**6. Degradation by kneading**

#### **6.1 Samples preparation**

By the reason of finding degradation mechanism of plasticized PVB, this material was reprocessed by kneading, rolling and pressing. Both dry (0.5 % water) and wet (8% water) sheets were tested. Increasing moisture content was reached by the soaking of "dry" PVB sheet in water for 14 days (Grachev, Klimenko, 1974).

Samples stressed by kneading were prepared in the Brabender kneader with two blunders W50 at the friction of 2:3. Volume of the heated chamber was of 55 cm3. Constant amount of

These corresponded to the top m/e ratio for acetic acid, butenal, butyraldehyde, benzene and toluene the expected products from the thermal decomposition of PVB (Wade, D'Errico,

Little or no degradation products were observed below 250 °C although the PVB samples had lost about 10–12% of mass under these experimental conditions were initially. The major products of the decomposition were observed above 260 °C. Acetic acid was a minor component of the volatile degradation products. Aromatic species, such as benzene and toluene, were also observed. These have been attributed to the break down of the polyene

From the relative % mass loss and the absence of volatiles detected by the mass spectrometer it was deduced that the PVB was primarily losing plasticizer in the temperature volatilization process between 200 and 260 °C. The loss of additives from a polymer is a complex process involving diffusion, transport and evaporation from the

By the reason of finding degradation mechanism of plasticized PVB, this material was reprocessed by kneading, rolling and pressing. Both dry (0.5 % water) and wet (8% water) sheets were tested. Increasing moisture content was reached by the soaking of "dry" PVB

Samples stressed by kneading were prepared in the Brabender kneader with two blunders W50 at the friction of 2:3. Volume of the heated chamber was of 55 cm3. Constant amount of

Fig. 2. TGA evaluation of plasticized Butacite PVB sheet.

products produced by the elimination reactions.

sheet in water for 14 days (Grachev, Klimenko, 1974).

surface of the polymer.

**6.1 Samples preparation** 

**6. Degradation by kneading** 

2004).

40 g PVB was placed in the chamber and processed for 10 minutes at different temperatures (100, 130, 160, 190, 220 °C) and rotation speeds (40, 60, 80 rpm). The chamber of kneader was filled only to the ¾ of the volume in order to have the sufficient amount of oxygen in order to study thermo-oxidative degradation. During kneading, both thermo-oxidative and shear degradation are assumed to take place.

In order to simulate solely shear degradation with absence of thermal stress, PVB sheets were re-processed by rolling at the temperature of 78°C in the presence of air. Laboratory double-roller was used. Rollers were preheated to 60-70°C in order to allow the PVB calendaring corresponding to processing of the rubber. After the initial preheating, the roller temperature was kept only by the energy dissipation. After 10 minutes the temperature reached 78°C and this value remained almost unchanged.

Pure thermal degradation with low shear stress was simulated by pressing. PVB was placed between two PET sheets preventing the contact with air and thus oxidative degradation. Then, the material was pressed at 1 MPa at temperature of 160, 190 a 220°C for 10 minutes.

Dry PVB was tested at all the above presented conditions; wet one was tested at all temperatures but only with 60 rpm.

### **6.2 Analysis and methods**

Mechanical properties of the stressed samples were determined using a T 2000 Tensile tester *(Alpha Technologies)* with the displacement rate of 500 mm/min at room temperature. For testing, material was pressed onto the plates with the thickness of 1.0 mm at the temperature of 130°C and the standard testing specimens were prepared. Tensile strengths and strain were determined.

Rheological properties of re-processed samples were tested in terms of MFI measurements using the extruding plastometer M201 (Haake) according to EN ISO 1133. Samples were conditioned at 25% relative humidity and then extruded at 150 °C through the 2 mm capillary using the load of 100 N. The MFI correlates to the polymer mass passing through a standard capillary in an interval of 10 minutes, at a given load.

