Plasticization is the process of incorporating additives into the extrusion of polymers and plastics to make them flexible and bendable. The PVC foam board production line utilizes the plasticization process to add other superior properties like flame retardancy to the final extrusion products. Plasticization and the extruder screw go hand in hand. Remember, the entire plasticization process happens in the extruder screw. Apart from the extruder crew, other factors impact the quality of plasticization. That is what we are going to focus on in our article today. Other than that, we will take a closer look at plasticizers, what they are, and how they work. We will also highlight how to choose the ideal plasticizer for your PVC foam board production line.
Plasticizers in the PVC foam board production line
They are non-volatile substances incorporated in processing elastomers and plastics. The intention of doing so is to improve the polymer’s processability, extensibility, and flexibility. Apart from that, their function is to heighten the thermoplasticity and enhance the flow of polymers by reducing the melting temperature of the polymer. Along with lowering the melting temperature, plasticizers also lower the glass transition temperature and elastic modulus of relevant after product under extrusion without necessarily changing the basic chemical features of the said plasticized product.
In other words, a plasticizer is an additive that is either an odorless or colorless ester meant to amplify the elasticity of PVC and other extrusion materials. The plasticizer helps in producing unplasticized PVC or rigid PVC. The two find application in the making of window profiles, foam boards, siding, and pipes. On the other hand, you can use plasticizers to process plasticized PVC or flexible PVC. Flexible PVC and plasticized PVC come in handy when making roofing, flooring, PVC films, and cables.
Their cheap nature and ready availability make them a favorite for the PVC foam board production line. Plasticizers make PVC soft, bendable, and flexible. They are also useful in increasing the durability of PVC products. In the absence of plasticizers, all PVC products would be rigid.
How are plasticizers used in the PVC foam board production line?
Plasticizers are essentially organic solids and liquids utilized in the extrusion of plastic products to help with the melting process. They enhance molecular mobility when mixed with compatible polymers. Plasticizers also help to reduce the interaction and reaction between molecules. As much as numerous theories can help us break down this concept, the underlying point is that plasticizers cut down on the chain attractions that happen from polymer to polymer. Moving on, it is important to highlight the fact that the extent of plasticization a plasticizer can offer relies on its chemical structure. The chemical structure of a plasticizer involves its functional groups, molecular weight, and chemical composition.
If a plasticizer has a small number of polar groups or it has a low molecular weight, it should provide better plasticization. The plasticizer should also generate a higher degree of flexibility. However, plasticizers with low molecular weight have one big drawback. Low molecular weight causes vocalization problems and an increased likelihood of migration which could come with a significant safety risk. That, aside, you can potentially plasticize every kind of polymer. Nonetheless, the preferred plasticizer ought to be compatible with the underlying polymer for optimal results.
What factors affect the quality of plasticization?
1. Extruder screw speed
The velocity of the extruder screw has a huge impact on the quality of the plasticization of the resin. The speed of the extruder screw impacts the plastic shear within the spiral groove. The small extruders screw groove is relatively shallow. Therefore, heat from the heat source will be absorbed a lot faster. As a result, increased heat enhances a hasty softening of the plastic material within the compression compartment. The section between the barrel wall and the screw produces very minimal friction-related heat energy. Low frictional heat energy promotes high-speed rotation which in turn amplifies the resultant plasticizing capacity.
On the other hand, to prevent the production of extreme frictional heat that could trigger uneven plasticization, the bigger extruder screw should not be rotating so fast. Likewise, do not process heat-sensitive plastics at high screw speed. Heat-sensitive resins tend to decompose easily under such conditions.
As much as every screw size features a specific speed range, the average running speed of an ideal screw should be between 100 RPM and 150 RPM. Of course, smaller screws will rotate at a faster speed in comparison to their bigger counterparts. Remember, if the screw rotation speed is too slow, the plastic resin will not melt appropriately. On the other hand, excessive screw speed will scorch the plastic resin.
