Chemical recycling of waste polymer materials

Chemical cycle is one of the important methods of polymer material cycle, which refers to the degradation reaction of polymers under the action of heat and chemical reagents to form low-molecular weight products, which can be further utilized, such as monomer repolymerization, oil products can be further processed. At present, the main methods of chemical cycle are chemical degradation. Chemical degradation can be divided into depolymerization, pyrolysis, hydrogenation and gasification.

The present situation of chemical cycle development of polymer materials

1.       Step - by - step polymer material

The progressive polymer materials mainly include polyester and polyurethane, which are represented by polyethylene terephthalate. Mainly used for film, fiber and fabric, beverage bottle, etc. Waste materials can react with polyols in the presence of catalysts and the products can be condensed with unsaturated polyacids to make unsaturated polyresin. Different esters can be obtained by alcoholysis with different alcohols, either as monomers or as plasticizers. PET can be hydrolyzed under acidic or alkaline conditions. It can be hydrolyzed under normal pressure in strong acid (such as sulfuric acid and nitric acid) medium. The hydrolysis rate is fast. If it is hydrolyzed in an aqueous solution of alkaline (such as NaOH), 3-sh should be reacted at 21 2500C and 1.4-2.0mpa. After the reaction, TPAO weak alkali (such as hydrogen and oxygen) can be precipitated, and can also be used to hydrolyze PET waste to obtain monomer. Saponification reaction under atmospheric pressure has been applied in silver and TPAO polyurethane is from recycled PET film condensation polymer materials, can be hydrolyzed into the pluralistic alcohol and amine, with a special extruder hydrolysis, dibasic acid can be obtained by the purification of the product and diamine, diamine and reaction with phosgene, preparation of diisocyanate, used for foam production. But the cost of this process is large and the recovery benefit is not high. PU alcoholysis is a widely used method at present. PU waste materials can be alcoholyzed to obtain polyol mixture, which cannot be separated effectively at present, but this product can be used as a component in the manufacture of foam plastics and elastomers.

2.       Additive polymer material

Polystyrene (ps) in addition to used as paint, binder, but also used to crack styrene ps under the action of heat can be cracked into styrene, the yield of 65%, above. Japanese scientists have cracked PS in solvent method, decomposed it at 400 to 500 ℃ for 1 20min, and the condensate obtained can be distilled into styrene with a purity of 96%.High purity styrene can be obtained by fractionation using metal oxide as catalyst in melting state (>350 ℃).In addition, lead alloy is used as heating medium to crack ps. Under the action of appropriate catalyst or irradiation, polyolefin can undergo chemical reactions to form materials with good performance, such as polyethylene (PE), which can be crosslinked with crosslinking agents (such as peroxides) to produce PE materials with good performance. Waste polyolefin can be chlorinated, and the chlorinated polyolefin can be used in binders and coatings. In addition, polymer polymerization to make oil is a common cycle method.

3.       Hybrid polymers and composites

A common method of making use of a variety of polymer mixtures is cracking them to make oil. The mixture is cracked at high temperatures to produce gas and oil, which can be used as fuel or refined directly at the refinery. Chemical plants have high requirements on the organochlorine content of oil, generally no more than 10 * 10-6. However, the organochlorine content of oil obtained from cracking of plastic mixture can reach (50 to 200) * 10-6, so it is very important to dehalogen before cracking or during cracking. In addition, waste plastics often contain heavy metal element compounds, cracking oil refining to consider the poisoning of the catalyst. Most of the resins of composite materials are thermosetting resins such as unsaturated polyvinegar resin, epoxy resin and phenolic resin, etc. The waste materials of composite materials are not only used as powder filler, combustion to take heat and chemical auxiliary fuel, but also used for cracking and recycling oil products and raw materials. For example, after the decomposition of glass fiber reinforced plastics at 380 ℃ at atmospheric pressure of 50 ℃, the further decomposition at 450 ℃ and 550 ℃ can obtain oil products. Due to the large amount of residue, a special decomposition furnace needs to be designed to complete the pyrolysis process, and the research work is still under way. Another example is the pyrolysis of phenolic resin in the experimental vulcanization bed (722 ℃), the products include aliphatic hydrocarbon (mass fraction is 5 · 24%), phenol (8, 25%), carbon black (42).2%), gas (24, 3%), etc.

Chemical cycle process and equipment

1.       Reaction Still

Reaction kettle is a common chemical equipment for chemical circulation, and its matching equipment is condenser, storage tank, distillation tower, etc. The products of raw materials (such as polyolefin) degraded in the reaction kettle can be monomer, chemical raw materials, etc., such as PET pyrolysis and then polymerization into PET, or unsaturated polyvinegar resin can be produced. According to the demand, the reactor can be designed into a tank reactor to facilitate heating and slag removal. The reactor can also be designed as a tubular reactor, which can increase the cracking temperature, shorten the time, and continuously crack, suitable for the cracking of ps, PMMA and other polymers.