Quantification of water content was carried out by the Karl Fischer method *(Metrohm AG)*. The method is based on the conductometric determination of water evaporated from the sheet into the iodine solution and sulphur dioxide in methanol.

Yellowness was evaluated using the CIE Lab. colour scale. Handy Color *(BYK Gardner)* instrument was applied and calibrated with the white and black standards. Measurement was carried out against the white background at the angle of 10°. Illumination type of D65 corresponding to daylight was applied. Yellowness YID, was calculated from the measurements of spectroscopic values L, a and b. The obtained value was converted to the value corresponding to the PVB sheet with the standard thickness of 0.76 mm, which is typical for applications in automotive industry and in architecture.

Thermo-gravimetric analysis (TGA) was determined by thermogravimetric analyzer TGA Q500 *(TA Instruments, New Castle, USA)* in open platinum crucibles and weighed-in. Amount of PVB sample for thermal analysis was approx. 8 mg and measurements were

PVB Sheet Recycling and Degradation 141

It is consequence of thermo-oxidative degradation, which causes reduction of polymer molecular weight. However, at the rotation speed of 80 rpm, the MFI values behave differently. Degradation of PVB macromolecular chains (expressed as increasing of MFI) is reduced at the temperatures above 190 °C, which is indicated by no rising or even slight drop of MFI (see Fig.3). The lowering of the degradation at the higher rotation speed (above 80 rpm) is possible to explain by the sliding of polymer chains in the stressed melt resulting

The results obtained from the measurement of tensile strength of the "dry" PVB samples (0.5 % moisture content) in dependence on speed of the kneading shaft are shown in Figure 4. At lower temperatures, degradation of "dry" PVB is proportional to increase of the rotation speed. For example, during processing at 100 °C degradation increased, which can be concluded from the lowering of stress at break values (shape of the curve in concave). On the other hand, increasing of temperature caused straightening of this dependence and for the samples processed above 160 °C the curves exhibit the convex curving. Minima on the curves observed at rotation speed of 60 rpm and temperatures 190 and 220 °C indicate, hence, the highest degradation of PVB. Samples re-processed by pressing were used as a background for the kneaded samples at the same temperatures. Slight increase of tensile strength, strain at break, MFI and yellowness were observed for the samples pressed for 10

Fig. 4. Tensile strength of the re-processed PVB sheet at the different conditions of the

During the PVB re-processing on the Brabender kneader the temperature of the kneading chamber was measured. The chamber was tempered on the required temperature, but with on-going process of kneading, the temperature slightly increased. The course of temperature

in the lower effect of kneading.

minutes at the all tested temperatures.

kneading of PVB sheet with water content 0.5%.

**6.4 The transformation of the process energy into heat** 

taken in temperature interval 20-500 °C, dT/dt = 10 °C min-1 in protective nitrogen atmosphere (150 mL min-1).

GPC analyses were conducted using a PLGPC-50 (*Polymer Laboratories)* equipped with a PL differential refractometer (DRI) and on-line viscometer detectors (VIS). Analyses were performed with a PL gel Mixed-C column *(7.8 x 300 mm; Polymer Laboratories)* at 30 °C with the mobile phase flow rate of 1 mL/min. Tetrahydrofurane was used as the mobile phase. The column was calibrated using narrow molecular weight polystyrene standards *(Polymer Laboratories Ltd, Church Stretton, UK*) with molecular weights ranging from 580 to 451 000 g.mol-1 (given by supplier). A 100 μL injection loop was used for all measurements. For the determination of molecular weight, universal calibration was applied. Data processing was performed with Cirrus GPC, Multi Detector Software. The concentration was of about 0.2 g /100 ml and samples were dissolved at room temperature for 20 hours under stirring. The combination of both types of detectors enabled to exactly determine molecular weight as well as detect the PVB aggregation.