2. Extruder screw back pressure
By amplifying the back pressure of an extruder screw you can heighten the performance of the extruder screw when processing molten resin. Similarly, the strategic move will get rid of any plastic particles that are unmelted. It will also boost the uniformity of all raw materials within the barrel in addition to heightening the resin’s density.
To boost the temperature or heat conditions in the barrel, you need to increase the backpressure as well. Backpressure has a significant impact on the extrusion process. Nonetheless, there are negative consequences if the backpressure is too much. Hastened decomposition of heat-sensitive plastics increases the backpressure. In addition to that, too much back pressure promotes salivation for plastics with low viscosity.
On the other side of the coin, when the back pressure happens to be extremely low, the extrusion end product is likely to come out with defects like bubbles or yellowed surfaces.
3. Compression ratio
The compression ratio is the ratio of the exact depth of the last extruder’s screw groove within the feeding component to the precise depth of the metering section’s first groove. The compression ratio affects the backflow and filling degree as well as the plastic compressibility impact. For the compression ratio to take effect, the exhaustion system along with the heat transfer should be okay.
An ideal compression ratio will amplify plastic density by tightly binding the molecules to one another. As a result, tightly bound plastic molecules mitigate air absorption. It also prevents an escalation in temperature because of pressure. Still, the compression ratio has a substantial impact on the output quality. However, an improper compression ratio compromises the plastic’s physical properties.
Moving on, when the extruder screw’s compression ratio increases there is a resultant increase in plastic temperatures within the barrel in the course of the plasticization process. Likewise, a higher compression ratio enhances the plastic mixing uniformity besides reducing the relative output.
Apart from that, an increase in the compression ratio is ideal for plastics that do not melt easily. The same is true for plastics that are thermally stable along with plastics whose melting viscosity is low. On the other hand, the slightly low compression ratio tends to be appropriate for plastics that are heat sensitive or plastics that are fusible. It is also ideal for plastics whose melting viscosity is super high.
4. Length to diameter ratio
The length to diameter ratio involves the ratio of the extruder screw’s functional working length to that of the diameter on the screw component. In case the length to diameter ratio is large, the rate at which the plastic mixes will be uniform. A longer extruder screw is ideal for processing plastics that incorporate good thermal stability. The length of the extruder screw also boosts the mixing performance minus scorching the plastic resin.
Process plastics with poor thermal stability in a screw extruder that is short. Contrarily, process stable high-temperature plastics at a length to the diameter ratio of about 22\24. Similarly, process ordinary plastics at a ratio of about 18\22. Heat-sensitive plastics and high sensitive PU need an extruder screw length to diameter ratio of 17\18. The precise length to diameter ratio of extruding plastic depends on the individual features of the plastic.
5. Metering section
The extruder’s metering section is responsible for about 20% of the working length of the screw. It ensures the total plasticization of plastics by promoting the melting process and guaranteeing uniform temperature within the extruder. The length of the metering section also has an impact on the mixing uniformity of the resin. A longer metering section will essentially allow the resin melt to linger for a longer period allowing for complete plasticization. When the length of the metering section is short, it limits the rate of thermal decomposition.
Consequently, the temperature and the mixing quality will not be uniform. Keep in mind that plastics that are heat sensitive like PVC need to linger in the metering section for an extended period. Ideally, if you aim to extrude PVC, your PVC foam board production line will require a longer metering section. That will aid in mitigating thermal decomposition. To avoid the potential after-effects of plastic thermal decomposition, it is imperative to equip your extruder screw with the appropriate wear resistance features.
6. Screw compression section
Pressurization, compression, and mixing of plastic under extrusion happen within the screw compression compartment. When materials pass through this section, they are supposed to be in molten form. Yet, they may not necessarily have undergone uniform mixing. The compression section allows for a further melting of the raw materials. For this to happen, the groove volume corresponding to the plastic geometrical volume drop ought to be uniform. If that does not happen, the outcome will be poor material pressure along with slow heat transfer. In addition, the aforementioned outcome will also trigger poor exhaust gas.