2.       Fluidized bed reactor

Fluidized bed reactor is a kind of bed reactor. W. kanaminsky et al., Germany, used propane combustion to heat carrier gas or water vapor, and used heater to heat sand and carrier gas to 500 ° c at 00 ° c. The carrier gas should be enough to promote sand fluidization in the reactor. The polymer is squeezed into the fluidized bed by the extruder, and the polymer material is cracked in the fluidized bed. The resulting gas and carrier gas are separated by condensation and separation, and the pyrolysis products are obtained. Fluidized bed cracking apparatus has the advantages of fast heating, high efficiency, even cracking temperature and closed system. Cracking reaction is best carried out under inert carrier gas. If air is used as carrier gas, the product is easy to be oxidized and the thermal energy of the obtained oil is 10700 lower.

3.       Extrusion cracking equipment

Extrusion cracking equipment is composed of two extruders in series. The first extruder has a vent hole. The waste polymer materials were cracked at low temperature on the first extruder. The main purpose was to remove HCI from the waste materials. The intermediate products of cracking are then entered into the second extruder for high-temperature cracking, which turns the polymer into a low-molecular compound or oil or gas. After separation, HCG cracking reaction can be carried out continuously, which can be decomposed mechanically and thermally. In addition, new devices are being researched and developed.

Reclamation and Re-resource Of Fiber Reinforced Polymer Based Composites

1.       Mposition and recycling of fiber reinforced resin matrix composites

1.1   Thermoplastic resin base

Fiber reinforced thermal plastic recycle and pure thermoplastics (FRTP) recycling some similar, but there in the FRTP enhancement phase, and enhance the phase structure and distribution characteristics of greater influence on the performance of the materials, so its recovery processing is much more difficult than pure thermoplastics, and recovery processing after the change of its mechanical properties is also a focus of concern. In the past, high industrial costs and cumbersome recycling processes meant little attention was paid to recycling, resulting in the accumulation of waste fibre-reinforced plastics in factories. With the intensification of business competition, the enhancement of environmental protection awareness and the pressure of resource depletion globally, more and more factories have processed and recycled their wastes, and great progress has been made in the recycling and utilization of fiber-reinforced plastics internationally.

1.2 Thermosetting resin base

In contrast, the separation and recovery of fiber reinforced thermosetting resin matrix composites is more difficult due to the three-dimensional network structure formed after molding. According to the recovery process, there are two methods: one recovery and three recovery. Secondary recycling refers to the use of waste materials to be mechanically crushed, used as a filler for the preparation of new composite materials, or directly used to fill thermoplastics. This process only requires mechanical action and is a physical change process. The three times recovery method means that the thermosetting resin matrix is decomposed into its low molecular substance by heating it in different media or through chemical reaction, so as to achieve the separation from the reinforcing material and realize the purpose of recovery.

A granulator is used to granulate the chip molding (SMC) fragments. The glass fiber in the granule still has the basic size (the fiber length-diameter ratio is greater than the critical value) and filling into the plastic has a reinforcing effect. In addition to the mechanical recovery of unsaturated polyester SMC, thermosetting phenolics are also commonly recovered by this method. During the crushing process, the fiber is separated from the brittle epoxy resin matrix to obtain a mixture of particles and staple fibers, and then the secondary pulverized particles are recycled according to different particle sizes and fiber lengths through screening or air separation. The results showed that the mechanical properties of long fiber reinforced plastics were improved by adding recycled materials in PA6.

The decomposition of polymer materials by supercritical fluid is a new technology developed in recent years, especially in thermosetting plastics. The liquid phase consists of medium and low molecular weight organic materials, and the solid phase is fiber. The obtained fiber has no obvious difference compared with unused fiber after electron microscope observation, and there is no organic material on the fiber surface, so it can be used again as reinforcing material. Studied the decomposition and recycling of carbon fiber/phenolic composite materials, and found that in the supercritical water reaction medium system in alkaline environment, increasing temperature, prolongation of time and increasing alkali concentration would be beneficial to the decomposition of resin matrix.