#### **6.3 The influence of kneading conditions on the change of plasticized PVB sheet properties**

From the theory and practice it is confirmed that the PVB re-processing brings about the shortening of macromolecular chains, which induces the change of its mechanical properties. The results show that increasing of the re-processing temperature brought the lowering of melt rigidity (measured as MFI), lowering of tensile strength and strain. These changes are visualized in Figs. 3-4.

The MFI values are shown in Fig.3. To sum up, the MFI increases with the increasing of reprocessing temperature and the increasing of rotation speed systematically up to 60 rpm.

Fig. 3. The change of MFI at the different conditions of the kneading of PVB sheet with water content 0.5%.

taken in temperature interval 20-500 °C, dT/dt = 10 °C min-1 in protective nitrogen

GPC analyses were conducted using a PLGPC-50 (*Polymer Laboratories)* equipped with a PL differential refractometer (DRI) and on-line viscometer detectors (VIS). Analyses were performed with a PL gel Mixed-C column *(7.8 x 300 mm; Polymer Laboratories)* at 30 °C with the mobile phase flow rate of 1 mL/min. Tetrahydrofurane was used as the mobile phase. The column was calibrated using narrow molecular weight polystyrene standards *(Polymer Laboratories Ltd, Church Stretton, UK*) with molecular weights ranging from 580 to 451 000 g.mol-1 (given by supplier). A 100 μL injection loop was used for all measurements. For the determination of molecular weight, universal calibration was applied. Data processing was performed with Cirrus GPC, Multi Detector Software. The concentration was of about 0.2 g /100 ml and samples were dissolved at room temperature for 20 hours under stirring. The combination of both types of detectors enabled to exactly determine molecular weight as

**6.3 The influence of kneading conditions on the change of plasticized PVB sheet** 

From the theory and practice it is confirmed that the PVB re-processing brings about the shortening of macromolecular chains, which induces the change of its mechanical properties. The results show that increasing of the re-processing temperature brought the lowering of melt rigidity (measured as MFI), lowering of tensile strength and strain. These

The MFI values are shown in Fig.3. To sum up, the MFI increases with the increasing of reprocessing temperature and the increasing of rotation speed systematically up to 60 rpm.

Fig. 3. The change of MFI at the different conditions of the kneading of PVB sheet with

atmosphere (150 mL min-1).

well as detect the PVB aggregation.

changes are visualized in Figs. 3-4.

**properties** 

water content 0.5%.

It is consequence of thermo-oxidative degradation, which causes reduction of polymer molecular weight. However, at the rotation speed of 80 rpm, the MFI values behave differently. Degradation of PVB macromolecular chains (expressed as increasing of MFI) is reduced at the temperatures above 190 °C, which is indicated by no rising or even slight drop of MFI (see Fig.3). The lowering of the degradation at the higher rotation speed (above 80 rpm) is possible to explain by the sliding of polymer chains in the stressed melt resulting in the lower effect of kneading.

The results obtained from the measurement of tensile strength of the "dry" PVB samples (0.5 % moisture content) in dependence on speed of the kneading shaft are shown in Figure 4. At lower temperatures, degradation of "dry" PVB is proportional to increase of the rotation speed. For example, during processing at 100 °C degradation increased, which can be concluded from the lowering of stress at break values (shape of the curve in concave). On the other hand, increasing of temperature caused straightening of this dependence and for the samples processed above 160 °C the curves exhibit the convex curving. Minima on the curves observed at rotation speed of 60 rpm and temperatures 190 and 220 °C indicate, hence, the highest degradation of PVB. Samples re-processed by pressing were used as a background for the kneaded samples at the same temperatures. Slight increase of tensile strength, strain at break, MFI and yellowness were observed for the samples pressed for 10 minutes at the all tested temperatures.

Fig. 4. Tensile strength of the re-processed PVB sheet at the different conditions of the kneading of PVB sheet with water content 0.5%.

