTFE	NA	NA	NA	0	NA	4
	TPU	254	283	348	83	NA	2
	NAS	274	391	435	90	1.81	11

Table V .

 V Thermal decomposition products identified from atmospheric samples taken on industrial sites and laboratory-based degradations

	Polym er	On industrial processes	In laboratory
	Tem

perature of the industrial process Laboratory degradation tem perature Main product only find on industrial site Main product only find in laboratory

		Identified therm al degradation products
		Main com m on product
		Minor common product
		Minor product only find on industrial site	Minor product only find in laboratory
	PE	170-200°C	180-200°C
		Aldehydes (formaldehyde, acetaldehyde)
		Acetic acid
		C 8 -C 16 saturated hydrocarbons
		C 3 aldehyde
		Alcohols (ethanol, ethoxypropanol)
		Furane
	PP	200-285°C	200-285°C
		C 3 -C 15 saturated hydrocarbons
		Aldehydes (formaldehyde, acetaldehyde, C 3 -C 7 )
		Ketones (acetone, butanone)
		Alcohols (methanol, ethanol, butanol)
		Acetic acid
		Furane
		Benzoic acid	Propanoic acid
		Tetrahydrofurane	Dimethylfurane
	PVC	180-215°C et 380°C	180-210°C et 450°C
		Aldehydes (formaldehyde, acetaldehyde)
		Methyl methacrylate
		Acetic acid
		C 3 -C 5 saturated hydrocarbons
		Ketones (methylethylcetone, methylvinylcetone)	hydrogen chloride
		Alcohols ( ethanol, ethyhexanol)	Aromatic hydrocarbons (benzene, toluene, styrene)
		C 6 -C 13 saturated hydrocarbons
	PS	210-230°C	230°C
		Arom atic hydrocarbons (styrene, ethylbenzene)
		Aldehydes (acetaldehyde, benzaldehyde)
		C 3 -C 16 saturated hydrocarbons	Acrylaldehyde
			Acetophenone
	ABS	230-305°C	230-305°C
		Arom atic hydrocarbons (styrene, benzene, toluene, m ethylstyrene)
		Aldehydes (formaldehyde, acetaldehyde)
		alcohols (methanol, ethanol, propanol)
		C 3 -C 9 saturated hydrocarbons
		Brominated compounds
			Isocyanonaphtalene
			Acrylaldehyde, benzaldehyde
			Phenol, cresol
			C 10 -C 13 saturated hydrocarbons
	SEBS	240-340°C	240-340°C
		Hydrocarbures arom atiques (styrene, benzene)
		Aldehydes (formaldehyde, acetaldehyde, benzaldehyde)
		C 3 -C 9 saturated hydrocarbons
		acetic acid
		alcohols (methanol, ethanol)	Toluene
			Propanoic acid and butanoic acid
			C 3 -C 9 ketones
	PMMA	240-260°C	240-260°C
		Methyl m ethacrylate, acrylate de m ethyle
		Aldehydes (form aldehyde, acetaldehyde)
		alcohols (methanol, ethanol)
		C 3 -C 5 insaturated hydrocarbons
		Benzaldehyde	Acrylaldehyde
		Styrene	C 8 and C 16 alcohols
		C 3 -C 5 saturated hydrocarbons	C 6 -C 12 insaturated hydrocarbons
			Methyl esters
			Methacrylonitrile, isobutyronitrile
	POM	190-215°C	190-215°C
		Aldehydes (form aldehyde, acetaldehyde)
		Alcohols (methanol, ethanol)
		Acetic acid
		Methylal	Isopropanol
		Phenylmethanol	Ketones (acetone, cyclohexanone)
		Methyl esters

Polym er On industrial processes In laboratory Tem perature of the industrial process Laboratory degradation tem perature Main product only find on industrial site Main product only find in laboratory

  Minor product only find on industrial site Minor product only find in laboratoryProducts in green text were found in both the field and laboratory studies

		Identified therm al degradation products
		Main com m on product
		Minor common product
	PA 6	270°C	270°C
		Caprolactam e
		Acetaldehyde
		C 4 -C 9 ketones
		Methacrylaldehyde
		Ethanol
		Acetic acid
		C 3 -C 9 saturated hydrocarbons
	PA 6.6	250-350°C	280-340°C
		Caprolactam e
		Alcohols (methanol, ethanol, propanol, butanol)
		Ketones (acetone, cyclopentanone)
		Aromatic hydrocarbons (benzene, toluene)
		C 3 -C 13 saturated hydrocarbons
		Acetaldehyde	Aldehydes (form aldehyde, acrylaldehyde, C 11 -C 14 )
		Insaturated hydrocarbons (C 4 -C 19 )	Cyclohexanone
		N-butylbenzensulfonamide	Acetic acid
		Butyle acetate	Acrylonitrile
			Dihydrofurane
	PC	250-320°C	250-320°C
		Acetaldehyde
		C 3 -C 4 ketones
		alcohols (ethanol, phenol, methoxypropanol)	Chlorinated compounds (traces)
		Methyl methacrylate
		Aromatic hydrocarbons (toluene, methylstyrene)
		Benzofurane, hydroxyacetophenone
		C 3 -C 14 saturated hydrocarbons
	PET	190-285°C	285°C
		Furane, tetrahydrofurane
		Aldehydes (formaldehyde, acetaldehyde)
		Alcohols (methanol, ethanol)
		Benzaldehyde
		Propanol, benzyl alcohol	Butanol
		Aromatic hydrocarbons (benzene, toluene,	Acetic acid
		monoterpenes )	Ketones (acetone, cyclohexanone)
		C 3 -C 10 saturated hydrocarbons	C 3 -C 4 insaturated hydrocarbons
	PC/PBT	215-260°C	260°C
		Methyl m ethacrylate
		Siloxanes
		C 3 -C 16 saturated hydrocarbons	Aldehydes (acetaldehyde, acrylaldehyde)
		Ethyl acetate, butyl acetate
	ETFE	320°C	320°C
		Tridecafluorohexane
		Saturated and insaturated fluorinated hydrocarbons
		Hydrogen fluoride
	TPU	160°C (TPU solution)	160°C (TPU alone)
		Acetaldehyde	Acetic acid (traces)
		Alcohols (methanol, ethanol)	Tetrahydrofurane (traces)
		Limonene
		C 3 -C 5 saturated hydrocarbons

Table VI .

 VI Concentration levels of hazardous substances emitted at various industrial processes.

				Airborne concentration of detected compounds (mg/m 3 ) a			WEL
	Compound	PE	PP	PVC	PA 6.6	ABS	PC	PET	POM	PS	PMMA	(mg/m 3 ) 8h/15min
	Formaldehyde	0.01 to 0.33	<0.01 to 0.19 (18)	0.01 to 0.23 (11)	<0.01 to 0.10 (9)	0.01 to 0.02 (8)	0.01 to 0.03 (3)	0.01 to 1.98 (18)	0.10 to 10.30 (11)	0.02 (2)	<0.01 (8) to 0.53	0.625/1.25
	Acetaldehyde	0.03 to 0.35 (20)	0.01 to 0.20 (18)	<0.01 to 0.08 (11)	0.01 to 0.03 (9)	<0.01 (8)	<0.01 (3)	0.09 to 1.94 (18)	0.01 to 0.57 (11)	0.009 (2)	0.02 to 0.04 (8)