7. The heating temperature of the extruder screw
It is the melted chilled plastic in the screw and barrel that enables screw rotation. In the same way, the melted resin produces the necessary local heat which facilitates the plastic melting process. Even when heating the PVC foam board extrusion line, it is advisable to set the temperature about 5-10 degrees Celsius below the prevailing melt temperature. You need to keep in mind that a substantial amount of the temperature comes from frictional heat. Nonetheless, several problems come with unregulated melt temperature. That includes wire drawing, condensate, and drooling. The ultimate way to keep the drawbacks in check is to change the nozzle temperature.
Things to consider when choosing the best plasticizer
Compatibility is the measure of how soluble the resin and the plasticizer are when mixed. If the resin and the plasticizer happen to be insoluble, the resultant effect will be a phenomenon called ‘blooming’ or ‘sweating’. That is what happens when the two are not compatible. Hence, compatibility is the first attribute that you need to keep in mind when choosing an ideal plasticizer for your PVC foam board production line. Plasticizers with chlorine tend to be very compatible with resins. Resin/ plasticizer compatibility enhances flame retardancy, durability, and other crucial features of a quality PVC foam board.
A good number of plasticizers tend to include a slight amount of toxicity. The quality of PVC foam boards being extruded is affected negatively by toxic compounds. Even if you choose to utilize a toxic plasticizer, it is vital to control or limit a continuous intake of the said plasticizer. About that, it is advisable to opt for plasticizers with a low amount of toxicity or go for an alternative with no toxicity at all. A good example of a plasticizer that is non-toxic includes chlorinated paraffin. Chlorinated paraffin will blend smoothly with the resin and produce top-quality PVC products.
iii. Flame retardancy
The biggest goal of the plastic extrusion process is to come up with end products of the topmost quality. One of the qualities that make an exceptional PVC foam board is flame retardancy. Flame retardancy means that the product does not catch a flame, which contributes to amplified durability. To achieve that, PVC foam board manufacturers have to make use of plasticizers that enhance flame retardancy. One of such plasticizers is chlorinated paraffin. Essentially, they are paraffin hydrocarbons derived from chlorinated compounds. That makes gives them exceptional flame retardancy and incredibly low volatility.
iv. Mold resistance
Before choosing an ideal plasticizer, it would be prudent to consider the operating environment as well as the performance of the said product. Therefore, it is crucial to factor the two attributes into your decision-making process. Ideally, the plasticizer ought to incorporate antibacterial properties. That will guarantee adequate mold resistance and improve the final quality and longevity of the final products.
v. Electrical insulation
The ultimate plasticization compound must provide unmatched electrical insulation properties. Chlorinated paraffin ticks all the necessary boxes for such a plasticizer. They incorporate low volatility and offer excellent electrical insulation. That explains why they are often utilized as auxiliary plasticizers in large-scale PVC production.
PVC products are often preferred for their lightweight and uncommon durability. For that reason, plastic extruders must choose plasticizers that will grant their products adequate longevity. Nonetheless, the longevity of the preferred plasticizer is linked to its molecular structure and its molecular weight. To attain great durability, it is wise to choose a plasticizer with a molecular weight that is not less than 350.
vii. Aging resistance
Aging resistance and durability go hand in hand. If a plastic product is durable that means that it also has impeccable aging resistance. In essence, the said product does not lose its aesthetic attributes easily. Remember, light, heat, and oxidation accelerate the aging and deterioration of the aesthetic features of a plastic product. In order to guarantee excellent aging resistance, the plasticizer should include heat stabilizers. In addition to that, the plasticizer ought to include light stabilizers and antioxidants as well.
viii. Cold resistance
The chemical structure of a plasticizer determines its cold resistance abilities. Plasticizers that feature cyclic structures significantly minimize cold resistance. It is a result of their poor incompatibility with most resins. Generally, plasticizers that offer great compatibility with most resins hurt the level of cold resistance. For that reason, a lot of cold-resistant plasticizers are hugely utilized as auxiliary plasticizers. Auxiliary plasticizers heighten the cold-resistant capabilities of PVC products. DOA is the representative variety of cold-resistant plasticizers.
ix. Plasticization efficiency
The plasticizing efficiency of a given plasticizer is simply the amount of the plasticizer needed to help a certain resin attain a particular level of softness. Primarily, it is a relative value utilized in comparing the actual plasticizing impacts of different plasticizers.