#### **6.4 The transformation of the process energy into heat**

During the PVB re-processing on the Brabender kneader the temperature of the kneading chamber was measured. The chamber was tempered on the required temperature, but with on-going process of kneading, the temperature slightly increased. The course of temperature

PVB Sheet Recycling and Degradation 143

Fig. 6. The influence of water content on the change of mechanical properties of no

During the re-processing of wet PVB material at the higher temperature, hydrolysis and elimination of butyric group can occur. This process results in the formation of hydroxyl groups and consequently conjugated double bond, which brings the change of PVB chain structure (Wade, D'Errico, 2004; Remsen, 1991). Thus, the hydrolysis causes considerable changes of the final properties of re-processed PVB. Due to this fact, an effort was done to find the optimal conditions for PVB re-processing with as low hydrolysis as possible. Hydrolysis was qualitatively estimated from the changes of molecular weight and

Although water present in PVB evaporates very quickly at the beginning of the process, it influences the results of all the tests. The values of MFI for re-processed "wet" PVB show the significant increase in the dependence on temperature in the comparison with the "dry" PVB (see Fig. 7). A notable increasing of MFI values observed for wet PVB is caused by the degradation, which is induced by thermo oxidative reactions and better diffusion of gases

The comparison of mechanical properties of "dry" and "wet" PVB presents Fig. 8. The figure shows tensile strength and strain of both PVB types kneaded at different temperatures at the constant rotation speed of 60 rpm. Arrows denote the values measured for the original "dry" PVB. Optimal processing temperature for "dry" PVB, where the degradation was the lowest, is determined at 150 °C as the maximum of the curve. This maximum, with the highest values of tensile strength, corresponds to the minimum degradation of PVB. Below and above 150 °C tensile strength decrease; this can be caused by the lowering of the molecular weight induced by the degradation. Regarding the degradation mechanism, the scission of the "dry" PVB chains less than 150 °C is prevailingly caused by shear stress, whilst at higher temperatures thermo-oxidative degradation takes

re-processed PVB sheet.

into the PVB melt.

place.

increasing of the sheet yellowness.

changes is summarized in Figure 5. The more noticeable energy transformation was observed at the lower processing temperatures (100 and 130 °C). This effect is clearly correlated to the higher rigidity of the processed material. It is also demonstrated that the evolution of dissipation heat depends on the rotation speed and kneading time. With the higher rotation speed, the amount of dissipated heat rises significantly. Above 130 °C the heat was formed only at the beginning of the kneading, when the material was still rigid enough. At 220 °C, due to the low material rigidity, the evolution of the transformation heat is minimal.

Fig. 5. Temperature change during the kneading process at different temperatures.

#### **7. The influence of water on the change of mechanical properties**

In order to lower the energy consumption during the PVB re-processing, its hygroscopicity was employed. As water presented in the PVB matrix can act as an additional plasticizer, it can decrease PVB rigidity (Tupý, Měřínská, 2010). It is supposed that lower material rigidity can decrease the energetic intensity of the re-processing. The comparison of MFI values measured for dry (0.5 % water) a wet samples (8 % water) shows that MFI increases proportionally to the water content (see Fig. 6). On the contrary, the tensile strength decreased. The change of the mechanical properties of "wet" PVB was caused by higher polymer plasticity and the reduction of intermolecular forces.

changes is summarized in Figure 5. The more noticeable energy transformation was observed at the lower processing temperatures (100 and 130 °C). This effect is clearly correlated to the higher rigidity of the processed material. It is also demonstrated that the evolution of dissipation heat depends on the rotation speed and kneading time. With the higher rotation speed, the amount of dissipated heat rises significantly. Above 130 °C the heat was formed only at the beginning of the kneading, when the material was still rigid enough. At 220 °C, due to the low material rigidity, the evolution of the transformation heat

Fig. 5. Temperature change during the kneading process at different temperatures.