2.       Separation and recycling of fiber reinforced rubber matrix composites

Short fiber reinforced rubber composite (SFRC) is an important part of rubber products. The main recycling ways of waste SFRC are to produce recycled rubber and waste rubber powder. Taking tires as an example, at the end of the 20th century, the world produced more than 10,000,000 tons of waste tires every year, and our country was close to 10,000,000 tons of waste tires. In the process of producing recycled rubber from waste tires or other waste rubber products, at least 5 waste fibers were generally produced, and the output was very considerable. For environmental protection and security needs, most of the reclaimed rubber factory installed with waste fiber recycling equipment, but due to technical or economic reasons, such as waste fibers were used as the fuel burn more, make the fiber more than on attached vulcanized rubber produces a large number of our fleet and s02 gas, serious atmospheric pollution and the surrounding environment, and can make the fiber of recycling waste materials.

Fortunately, people have paid more attention to the research and application of this field. An earlier overseas for recycling waste fiber, carrying out the work are mainly concentrated in the field of building materials and rubber, synthetic fiber cord scrap filling on the coagulation of the tensile strength, impact strength and tensile strength increased, and the craft simple, the cost is not high, when used as waterproof tarpaulins, runway pavement materials, not only reduce the cost, and can improve the tensile strength and resistance to puncture strength. The experiment shows that although the waste rubber has been damaged to some extent during the regeneration process, it still has certain mechanical strength, especially synthetic fiber, which still has the characteristics of good elasticity, high abrasion resistance and excellent dielectric resistance. Although the surface of these waste fibers is coated with broken rubber residue and rubber powder, their potential utilization value can be fully developed through proper processing.

Polymer material mixing extrusion technology and complete equipment

Mixing extrusion process is the only way for polymer materials, especially plastics, to move from products to industrialization. Modern polymer materials are developing towards high-performance polymer structural materials, new polymer functional materials and general polymer materials with low cost and high performance. 

High performance polymer structural materials are characterized by high specific strength, excellent corrosion resistance, abrasion resistance and easy processing, which are of great significance to the development of national economy and national security. Due to its unique functional and special type, new polymer functional materials have been widely used in the industrial fields such as ecological environment protection, information functionalization, biomedical equipment, material separation membrane, energy conversion and energy storage technology. High performance of general polymer materials and low cost of engineering plastics are still the focus of current research and development of polymer materials and an important measure to expand the application scope of general plastics and engineering plastics.

In addition to some processing properties of traditional polymer materials, the new polymer materials have many differences in physical and chemical properties. Appeared with the development of new polymeric materials, the fields of application broadening, to high polymer material mixing extrusion are also put forward higher request, the traditional mixing technology and equipment have not well some new high polymer material to meet the demand of the mixing, therefore, the development of new type mixing extrusion technology and equipment, to meet the needs of the new polymer materials to industrialization, mixing equipment BNR; at the same time, also is inevitable trend of the development of polymer processing equipment today.

1.       Application of twin screw mixing extrusion technology

Modern mixing and mixing extrusion technology is to blend existing polymer materials with a variety of polymers or add other materials to optimize the combination of different materials, so as to significantly improve the material properties, or give raw materials with new properties, adding new varieties to the polymer family. In the whole plastics industry, about 60% of the plastics have to be mixed and modified to produce new materials. Most of these complex processing processes are completed in the mixing equipment represented by the twin screw extruder. Using the same direction twin screw to mix extrusion has the following advantages:

(1) excellent mixing and plasticizing performance, which can fully guarantee the dispersion uniformity and performance uniformity of various materials after mixing, and is suitable for complex operations such as filling, blending, glass fiber reinforcement, reactive extrusion and volatile removal of various resins and plastics.

(2) cylinder and screw can realize "building block" combination, so as to achieve multi-purpose, multi-function.

(3) screw meshing, self-cleaning effect is good; The material achieves superior surface renewal effect and excellent exhaust performance, which can eliminate the gas or monomer generated in the mixing and plasticizing process.

(4) high screw speed, large production capacity, low power consumption per unit production, obvious energy saving effect.

Based on the above advantages, the co-directional twin-screw mixing extrusion technology has an irreplaceable advantage in polymer material processing equipment and occupies a leading position in polymer material modification production.

At present, the new type twin-screw compounding and the latest application of extrusion technology is mainly manifested in the following aspects: the preparation of nanometer material modification is high polymer material rigid Gao Ren type of low cost, high polymer alloy materials, electromagnetic shielding polymeric materials, novel polymer materials for degradable plastics, electronic packaging, new masterbatch and various functional masterbatch, etc., can also be used to new composite materials (such as wood plastic composite) the production and preparation of new materials, in addition, can also be used for polymer grafting, polycondensation of reactive extrusion. The industries involved include household appliances, automobiles, communications, electronic technology, national defense, aerospace, environmental protection, chemical industry, building materials, electric power, etc.

