Venture Chemical Ltd. 652, Fukano, Muro, Uda City, NARA 632-0203 JAPAN

Telephone : +81-745-97-2111 Facsimile : +81-745-97-2112 http://www.venture-chemical.co.jp

Table 1. Collection of used PET bottles Municipalities Collection Sep. 2005 Japan PET Bottle Association 　　 Volume of collected bottles(ton) Production (ton) Rate of collection (%) 1995 2,594 142,110 1.8 1996 5,094 172,902 2.9 1997 21,361 218,806 9.8 1998 47,620 281,927 16.9 1999 75,811 332,202 22.8 2000 124,873 361,944 34.5 2001 161,651 402,727 40.1 2002 188,194 412,565 45.6 2003 211,753 436,556 48.5 2004 238,469 513,712 46.4 Total Collection 　　 Volume of collected bottles(ton) Production (ton) Rate of collection (%) 2001 177,186 402,727 44 2002 220,256 412,565 53.4 2003 226,405 436,556 61 2004 319,893 513,712 62.3 Remarks : Production is weight of Recycling designated PET bottles　(soft drinks, soy sauce and liquors)

Recycling PET was mainly reused as fibers and sheets as shown in the table 2. It is because such characteristics of recycling PET limited applicable molding method as the molecular weight reduction in molding where the melt viscosity might be decreased, and an extreme decrease in the impact strength without drawing. Fibers and sheets made by recycling PET, however, saturated the market already, so that the most of collected PET bottles began to be thrown out before recycling.

Under such circumstances, development of applicable method of injection and profile extrusion molding has been an essential issue for recycling PET.

Problem with recycling PET
In molding recycling PET, hydrolysis that may reduce the molecular weight is an unavoidable action when strictly controlling water. Hydrolysis of Recycling PET proceeds according to the following structure.

Such molecular weight reduction of recycling PET is the prime cause of a decrease in impact strength of a molded part without drawing process. And a decrease in the melt viscosity leads to running from nozzle and defective appearance in injection molding, and makes it difficult to be diluted for size enlargement in profile extrusion molding.

In order to solve these problems, we have developed and commercialized "AR-P-1100", recycling PET modifier, making use of the technology of styrene copolymer.


Recycling PET modifier AR-P-1100
AR-P-1100 may inhibit hydrolysis of recycling PET in molding to forcefully make it high molecules. Such main problems in using recycling PET as the decrease in impact strength and melt viscosity can be solved by adding a little amount of AR-P-1100. Recycling PET is modified by AR-P-1100 where elastic elements are uniformly dispersed in reactive parts so that they are polymerized. Interfacial adhesion between recycling PET and elastomer is reinforced, and impact strength is improved since elastic particles restrain crack spreading that likely to occur continuously and in laminae.

AR-P-1100 improves the melt viscosity of recycling PET, of which modification is entwinement between recycling PET and high-molecule-weight elastomers that are scattered in molecular chains being steric by graft polymerization in straight chains with reactive parts.

Additionally, AP-P-1100 is resistant to heat that can be blended with recycling PET and dried together without melting and softening.

General features and characteristics of AR-P-1100 are described as follows.

The table 4 shows the effect of AR-P-1100 to physical properties of recycling PET. Izod impact strength was markedly improved by adding a little amount of AR-P-1100. Besides, molded part preserved low-temperature impact strength inherent in PET and offered beautiful surface luster. Tensile yield strength, bending strength, and bend elastic modulus inclined to decrease. However, it can compete with general-purpose olefin in those values. Melt viscosity was also improved dramatically in the lower shear rates, that can prevent running from nozzle in injection molding, minimize inhaling of the air caused by suck back, consequently prevent such defective molding as flash, and stabilize measurement accuracy.

The improvement of melt viscosity by AR-P-1100 is also effective in extrusion molding. The graph 1 shows the correlation between shear rates and melt viscosity. By adding AR-P-1100 to recycling PET, the resin was viscous enough in lower shear rates to be applicable to profile extrusion molding, and became unsticky in higher shear rates mostly equivalent to pure recycling PET.

AR-P-1100 makes recycling PET possible to be used in various molding methods including injection and extrusion, producing such variation of melt viscosity depending on shear rates.

Graph 1. Correlation between shear rate and viscosity of recycling PET including AR-P-1100 Dice diameter : 1 mm Test temp. : 270℃ Pre-heating time : 300 sec. Graph 2. Spiral fluidity of recycling PET including AR-P-1100 　 Injection pressure : 100 Mpa Mold : 4 mm W x 3 mm T

Viscosity improvement of recycling PET, one of function of AR-P-1100, represents viscosity variation depending on shear rates. The resin with such varying viscosity may flow well in injection molding. The graph 2 shows spiral fluidity of recycling PET in case of adding AR-P-1100. The fluidity of recycling PET including 10 - 15% AR-P-1100 is nearly equivalent to that of recycling PET only when raising molding temperature by 10℃. This suggests that not only modified recycling PET is versatile in a wide range of molding conditions, but also it may retard heat degradation and hydrolysis of recycling PET by setting a lower molding temperature.

Graph 3. Weatherability of finished product containing 15% AR-P-1100

Precaution
(1)    AR-P-1100 requires no predrying
(2)    Recycling PET tends to be muddy in milky white by adding AR-P-1100.