In order to lower the energy consumption during the PVB re-processing, its hygroscopicity was employed. As water presented in the PVB matrix can act as an additional plasticizer, it can decrease PVB rigidity (Tupý, Měřínská, 2010). It is supposed that lower material rigidity can decrease the energetic intensity of the re-processing. The comparison of MFI values measured for dry (0.5 % water) a wet samples (8 % water) shows that MFI increases proportionally to the water content (see Fig. 6). On the contrary, the tensile strength decreased. The change of the mechanical properties of "wet" PVB was caused by higher

**7. The influence of water on the change of mechanical properties** 

polymer plasticity and the reduction of intermolecular forces.

is minimal.

Fig. 6. The influence of water content on the change of mechanical properties of no re-processed PVB sheet.

During the re-processing of wet PVB material at the higher temperature, hydrolysis and elimination of butyric group can occur. This process results in the formation of hydroxyl groups and consequently conjugated double bond, which brings the change of PVB chain structure (Wade, D'Errico, 2004; Remsen, 1991). Thus, the hydrolysis causes considerable changes of the final properties of re-processed PVB. Due to this fact, an effort was done to find the optimal conditions for PVB re-processing with as low hydrolysis as possible. Hydrolysis was qualitatively estimated from the changes of molecular weight and increasing of the sheet yellowness.

Although water present in PVB evaporates very quickly at the beginning of the process, it influences the results of all the tests. The values of MFI for re-processed "wet" PVB show the significant increase in the dependence on temperature in the comparison with the "dry" PVB (see Fig. 7). A notable increasing of MFI values observed for wet PVB is caused by the degradation, which is induced by thermo oxidative reactions and better diffusion of gases into the PVB melt.

The comparison of mechanical properties of "dry" and "wet" PVB presents Fig. 8. The figure shows tensile strength and strain of both PVB types kneaded at different temperatures at the constant rotation speed of 60 rpm. Arrows denote the values measured for the original "dry" PVB. Optimal processing temperature for "dry" PVB, where the degradation was the lowest, is determined at 150 °C as the maximum of the curve. This maximum, with the highest values of tensile strength, corresponds to the minimum degradation of PVB. Below and above 150 °C tensile strength decrease; this can be caused by the lowering of the molecular weight induced by the degradation. Regarding the degradation mechanism, the scission of the "dry" PVB chains less than 150 °C is prevailingly caused by shear stress, whilst at higher temperatures thermo-oxidative degradation takes place.

PVB Sheet Recycling and Degradation 145

The comparison of "dry" and "wet" PVB indicates that water acts as a plasticizer and "wet" material is less stressed during re-processing and. Hence, the more plasticized "wet" PVB is not significantly stressed by shear and is mostly degraded by thermo oxidative degradation.

The PVB degradation was the most markedly reflected through the changes of PVB yellowness. Visually and also instrumentally, the yellowness (sometimes even brownness) of re–processed PVB samples was noticeable. Yellowness increased significantly with increasing of re-processing temperature. In the case of "dry" PVB, significant color change was observed above 130 °C. Color of "wet" PVB was significantly changed above 160 °C (Fig. 9). Measurements demonstrated that during kneading at the temperatures below 160 °C yellowness was almost unchanged. This can be explained by the stabilizing function of higher moisture content and consequently higher grade of PVB plasticization. At temperatures lower than 130 °C, the change of the yellowness is insignificantly irrespective of water content. With the increasing temperature, the yellowness grew markedly. This can be explained by thermo oxidative reactions between oxygen and PVB accompanied by better gas diffusion as well as by water induced hydrolysis. It was reported that during hydrolysis, conjugated double bonds are formed [35]. These are more reactive and bring more intensive lowering of molecular weight. The results from the yellowness

measurements corresponds the results from determination of MFI (see Fig. 7).

Fig. 9. Yellowness of kneaded PVB samples with different water content (0.5 % and 8 %) at

60 rpm during ten minutes.

**7.1 The influence of water on the yellowness** 

Fig. 7. MFI of kneaded PVB samples with different water content (0.5 % and 8 %) at 60 rpm during ten minutes.