2.       Development of new polymer material extrusion technology with twin screw

At present, the development direction of new polymer materials, which are mainly composed of nanomaterials, degradable plastics, modified asphalt and wood-plastic composite materials, centers on the industrialization of these materials, and the same-direction twin-screw extrusion technology becomes the key to realize the industrialization. Compared with ordinary polyolefin materials, these materials have great differences in material system composition, molecular structure and rheological properties.

(1)     Nanomaterials are becoming a new type of materials developed by various countries in the world. From the preparation of nanometer masterbatch to the production of nanometer modified plastics, twin-screw extruder plays an irreplaceable role in the industrialization of nanometer plastics. Firstly, due to the particle size distribution of nanomaterials, the mixing extrusion and dispersion effects are required to be high. Secondly, the preparation of nanometer masterbatch for inviscid melt characteristics, low toughness, contains a large amount of gas extrusion and additives in the process of removing products of decomposition, and the traditional polymer under different state of plasticizing characteristics such as high brittleness, cooling and finished product process is different from ordinary polyolefin masterbatch process. 

     From mixing and plasticizing extruder to cooling and granulation, many innovative developments are needed. Therefore, the general cooling method of molten polymer cannot be adopted. The final product is produced by adopting the closed feeding mode with powder collection, adopting the new high-efficiency dense rotor element in the screw, setting buffer type exhaust mode in the cylinder, and adopting the route of belt conveying and cooling, pre-crushing and crushing in the material strip cooling and crushing.

(2)     There are a lot of starch in the development of starch filled degradable plastics, double degradable plastics and whole starch thermoplastic plastics. In addition to plasticizing and mixing them, exhaust dehydration and residence time distribution in the extrusion process have become problems that need to be solved when mixing and granulating. Therefore, according to the specific materials, the appropriate host screw length-diameter ratio, exhaust location and quantity, screw structure and arrangement, additive adding mode and adding point should be selected to test and determine the configuration; At the same time, the operation technology and technology also become the key problem of the degradation plastic twin-screw extrusion. The above key technologies can be based on the existing successful experience, combined with extrusion process experiment and results analysis, finally determine the extrusion process equipment configuration.

(3)     Modified asphalt has become a new direction of polymer material modification. Focusing on its application in highway construction, airport reconstruction and expansion projects, improving its temperature resistance and low temperature brittle property is the main direction of improving its application value. Because of the extensive molecular weight distribution and the structure of macromolecule, the modification of asphalt has not been much improved. Modified asphalt is very special, has both belong to the characteristics of the rubber plastic blending, but also has the content of the product post-processing, transport of twin screw extruder, mixing elements of development, such as extrusion granulation are put forward new requirements, need innovation to develop new type structure and configuration of the screw element, console, selected double screw part in all kinds of test parameters, such as screw length to diameter ratio, number and position of exhaust section, shear rate, extruding form and structure, etc.

(4)     In terms of material science, WPC is a new material with great potential. It is reported that plant fiber composites have been widely used in automobile industry, construction industry, transportation industry, aviation industry and so on due to their high mechanical properties, specific hardness, specific strength, sound absorption and biodegradability. In wood fiber, wood powder mixed with resin matrix, the mixture of different methods of wood fiber in composite material obtained by dispersing uniformity of difference is very big, to realize the industrialization of the wood plastic composite this new material production is the key to the extrusion process and special structure form of extruder, the technology innovation point lies in the segmented charging ways, special screw type structure, TME and ZME element, high torque gear transmission system, large screw length to diameter ratio and D/Di = 1.55 free volume, the one-step method of twin-screw extrusion production.

Development and application of degradable polymer plastics

Development and application of biodegradable polymer plastics, biodegradable plastics is a kind of new type with the function of degradation of polymer materials, in use process, it has to do with the same kind of common plastic with the corresponding health and relevant application performance, and after its complete function, the material can rapidly degraded in the natural environment conditions become easy to be given environment fragments or crushed, and with the passage of time further degradation become eventually oxidation products (CO2 and water), return to nature. 

Based on the environmental pollution caused by plastic waste, as well as the demand of environmental protection and human needs, it is urgent to study degradable polymer materials. In a specific time and under certain environmental conditions, the chemical structure of biodegradable plastics will change. According to the reasons for the changes in its chemical structure, biodegradable plastics can be divided into two categories: biodegradable plastics and photodegradable plastics.