FAQ About Plasticizers in the PVC Foam Board Production Line
What makes up plasticizers?
Plasticizers are organic liquids or solids created by reacting an acid such as phthalic anhydride or adipic acid with an alcohol. The kind of alcohol utilized in the plasticizer creation process determines the kind of ester created in the end. Essentially, the resultant ester is what we refer to as the plasticizer. Different combinations reacted to come up with a wide range of plasticizers. However, there are very few compounds that can meet the environmental, health, availability, cost, and rigorous performance requirements.
How does internal plasticization happen?
The plasticization process involves altering the chemical structure of a polymer to make it a little more flexible and bendable. On the same note, internal plasticization, applied to rigid polymers, involves chemically changing a monomer or polymer to increase its flexibility.
What kind of plasticizers is used along with polymers?
Numerous types of plasticizers are used to make polymers. Running the PVC foam board production line requires a plasticizer that offers exceptional flexibility along with the ability to operate under high-temperature exposure. PVC-oriented plasticizers include epoxy compounds, trimellitates, polymerics, phosphates, sebacates, glutarates, adipates, and phthalates. Together with that, sebacates and adipates come in handy when the extrusion process requires plasticizers with high molecular weight.
What is a thermoplastic material?
A thermoplastic is a kind of plastic polymer material that is moldable or pliable under certain conditions like an elevated temperature. The thermoplastic also cools and solidifies after cooling. It can also be referred to as a thermosoftneing plastic. There is a major difference between thermosetting polymers or rather thermosets and thermoplastics. While thermoplastics have reversible chemical bonds, thermosetting polymers react to form irreversible chemical bonds under the process referred to as curing.
What effect does plasticization have on water?
Ideally, the plasticization process lowers the viscosity, elastic modulus, and fracture strength of a biopolymer. When water interacts with a plasticizer the outcome is a water mixture along with amplification in the plasticizer content. In simple terms mixing water with a plasticizer will only lead to an increase in the volume of the plasticizer.
What is the purpose of adding plasticizers to plastics?
The main purpose of adding plasticizers to rubber and plastics like PVC is to make them flexible for effortless fabrication and easy handling of extrusion raw materials. Other than that, including additives in the plastics during the extrusion process helps to achieve certain requirements related to the application of the end product such as durability or flame retardancy.
Are plasticizers bad for the environment?
Plasticizers function by minimizing the chemical affinity between molecules of different materials when mixed with plastic material chains. They tend to act as monomers when embedded with polycarbonate plastic. Yet, to be effective, plasticizers are chemically unstable. It is their biggest drawback since their lack of stability makes it easy for plasticizers to leach out of plastic materials and pollute the environment. Phthalate plasticizers in particular are the greatest culprits when it comes to environmental pollution. Not only are they carcinogenic, but they are also known to trigger inflammation and affect the mitochondria.
What is the plasticizing effect?
The plasticization effect involves altering the mechanical and thermal attributes of a particular polymer. Plasticization is achieved by lowering the rigidity of a polymer at room temperature. It also happens by minimizing its melting point making it easy to deform the polymer with minimal force. In the end, a plasticized plastic or rubber product should be flexible and bendable.
Plasticization is an integral part of the PVC foam board extrusion line. Without plasticizers, it would be difficult to process some types of plastics and give them unique attributes that enhance their quality and usability. We hope you now have a better understanding of what plasticizers are and how they react in the extrusion screw.