Fig. 8. Tensile strength of kneaded PVB samples with different water content (0.5 % and 8 %) at 60 rpm; arrows point out to values of virgin PVB sheet.

For the wet PVB, the values of stress at break and strain are systematically higher compared to those measured for dry samples. Moreover, dependence stress and strain *vs* temperature is monotonously decreasing not showing maxima or minima. The increase can be explained by the intramolecular crosslinking formed by the hydrogen bonds.

Fig. 7. MFI of kneaded PVB samples with different water content (0.5 % and 8 %) at 60 rpm

Fig. 8. Tensile strength of kneaded PVB samples with different water content (0.5 % and 8 %)

For the wet PVB, the values of stress at break and strain are systematically higher compared to those measured for dry samples. Moreover, dependence stress and strain *vs* temperature is monotonously decreasing not showing maxima or minima. The increase can be explained

at 60 rpm; arrows point out to values of virgin PVB sheet.

by the intramolecular crosslinking formed by the hydrogen bonds.

during ten minutes.

The comparison of "dry" and "wet" PVB indicates that water acts as a plasticizer and "wet" material is less stressed during re-processing and. Hence, the more plasticized "wet" PVB is not significantly stressed by shear and is mostly degraded by thermo oxidative degradation.

#### **7.1 The influence of water on the yellowness**

The PVB degradation was the most markedly reflected through the changes of PVB yellowness. Visually and also instrumentally, the yellowness (sometimes even brownness) of re–processed PVB samples was noticeable. Yellowness increased significantly with increasing of re-processing temperature. In the case of "dry" PVB, significant color change was observed above 130 °C. Color of "wet" PVB was significantly changed above 160 °C (Fig. 9). Measurements demonstrated that during kneading at the temperatures below 160 °C yellowness was almost unchanged. This can be explained by the stabilizing function of higher moisture content and consequently higher grade of PVB plasticization. At temperatures lower than 130 °C, the change of the yellowness is insignificantly irrespective of water content. With the increasing temperature, the yellowness grew markedly. This can be explained by thermo oxidative reactions between oxygen and PVB accompanied by better gas diffusion as well as by water induced hydrolysis. It was reported that during hydrolysis, conjugated double bonds are formed [35]. These are more reactive and bring more intensive lowering of molecular weight. The results from the yellowness measurements corresponds the results from determination of MFI (see Fig. 7).

Fig. 9. Yellowness of kneaded PVB samples with different water content (0.5 % and 8 %) at 60 rpm during ten minutes.

PVB Sheet Recycling and Degradation 147

resulting in chain scission caused by mechanical stress, Temperature region between 150 °C and 180 °C seems to be favorable for reprocessing of dry PVB. Here, only minor changes in the sample are observed and molecular weights stay almost unchanged. For wet PVB, which posses at lower temperatures low stiffness, molecular weight tends to decrease with increasing processing temperature. At temperatures above 190 °C, molecular weight of dry PVB is comparable to that measured for wet sample. Hence, it can be assumed that degradation mechanism in this temperature region is similar. From Fig.11 it is also obvious that molecular weights of the wet PVB samples, with the exception of the sample processed at 220 °C, were systematically higher compared to dry

Fig. 11. Influence of kneading temperature on changes of weight average of molecular weight (Mw) recorded for (0.5% of water) dry and wet (8.0 % of water) PVB sheet.

In the presented work, conditions for re-processing of plasticized PVB sheets were investigated and influence of temperature, air oxygen content and mechanical stress on the course of degradation was studied. In order to find the possibility for reduction of energy consumption during re-processing, effect of moisture content in PVB sheets on processing

ones.

