Recovery of PET/PA66 Composites

At present, China's soft drink production has increased at an average annual growth rate of more than 20%, and its demand for polyethylene terephthalate (PET) bottles for packaging has also grown at an average annual rate of 18%. According to statistics, about 1.4 million tPET bottles were discarded in China in 2005, causing serious pollution problems. How to recycle a large number of waste PET bottles

Recycling has become a social problem that needs to be solved. The development of advanced recycling technology will significantly increase the proportion of "upgrade and utilization" of PET bottles, which will facilitate the comprehensive utilization of resources, reduce pollution, solve the worries of the development of the packaging industry, and open up new economic growth points. In order to recycle and reuse PET, people have done a lot of work [1–5], and relatively few studies have used recycled PET to make engineering plastics.

Because recycled PET (abbreviated as rPET) has the problems of low intrinsic viscosity, poor flow stability, difficulty in demolding, and poor impact properties, it cannot generally be directly processed by injection and extrusion molding processes. On the other hand, polyamide 66 (PA66) has excellent comprehensive properties and is widely used in industries such as automobiles and machinery, but it is expensive. However, the price of rPET is low, and the melting point of PA66 is very similar. Therefore, the research and development of rPET/PA66 composite materials will not only solve the problem of PET recycling, but also reduce the cost of PA66 and bring about better economic benefits.

First, the experimental part

(a) raw materials

rPET: bottle-level, the United States URRC company;

PA66: LEONA 5KR58M, Asahikasei Chemical Company; compatilizer OZ: oxazoline copolymer, homemade.

(B) Equipment and Instruments

High-speed mixer: SHR-5, Zhangjiagang Ruida Machinery Manufacturing Factory;

Twin Screw Extruder: TSE-35, Nanjing Ruiya Polymer Equipment Co., Ltd.;

Injection molding machine: HTB II0X/1, Ningbo Haitian Machinery Co., Ltd.;

Electronic universal testing machine: Model 4465, American Instron Corporation; Impact testing machine: Uinversal type, British Ray-ran company;

Scanning Electron Microscopy (SEM): Model S-2150, Hitachi High-Technologies Corporation, Japan;

Thermal deformation Vicat temperature measuring instrument: WKW-300 type, Changchun Intelligent Instrument Equipment Co., Ltd.;

Rotary Rheometer: Gemini 200HR, Bohlin In2struments, UK.

(three) sample preparation

First, a certain amount of dried rPET, PA66 and compatibilizer are mixed in a high-speed mixer, and then the mixed material is added to a twin-screw extruder to react and extrude at a set temperature and a screw speed for water cooling. The pellets were made into rPET/PA66 composite pellets. The pellets were dried in an oven at 120° C. for 8 h, and then the injection molding machine was used to injection-mold standard specimens.



(four) performance testing

Tensile properties were tested according to ASTM D638-03.

Impact performance is tested according to ASTM D256-04.

Morphology observation: The extruded spline was fractured under liquid nitrogen, observed by SEM after vacuum gold plating and photographed, and the accelerating voltage was 15 kV. Dynamic rheological properties: The test temperature was 270°C, the frequency was set to 0.01 - 10 Hz, and the strain was set to 0.01 (in the linear viscoelastic region). Static shear viscosity: the test temperature was 270°C, and the shear rate was 0.01 to 10 s -1.

Vicat softening temperature: The sample size was 10 mm × 10 mm, the load was 10 N, and the heating rate was 5°C/6 min (initial temperature 40°C, constant temperature 300 s).

Second, the results and discussion

(I) Effect of PA66 dosage on mechanical properties of rPET/PA66 composites

Because the viscosity of rPET and PA66 is very low, and the compatibility between them is poor, the material flows into liquid droplets during extrusion and it is difficult to form strips. Therefore, the compatibility agent OZ is added to modify it. After the addition of the compatibilizer, the viscosity of the material rises significantly and can be extruded using an extruder to granulate.