Image 1. Viscosity improvement of recycling PET by adding AR-P-1100

As aforementioned, recycling PET is very weak in impact strength. Therefore, it is preferable to make a molded part with recycling PET before crystallizing. In order to keep recycling PET uncrystallized while molding, it is necessary to design a molded part with even radial thickness of 2 mm or less, and to keep die temperature as low as possible and rapidly cool it.

Besides, it is important in injection molding to raise injection speed as high as possible. Desirable mold structure is direct gate type with a high taper rate with which such demerits of recycling PET as a short gate seal time and a low shrinkage may be counterbalanced.

Because of characteristics described as (2) and (3), it is preferable that molding should be carried out at a temperature around 255℃ with a shorter residence time.

According to the above (4), it is necessary in injection molding to dry recycling PET preliminarily by a dryer. On the contrary, it is confirmed through actual equipment that by adding AR-P-1100, preliminary drying may not be needed in profile extrusion molding. Though it involves a few limitations including the need for a molding machine equipped with a vent (pressure reduction and suction devices are not needed), AR-P-1100 may satisfy such users' needs when newly introducing recycling PET as the reduction of the total running cost and unnecessity of introducing a new machine.

PET resin is versatile because of its inherent properties in luster, impact strength at low temperatures, chemical resistance, absence from toxicity, and wheatherability. It is desired that AR-P-1100 may contribute to the wide use of recycling PET.

Appendix

DESIRABLE MOLDING CONDITIONS IN USING OF RECYCLING PET WITH AR-P-1100

(1)    DESIRABLE CONDITIONS OF INJECTION MOLDING

Preparation

Predrying:

Drying Temp. at 130 〜 140℃, Time for 3 〜 5 hours
Any of dryer equipped with a dehumidifier (or an agitator) is preferable
In case of a chamber dryer, thickness of material on the pats (plate containers) of dryer should be 30 mm or so.

Molding conditions

Temperature:

Barrel temp. between 225 and 260℃; nozzle temp. 10℃ higher than barrel temp.
Feed zone should be set as low as possible.
e.g., C1 at 150℃; C2 at 200℃; C3 at 260℃; C4 at 260℃; N at 270℃
In raising the temperature at feed zone, it is possible to measure incorrectly since resin may become soft before screw, and adhere to the barrel.
Maximum molding temperature should be 280℃. In a high temperature exceeding such maximum temperature, resin may be physically degraded as yellowing or decomposing.

Plasticization and injection conditions:

Back-up pressure: set lower (between 2 and 10 kg/cm²)
Revolution: set faster (about 100 rpm) in order to minimize resin unevenness by residence time difference; it is preferable to postpone measurement in accordance with cooling time.
Suck back: minimize running from nozzle
Injection speed: set as fast as possible in order to minimize defects of finished product
Injection pressure: set higher in accordance with injection speed
Follow-up pressure: same pressure as general-purpose PET; pressure keeping time should be re-set for every mold according to gate diameter and shape; since PET may become a gate seal soon, it is hard to release molded parts from the mold if pressure keeping time is too long.
Screw type: general-purpose or full flight type screw is sufficient; a check ring (chuck ring) is needed.
Other notes: it is preferable to cool nozzle down to prevent cold slag, and to withdraw nozzle every batch to prevent die from heating.

Mold:

Mold temperature: below 40℃; it is preferable to use a chiller to cool die down so that impact strength of molded part may be improved
Cooling time: roughly same time as PVC

Other notes (for your information)

Preferable gate type is a direct gate with a taper of about 3 degrees. Ideally, the gate length should be shorter in order not to make a large gate diameter. Part strength near the gate may be poor or break-off may occur If the gate diameter is too large. Using a direct gate, it is possible to carry out molding smoothly.

L/t is limited by 250. In using general-purpose resin, L/t is extended by raising molding and die temperature. In using PET, however, such temperature control may result in vain. It is better to recondition hardware including gate replacement.

(2)    DESIRABLE CONDITIONS OF EXTRUSION MOLDING

Preparation

Predrying: basically it is unnecessary to predry. However, predrying at 140℃ may improve a little viscosity of resin and impact strength of molded part.

Molding conditions

Temperature:

Barrel temp. between 230 and 270℃; In a vent type machine, raise temperature before vent to accelerate exhaustion, so that physical properties of resin may be improved.
It is easy to size in a lower adapter and dies
e.g., C1 at 230℃; C2 at 250℃; C3 at 265℃; C4 at 260℃; AD at 250℃; D at 240℃
In starting up, adapter and dies temperature should be 260℃, and lower it gradually; If set as the above example from the beginning, it is possible to raise back-up pressure rapidly.
Maximum molding temperature should be 280℃. In a high temperature exceeding such maximum temperature, resin may be physically degraded as yellowing or decomposing.

Revolution: set revolution as fast as possible (about 100 rpm) in order to minimize degradation of physical properties of resin for a long residence time.

Machine specification:
A vent type machine equipped with a vent and 2 shafts is preferable. When using a machine with one shaft without vent, back-up pressure should be higher by inserting a mesh.
Screw: L/D = 25 to 30; a screw with high kneading disc is preferable, although a general-purpose screw design can be used.