**9. Conclusions** 

#### **8. The change of solution properties influenced by the degradation**

Changes in molecular weight and molecular weight distribution of virgin and processed material were followed by gel permeation chromatography. Differential distribution curves of virgin and processed samples (kneading, 100°C, dry) are compared in Fig. 10. From figure it is obvious that the entire distribution of the processed sample compared to virgin one is shifted to lower molecular weight region, which indicates degradation. Moreover the processed sample contains small but distinct peak with molecular weights higher that 2x106 g.mol-1 (labeled with arrow). This peak was observed for all the processed samples irrespective temperature and type of processing and its presence indicates that diluted solutions of processed samples contain structures with high molecular weight – aggregates. The aggregation of PVB solution and difficulties with polymer dissolution, even in thermodynamically good solvents, has been reported by several authors (Měřínská, Tupý, 2009; Remsen, 1991).

Fig. 10. Comparison of molecular weight distribution curves of virgin and processed PVB (100 °C, dry).

Changes of molecular weight in terms of Mw as a function of increased kneading temperature are for wet and dry samples depicted in Fig. 11. For dry sample, the lowest Mw values (weight average of molecular weight) were measured on samples processed below 150 °C. Under these conditions, predominantly shear degradation takes place

Changes in molecular weight and molecular weight distribution of virgin and processed material were followed by gel permeation chromatography. Differential distribution curves of virgin and processed samples (kneading, 100°C, dry) are compared in Fig. 10. From figure it is obvious that the entire distribution of the processed sample compared to virgin one is shifted to lower molecular weight region, which indicates degradation. Moreover the processed sample contains small but distinct peak with molecular weights higher that 2x106 g.mol-1 (labeled with arrow). This peak was observed for all the processed samples irrespective temperature and type of processing and its presence indicates that diluted solutions of processed samples contain structures with high molecular weight – aggregates. The aggregation of PVB solution and difficulties with polymer dissolution, even in thermodynamically good solvents, has been reported by several authors (Měřínská, Tupý,

**virgin PVB** 

**processed PVB** 

**Molecular weight (MW)** 

Fig. 10. Comparison of molecular weight distribution curves of virgin and processed PVB

Changes of molecular weight in terms of Mw as a function of increased kneading temperature are for wet and dry samples depicted in Fig. 11. For dry sample, the lowest Mw values (weight average of molecular weight) were measured on samples processed below 150 °C. Under these conditions, predominantly shear degradation takes place

**8. The change of solution properties influenced by the degradation** 

2009; Remsen, 1991).

(100 °C, dry).

**dW / dlog M** 

resulting in chain scission caused by mechanical stress, Temperature region between 150 °C and 180 °C seems to be favorable for reprocessing of dry PVB. Here, only minor changes in the sample are observed and molecular weights stay almost unchanged. For wet PVB, which posses at lower temperatures low stiffness, molecular weight tends to decrease with increasing processing temperature. At temperatures above 190 °C, molecular weight of dry PVB is comparable to that measured for wet sample. Hence, it can be assumed that degradation mechanism in this temperature region is similar. From Fig.11 it is also obvious that molecular weights of the wet PVB samples, with the exception of the sample processed at 220 °C, were systematically higher compared to dry ones.

Fig. 11. Influence of kneading temperature on changes of weight average of molecular weight (Mw) recorded for (0.5% of water) dry and wet (8.0 % of water) PVB sheet.

#### **9. Conclusions**

In the presented work, conditions for re-processing of plasticized PVB sheets were investigated and influence of temperature, air oxygen content and mechanical stress on the course of degradation was studied. In order to find the possibility for reduction of energy consumption during re-processing, effect of moisture content in PVB sheets on processing

PVB Sheet Recycling and Degradation 149

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parameters and degradation was examined. The obtained results show that, based on the evaluation of MFI and mechanical properties, the optimal conditions for PVB re-processing by kneading occur at the temperature of about 150°C and rotation speed of kneader lower than 60 rpm. These conclusions are in the good agreement with the measurement of PVB yellowness. Below 150 °C yellowness remained almost unchanged and increased significantly above this temperature. GPC measurements corroborate the above conclusions showing minimal changes of PVB molecular weigh for this temperature. Increased amount of water in PVB sheet can act as and additional plasticizer improving workability of polymer melt and decreasing this energy consumption. However the "wet" samples are more susceptible to hydrolytic degradation and compromise decision has to be taken to find the balance between these two effects.