Effect of PA66 Content on Mechanical Properties of rPET/PA66 Composites . With the increase of the amount of PA66, the tensile strength of the material showed an upward trend, and the change of the notched Izod impact strength was more complicated than the situation. When the mass fraction of PA66 is 60%, the material has the highest notched impact strength and high tensile strength. Taken together, the PA66 mass fraction was chosen to be 60%.

(II) Effect of the amount of compatibilizer on the mechanical properties of rPET/PA66 composites

The mass fraction of fixed PA66 was 60%. The effect of the amount of compatibilizer OZ on the mechanical properties of rPET/PA66 composites was investigated.

With the increase of the amount of compatibilizer, the tensile strength and impact strength of the material increase first and then decrease slightly. This is because when the amount of compatibilizer is too small, the compatibilization of the material system is not obvious enough, and if the compatibilizer is used in too much amount, the reaction is violent and the viscosity of the system is rapidly increased, resulting in processing difficulties, and at the same time, the system contains Many lower molecular weight compatibilizers have degraded performance. The mass fraction of the compatibilizer used was 5%, and the mechanical properties of the material were superior at this time.

(III) Morphological Structure of rPET/PA66 Composites

To further understand the effect of the compatibilizer, the author examined the morphological structure of the rPET/PA66 composite material. The system without the compatibilizer showed obvious phase separation, and the disperse phase had a large size; along with the amount of compatibilizer With the increase, the phase interface has become blurred, and the size of the dispersed phase gradually decreases until it disappears. Due to the oxazoline group in the molecular structure of the compatibilizer OZ, it can react with both the carboxyl group of the PET terminal and the amine group of the PA66 terminal, which may generate the block copolymer of PET and PA66 in situ. Thus, the compatibility of the rPET/PA66 material is significantly improved.


(d) Rheological properties of rPET/PA66 composites

A group of rPET/PA66 composites with good mechanical properties were selected and their rheological behaviors were studied. The static rheological curves PA66 and rPET/PA66 composites of pure PA66 and composites exhibit pseudoplastic fluid behavior, ie, the melt viscosity decreases with increasing shear rate. This is because during the flow of the polymer, the shear rate or shear stress increases the molecular chain unwrapping and the molecules are oriented, which reduces the viscosity [6]. At the same shear rate, the shear viscosity of composites was significantly higher than that of PA66, which further confirmed that the compatibilizer OZ chemically reacted with PA66 and PET to increase the molecular weight of the system and increase the melt viscosity.

Dynamic rheological curves of pure PA66 and rPET/PA66 composites, where the storage modulus G′ represents the elastic component of the fluid and the loss modulus G′′ represents the viscous component of the fluid. The G′ curve of PA66 is in the rPET/PA66 complex. Below the G′ curve of the material, this shows that the stiffness of the PA66 melt is lower than that of the rPET/PA66 composite melt, which also proves that the mechanical properties of the rPET/PA66 composite are indeed better than those of the pure PA66.rPET/PA66 composite The G′′ of the material is higher than that of pure PA66 at any frequency band, which indicates that the melt viscosity of rPET/PA66 composite is higher than that of PA66, which may be due to the compatibilizer reacting with PET and PA66 to form a larger molecular weight The block copolymer increases the viscosity.

(v) Thermal properties of rPET/PA66 composites

The thermal properties of rPET, pure PA66, and rPET/PA66 composites were investigated. The Vicat softening temperature of rPET was low. This may be due to the fact that PET used in the experiment was a recycled material. Although selected, all aspects of its performance are not The reduction was avoided. The Vicat softening temperature of rPET/PA66 composites is almost similar to that of pure PA66.

Third, the conclusion

(1) The reactive compatibilizer OZ can increase the melt viscosity of the rPET/PA66 composite, making the composite material easier to be extruded.

(2) With the increase of the amount of compatibilizer, the tensile strength and impact strength of the composite material increase first and then decrease slightly, and the microscopic morphology also transitions from the obvious phase interface to almost no phase interface.

(3) When the mass fraction of PA66 is 60% and the compatilizer OZ mass fraction is 5%, the mechanical and thermal properties of the rPET/PA66 composite are comparable to that of pure PA66.

Reprinted from: Plastics Industry Network