1.     Degradation mechanism of degradable plastics

Generally speaking, degradable plastic refers to a kind of plastic that can be decomposed into small molecules through the action of microorganisms in soil or solar radiation.It must meet the requirements of the use of products and easy to process on the basis of the basis of biodegradable properties. The nature of the action of sunlight on polymer materials is the comprehensive effect of ultraviolet light in sunlight and oxygen in air, so it is also called photooxidation degradation. Take polyolefin as an example to explain the mechanism of photooxidation degradation. In essence, photooxidation causes chain breaking or crosslinking of polymers, and some oxygen-containing functional groups, such as carboxylic acids, peroxides, ketones and alcohols, are formed in this process. Catalyst residues in polymers and initiation of peroxide and carboxyl groups introduced during processing are the main sources of degradation.

Under the action of microorganisms (mainly fungi, bacteria or algae, etc.), polymers can be eroded or metabolized to cause changes in their chemical structure and decrease in molecular weight. The mechanism of action can be mainly divided into two situations :

(1) biophysical action. That is, after the erosion of plastic products by microorganisms, biological cells growth, promote the decomposition of polymers, ionization or proton, this physical action on the polymer caused mechanical damage, the high molecular weight of the polymer into oligomer fragments, so as to achieve the purpose of physical degradation.

(2) biochemical action -- direct action of enzymes. This situation is caused by the erosion of enzymes secreted by fungi or bacteria, which leads to the splitting or oxidative disintegration of plastics, and causes the splitting or oxidative degradation of insoluble polymers into water-soluble fragments, generating new small molecular compounds (CH4, CO2 and H2O) until the final decomposition.

There are generally two hypotheses about the mechanism of biodegradation of polymer materials that lead to biodegradation. The other is an invasive cut from the end of the chain. Therefore, the structural properties of materials, such as composition, main and side chain structure, size of end groups, and presence or absence of spatial steric resistance, are the key factors affecting their degradation performance. Among them, the main chain properties have a greater impact. If the main chain of the polymer contains bonds that are easily hydrolyzed, it will be easily biodegraded. Secondly, if the backbone is flexible, the degradation rate will be relatively fast, whereas if the backbone is rigid and orderly, the degradation rate will be slow. 

The biodegradability of polymer materials is reduced by branching and crosslinking. For example, the introduction of hydrophobic groups at the end of polylactic acid (PLA) molecular chain can reduce the erosion rate at the initial stage of degradation. This is because in the original degradation process, PLA's erosion mainly depends on the structure of molecular chain end, and the addition of hydrophobic groups leads to the decline of its erosion rate. In addition, some researchers have studied the chemical structure of polymers and the relative molecular weight of materials that play an important role in their degradation.

2.    Development of biodegradable plastics

The development direction of biodegradable plastics in the future can be as follows:

(1) biodegradable plastics were prepared by studying the biodegradation mechanism of degradable polymers, and the block copolymerization of biodegradable plastics with existing ordinary polymers, microbial polymers and natural polymers was studied and developed.

(2) to search for microorganisms that can produce polymer plastics, explore new polymers, analyze their synthesis mechanism in detail, improve their productivity through existing methods and genetic engineering methods, and study efficient methods of cultivating microorganisms.

(3) pay attention to the control of degradation rate, develop efficient degradation promoters and stabilizers to improve the biodegradation performance of degradable plastics, reduce their cost, and expand the market application.

(4) research and establish a unified definition of degradable plastics, enrich and improve the evaluation method of biodegradation, and further understand the degradation mechanism.

What are the characteristics of Polymer PTFE Capillary Tube?

1.    Main characteristics of Ptfe teflon capillary tube

(1).Very low friction coefficient: its friction coefficient is generally only 0.04, is a very excellent self-lubricating material, and the friction coefficient does not change with the temperature.

(2). High chemical stability: it can withstand all strong acids, including aqua regia, hydrofluoric acid, concentrated hydrochloric acid, nitric acid, fuming sulfuric acid, organic acid, strong alkali, strong oxidant, reducing agent and various organic solvents. Very suitable for high purity chemical feeding.

(3). Good anti - viscosity, tube wall is not easy to adhere to colloid and chemicals.

(4). Excellent electrical insulation performance: PTFE is a highly nonpolar material with good dielectric properties and great resistance. Its dielectric constant is about 2.0, which is the smallest among all electrical insulation products.

(5).Flexible and flexible.

(6).Good anti - viscosity, tube wall is not easy to adhere to colloid and chemicals.

(7).Part of the tube transparency, easy to observe the internal fluid status.

2.  Polymer Ptfe capillary molding process

Ptfe capillary tube is a special pipe made by drying, high temperature sintering and finalizing after mixing ptfe dispersion resin and propellant, and then subjected to certain shearing force in the mouth mold with cone Angle.