#### **10. Acknowledgement**

This article was written with support of Operational Program Research and Development for Innovations co-funded by the European Regional Development Fund (ERDF) and national budget of Czech Republic, within the framework of project Centre of Polymer Systems (reg. number: CZ.1.05/2.1.00/03.0111).

#### **11. References**


parameters and degradation was examined. The obtained results show that, based on the evaluation of MFI and mechanical properties, the optimal conditions for PVB re-processing by kneading occur at the temperature of about 150°C and rotation speed of kneader lower than 60 rpm. These conclusions are in the good agreement with the measurement of PVB yellowness. Below 150 °C yellowness remained almost unchanged and increased significantly above this temperature. GPC measurements corroborate the above conclusions showing minimal changes of PVB molecular weigh for this temperature. Increased amount of water in PVB sheet can act as and additional plasticizer improving workability of polymer melt and decreasing this energy consumption. However the "wet" samples are more susceptible to hydrolytic degradation and compromise decision has to be taken to find

This article was written with support of Operational Program Research and Development for Innovations co-funded by the European Regional Development Fund (ERDF) and national budget of Czech Republic, within the framework of project Centre of Polymer

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the balance between these two effects.

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**10. Acknowledgement** 

**11. References** 


http://www.sekisui.co.jp/cs/eng/products/type/slecbk/tech/1183758\_5127.html


**6** 

*Mexico* 

**Materials and Methods for the Chemical** 

*Applied Chemistry Research Group, Departamento de Ciencias Básicas, Universidad Autónoma Metropolitana, Azcapotzalco, México D. F.* 

Nowadays, plastics play a fundamental role in modern life, they are included in all productive chains. Plastics frequently replace more traditional materials such as wood, metal, glass, leather, paper and rubber because they can be lighter, stronger, corrosion resistant, acid and base resistant, durable and a better insulators. Plastics are polymers with high molecular weight and usually synthesized from low molecular weight compounds, although they can be obtained also through the chemical modification of high molecular

Plastics can be divided into two major groups, according to their thermal behavior: thermosets and thermoplastics. Thermoplastics soften when they are exposed to heat, and they can be molded and shaped, this heating process can be repeated many times. These plastics contribute to the total plastic consumption by roughly 80% and are used as containers, packaging, trash bags and other non-durable goods (Al-Salem et al., 2009). Some examples are high and low density polyethylene (HDPE, LDP), polystyrene (PS), polypropylene (PP) and polyvinyl chloride (PVC). In contrast, thermosets solidify irreversibly when heated, since an irreversible network of cross-linked covalent bonds is formed, giving a hard, durable, strength and heat resistant products. Such is the case of unsaturated polyurethane (PU), unsaturated polyesters and, alkyd, phenolic and epoxy resins. For that reason, they are used primarily in automobiles, construction adhesives, furniture, kitchenware, inks, and coatings. A third group of plastics, rubber-type, are named elastomers, formed by slightly cross-linked polymer chains; in less proportion than thermosets, giving to these materials elastic properties and relatively good resistance

In the last thirty years, plastic industry has raised very quickly, growing around 500%. In 2008, the global plastic production was 245 Mt; the European Community accounts for around 25% of world production, whereas the United States by around 13%; China alone accounts for 15%. Polyethylene has the highest share of production of any polymer type and the packaging and construction sectors represent more than 50% of plastic demand (EC,

(Morton-Jones, 1993; Aguado & Serrano, 2007, Scheirs & Kaminsky, 2006).

weight natural materials such as cellulose (Gervet, 2007).

**1. Introduction** 

2011; USEPA, 2008).

**Catalytic Cracking of Plastic Waste** 

Luis Noreña, Julia Aguilar, Violeta Mugica,

Mirella Gutiérrez and Miguel Torres