Ptfe capillaries are extremely fine, forming a set of independent general specifications according to its use. Also may according to the different need, makes the black capillary tube, the white capillary tube, the yellow capillary tube, the red capillary tube and the transparent capillary tube and so on, generally is blue or the black reel packing.

3. Use of ptfe teflon capillary tube

    It is widely used in chemical industry, chlor-alkali industry, machinery, automobile, electric heating pipe, pulp, steam, compressed gas, heat exchanger, coating, textile, pharmaceutical, medicine, bicycle industry, coffee machine and other industries, mainly used as catheter.

In addition can also use fep (PVF and six f propylene copolymer) made of transparent tube, its basic retain the performance of ptfe, such as: excellent high and low temperature resistance, chemical stability, electrical insulation, prominent not sticky and high mechanical strength, only on the high temperature limit 50 ℃ lower than the ptfe. But it is more flexible and transparent than ptfe, making it easier to see what's going on inside as it transports liquids and gases.

Polymer PTFE production process Ram-punch extrusion

With the development of technology and economy, ptfe has been applied in more and more fields, and has become an indispensable material to solve many key technologies in scientific research, military and civil fields and improve the production technology level. In order to continuously improve the production efficiency of polymer ptfe, we began to adopt the advanced production process, which is suitable for high viscoelastic material —— Ram-punch extrusion.

According to the principle of "forging", plunger stamping extruder mainly adopts plunger with small cross section area and high frequency stamping to push material into the barrel of extruder. Compared with traditional hydraulic column extruder, it has the characteristics of high stamping frequency, good melt plasticizing effect, good product quality, simple equipment and process.

According to the forming characteristics of Ram-punch extruder, the extrusion process is analyzed and studied. The physical model of the whole extrusion process of plunger ram extruder is established, which is divided into five sections: solid feeding section, melting section, shunt section, forming section and cooling section. The influence of die length and pressure vibration frequency on extrusion process was analyzed. Analysis results indicate that: although there are large fluctuation of pressure at the entrance of the melt, but on the whole pressure from inlet to outlet were reduced gradually, thus ensure the enough pressure to push the material extrusion, and the closer it gets to the finish mold outlet pressure and speed fluctuation is smaller, so it can ensure the continuity of extrusion, finally get good quality products. The length and stamping frequency of the die have certain influences on the extrusion pressure and speed. Due to the high viscosity of PTFE, a longer die should be selected, and the stamping frequency between 5-6hz is appropriate.

Ram plunger extrusion machining polymer PTFE are very new machining method , but in the process of material forming process, also cannot leave the material flow and deformation, rheological behavior and the law, understanding the process of molding process of reasonable selection, operation and optimization control and improve molding equipment has very important practical significance. Plunger stamping is not a steady-state machining method, and there is vibration in the stamping process. It is of great significance to study the behavior response of polymer under the action of vibration field, and to discuss how much impact the vibration field will have on the flow stability, so as to study the dynamic forming of polymer materials and optimize production.

Polymer micro-mechanical mold assembly molding

In-mold assembly molding of polymer micromachines is a new technology in which technological bottlenecks of micromachines micro-assembly manufacturing process can be effectively solved,  however, the thermal-fluid-solid coupling effect between polymer  high temperature viscoelastic melt flow and preformed micro solid part can be caused which induces preformed micro solid part producing frequently the thermal-fluid-solid coupling deformation and  necking fusing fracture phenomenon, how accurate control and predict thermal-fluid-solid coupling deformation and necking fusing fracture phenomenon is key scientific issues of in mold micro assembly molding technology industrialized application.

Therefore, based on the developed variable combination  mold and Auto model FB-110C polymer co-injection molding machine, the polymer micromachines In-mold assembly molding experimental research platform was established, by which the influencing rule and influencing mechanism of process parameters and properties of polymeric materials on preformed micro shaft thermal-fluid-solid coupling deformation and necking fusing fracture phenomenon were  systematically studied, key regulatory parameters of thermal-fluid-solid coupling deformation and necking fusing fracture phenomenon in in-mold micro assembly molding process was clarified; the scientific foundation of the research and development of thermal-fluid-solid coupling deformation precision-shaped control technology  and the  prevention technology of necking fusing fracture phenomenon was laid. The main innovations and achievements as follows.

The variable combination mold of  typical micro mobile motion pair in-mold micro assembly molding was developed, and Based on the developed variable combination  mold and Auto model FB-110C polymer co-injection molding machine, the polymer micromachines In-mold assembly molding experimental research platform was established.

The influencing rule and influencing mechanism of secondary molding melt injection temperature, secondary molding melt injection pressure  and  screw stroke on necking fusing fracture phenomenon of preformed micro shaft, the research results show  key regulatory parameter of preformed micro shaft necking fusing fracture phenomenon is secondary molding melt injection volume,  when the secondary molding melt injection volume exceeds its critical melt injection volume, the critical melt injection volume of induced preformed micro shaft necking fusing fracture phenomenon depends on secondary molding melt injection temperature, which is positively proportional to secondary molding melt injection temperature. Improving of secondary molding melt injection temperature will help improve the critical melt injection volume of induced preformed micro shaft necking fusing fracture phenomenon, which increase the secondary molded part density and strength in In-mold assembly molding process, at the same time, but also to avoid preformed micro shaft necking fusing fracture phenomenon.

Experimental research results show that the micro shaft unidirectional necking fusing fracture phenomenon possible ways  have two main factors, firstly, the axial tensile force is too large; secondly, the preformed micro shaft near-surface temperature in a secondary molding process  is too large, which led to partial melting  and a sharp decline of elastic modulus. The heat transforms time contact between secondary molding high temperature and preformed micro shaft will prolong with increasing of secondary molding melt injection volume, which make the preformed micro shaft near-surface temperature improve with increasing of screw stroke.

 When the preform micro shaft near-surface temperature exceeds the glass transition temperature, local micro assembly interface of preformed micro shaft will experience continuous phase transition evolution from elastoplastic solid state to viscoelastic plasticity glassy state ,final to viscoelastic high-elastic state, which led to a sharp decline of elastic modulus and make polymer material in local phase transition evolution region lost the ability to resist deformation, preformed micro shaft in local phase transition evolution region of micro assembly interface must produce necking phenomenon under tensile force effect.

When the tension force reaches a certain level, preformed micro shaft will produce the necking fusing fracture phenomenon. In order to preform micro shaft near-surface temperature does not exceed the glass transition temperature, which requires its secondary molding melt injection volume does not exceed the critical injection volume. Based on above necking fusing fracture mechanism, the preparatory proposed necking fusing fracture mechanism theory and prevention technical method of preformed micro shaft necking fusing fracture provide technical support for the industrialized application of In-mold micro assembly molding technology.

Experimental research results show that the preformed micro shaft thermal-fluid-solid coupling deformation depends on secondary molding melt injection temperature，secondary molding melt injection pressure ，secondary molding melt injection volume and preformed micro shaft material properties，and the process parameters affect its thermal-fluid-solid coupling deformation  by adjusting pre-formed micro shaft micro assembly interface to withstand the impact of the thermal-fluid-solid coupling pressure, viscoelastic supporting normal stress, viscous friction drag shear stress and micro shaft stiffness against deformation，the preformed micro shaft thermal-fluid-solid coupling deformation increase with increasing of secondary molding melt injection temperature，secondary molding melt injection pressure, secondary molding melt injection volume, and based on key regulatory parameters of viscoelastic supporting normal stress, viscous friction drag shear stress and micro shaft stiffness against deformation, the formation mechanism of preformed micro shaft thermal-fluid-solid coupling deformation was revealed.

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Measurement for shear viscosity spectrum of polymer melts by using screw extruder capillary

Most polymer materials are processed in the melt state, which involves melt flow and deformation, which not only affects the processing process itself, but also affects the final performance of the product. Therefore, the study of rheological properties of polymer materials has been a hot topic. Accurate measurement of rheological parameters is the basis of in-depth study of rheological properties.

Shear viscosity is an important parameter to characterize the rheological behavior. The so-called shear viscosity of polymer melt is the ratio of shear stress and shear rate that melt is subjected to in the process of flow. Polymer melt causes pseudoplastic fluid, and its flow behavior has the characteristics of shear thinning. It is usually necessary to use the relationship curve between shear viscosity and shear rate, namely shear viscosity spectrum, to fully reflect the processing characteristics of polymer melt.

The basic method of measuring melt viscosity is to try to make the melt flow through a long and thin capillary tube, such as a round capillary tube. The shear stress can be calculated by measuring the pressure drop at both ends of the melt as it flows through the capillary tube. The shear rate can be calculated by measuring the flux of melt per unit time. Thus the melt viscosity can be obtained.

The conventional way to get the melt out of the capillary tube is to use piston propulsion. The advantage of this method is that it USES fewer test materials and can obtain higher shear stress. The high pressure capillary rheometer is based on this principle [4].However, the disadvantage of this test method is that the material cannot be tested under the actual processing conditions, and it is difficult to obtain the rheological properties of the polymer melt when it is processed. Especially in the study of blending modification of several polymer materials, the polymer melt needs the strong shearing action of screw to achieve the purpose of blending. High pressure capillary rheometer is not suitable for testing such materials.

The screw extrusion capillary rheological test device can solve the above problems. The device USES the propulsive force of the screw to make the polymer melt flow through the capillary tube. Therefore, the shear viscosity of polymer melt can be measured under conditions closer to real processing. This method is particularly suitable for the measurement of the rheological properties of thermoplastic materials and their mixtures. Because the measurement simulates the real experimental environment, the obtained test parameters can more accurately describe the behavior of materials in actual processing.

Shear viscosity spectra of polymer melts can be measured using specialized test instruments, such as high pressure capillary rheometers, or combined revolutions. However, these devices are expensive and limited in practical use, especially in the application of large-scale industrial production. In fact, it is not necessary to rely on the special test instrument, as long as the shear viscosity test principle, you can use a simple small single-screw extruder and capillary mold, constitute a low-cost shear viscosity spectrum test device. Combined with computer data processing, the shear viscosity spectrum of polymer melt can be easily and quickly obtained. This method is especially suitable for small and medium-sized enterprises to carry out product development and raw material inspection.

Polymer plasticized compounding extruder screw design

Screw is the most important part of extruder, can be said to be the heart of the extruder, it can directly affect the application of the extruder and production efficiency. The performance of screw determines the productivity, plasticizing quality, dispersion of filler, melt temperature and power consumption of an extruder. Through the screw rotation, the polymer plastic can be extruded, and the plastic can move, pressurize and obtain some heat from friction in the cylinder. During the movement of the cylinder, the plastic can be mixed and plasticized.

1.     The screw structure of polymer plasticizing and mixing extruder.

During processing, when the material moves forward along the screw, it experiences changes in temperature, pressure, viscosity, etc., which are different within the full length range of the screw. There are three physical states of   polymer plastic in extruder: glass state, high elastic state and viscous flow state. In order to adapt to the requirements of different states and according to the changing characteristics of the material, the screw can be divided into three sections: feed section, compress section and homogenize section.

The function of the feeding section is to feed the material supplied by the hopper to the compression section. During the movement of the plastic, it generally remains a solid state and partially melts due to heat. The length of the feeding section varies with the type of plastic. Compression section (transfer section) is the role of physical material pressure, so that the material from solid into molten, well out of the air in the material; In order to adapt to the characteristics of reducing the volume when pushing the gas in the material back to the feeding section, pressing the material and melting the material, the screw in this section should produce greater shearing effect and compression of the plastic. 

The function of the homogenizing section (metering section) is to feed the molten material to the machine head at constant volume (volume) and pressure so that it is formed in the mouth mold. The volume of the spiral groove in the homogenizing section is the same as that in the feeding section.

In order to avoid material retention in the end of the screw head dead corner, causing decomposition, screw head is often designed into a cone or semicircle; Some screw homogenization section is - the surface is completely smooth body called torpedo head, but there are also engraved grooves or milling patterns. The torpedo head has the function of stirring and controlling the material, eliminating pulsating (pulsating) phenomenon in the flow, reducing the thickness of the material layer with increasing the pressure of the material, improving the heating condition, and further improving the screw plasticizing efficiency. 

According to melt transport theory, melt flows in the screw homogenization section in four forms, and the flow of molten material in the screw groove is a combination of these four flows: positive flow -- plastic melt flows between the cylinder and the screw in the direction of the screw groove toward the machine head. Counter-current flow direction is opposite to the positive flow, which is caused by the pressure gradient caused by the resistance of the nose, porous plate and filter plate. The flow of the melt in a direction perpendicular to the thread wall affects the mixing and heat exchange of the melt during extrusion. Leakage flow - a backflow formed by the pressure gradient between the screw and the cylinder, along the axial direction of the screw. Different flow patterns have important effects on the mixing uniformity of polymers.

Screw diameter and the determination of structural form, mainly according to the production of product output, specifications, types of processed materials and various structural screw characteristics to determine. Generally, the feeding section of the screw has a deeper groove and the groove depth is unchanged, compression section (melt section) of the screw groove depth along the direction of discharge from the deep to shallow, metering section (homogenized section) of the screw has a shallow groove and the groove depth is unchanged.

2.     The screw material.

Screw is the key part of extruder, as the material of screw must have high temperature resistance, wear resistance, corrosion resistance, high strength and other characteristics, at the same time should have good cutting performance, heat treatment residual stress, small thermal deformation and other characteristics. For extruder screw material, there are specific requirements as follows:

(1)   High mechanical properties. To have enough strength, to adapt to high temperature, high pressure working conditions, improve the service life of the screw.

(2)   Good machining performance. Good machining performance and heat treatment performance.

(3)   Good corrosion and wear resistance.

(4)   Easy to draw.