Properties and Applications of Paraffin wax

Paraffin wax is mostly found as a white, odorless, tasteless, waxy solid, with a typical melting point between about 46 and 68 °C (115 and 154 °F),and a density of around 900 kg/m³.It is insoluble in water, but soluble inether, benzene, and certain esters. Paraffin is unaffected by most common chemical reagents but burns readily.Its heat of combustion is 42 kJ/g.

Paraffin wax is an excellent electrical insulator, with a resistivity of between 10¹³ and 10¹⁷ ohm metre.This is better than nearly all other materials except some plastics (notably Teflon). It is an effective neutron moderator and was used in James Chadwick's 1932 experiments to identify the neutron.

Paraffin wax is an excellent material for storing heat, with a specific heat capacity of 2.14–2.9 J g⁻¹ K⁻¹ (joules per gram kelvin) and a heat of fusion of 200–220 J g⁻¹.This property is exploited in modified drywall for home building material: a certain type of wax (with the right melting point) is infused in the drywall during manufacture so that it melts during the day, absorbing heat, and solidifies again at night, releasing the heat.Paraffin wax phase-change cooling coupled with retractable radiators was used to cool the electronics of the Lunar Rover.Wax expands considerably when it melts and this allows its use in wax element thermostats for industrial, domestic and, particularly, automobile purposes.

 

In industrial applications, it is often useful to modify the crystal properties of the paraffin wax, typically by adding branching to the existing carbon backbone chain. The modification is usually done with additives, such as EVA copolymers, microcrystalline wax, or forms of polyethylene. The branched properties result in a modified paraffin with a higher viscosity, smaller crystalline structure, and modified functional properties. Pure paraffin wax is rarely used for carving original models for casting metal and other materials in the lost wax process, as it is relatively brittle at room temperature and presents the risks of chipping and breakage when worked. Soft and pliable waxes, like beeswax, may be preferred for such sculpture, but "investment casting waxes," often paraffin-based, are expressly formulated for the purpose.

In a pathology laboratory, paraffin wax is used to impregnate tissue prior to sectioning thin samples of tissue. Water is removed from tissue through ascending strengths of alcohol (75% to absolute) and the tissue is cleared in an organic solvent such as xylene. The tissue is then placed in paraffin wax for a number of hours and then set in a mold with wax to cool and solidify; sections are cut then on a microtome.

The Difference between PE Wax and Fisher Tropsch Wax

Fischer Tropsch Wax consists of straight chain that its relative molecular mass is between 500-1000, saturated high alkanes, so it results in this chemical fine crystal structure, high melting point, narrow melting range, low oil content, low penetration, low mobility, low melt viscosity, hard, wear and high stability.

The difference between Fischer Tropsch wax and PE wax:

(1) Molecular weight. Fischer-Tropsch wax molecular weight is much lower than the PE wax. Its branch is also less . It has high crystallinity.It is easy to penetrate into the high viscosity macromolecular chain. Then it can reduce the melt viscosity significantly. Its migration is small in the process.And lubrication effect is obvious in late period.

(2) Fischer-Tropsch wax is saturated straight-linked alkane without double bond. It has strong oxidation resistance and good weather resistance.

(3) Fischer-Tropsch wax viscosity is much lower than PE wax. Its viscosity is only about 10. Less Fischer-Tropsch wax can achieve the same lubrication.Its use is only 70-80% of PE wax.Fischer-Tropsch wax is well compatible with PVC and is qualified for both internal and external lubricants. Fischer-Tropsch wax can be used as good internal lubricants to effectively control the shear conditions, promote flow, control friction and has good melt properties. So, it can improve thermal stability. At the same time, due to its high crystallinity and high linearity of the structure, PVC products can get the best physical and processing performance. During process ,Fischer-Tropsch wax can synthesize alkanes of different chain lengths to change the molecular weight of the final product to form a series of products.

Table 1: Compare Fischer Tropsch Wax  with  PE Wax

Indicator name	Fischer Tropsch Wax	PE Wax
Molecular weight	80-1000	2000-5000
Exterior	Powdery,columnar, granular	Powdery, columnar, flaky
Colour	white	white
Melting range	narrow	width
Melt viscosity (140 ° C)	6-10	20-60
Penetration 0.1 mm	small	high

Hard PVC Formula design

UPVC pipe, also known as rigid PVC pipe, it is amorphous thermoplastic vinyl chloride resin by adding a certain amount of additives (such as stabilizers, lubricants, fillers, modifiers, etc.), and then through the extruder processing into a pipe.

Advantages: light weight, corrosion resistance, high strength, can be recycled and so on.

Disadvantages: high melt viscosity, poor mobility and other processing difficulties.

UPVC hard tube recipe:PVC (SG-5) + stabilizer (lead salt, metal soap) + lubricant + processing aid + pigment

1.PVC  resin

In order to obtain rapid and uniform plasticization, should be used in the suspension of loose resin, resin models are SG-5.

Note: S said PVC resin by the suspension method, G said general-purpose resin, SG-5 for transparent products, hard tube, profiles.

2.PVC stabilizer

Pure PVC resin is extremely sensitive to heat, when the heating temperature reaches 90 ℃ above, it will occur a slight thermal decomposition reaction; when the temperature rose to 120 ℃ after the decomposition reaction intensified; at 150 ℃, 10 minutes, PVC resin from the original The white gradually turns yellow - red - brown - black. PVC resin decomposition process is due to the HCL reaction caused by a series of chain reaction, and finally lead to macromolecular chain breaks. One way to prevent the thermal decomposition of PVC is to add a stabilizer therein to prevent the catalytic degradation of HCl by capturing HCl produced by thermal decomposition of PVC.

Lead salt composite stabilizer has good thermal stability, has been widely used, but the lead salt powder is small, ingredients and mixed, the dust is inhaled lead to lead poisoning, for which the scientific and technical personnel have developed a new Of the composite lead salt heat stabilizer. This combination of additives using a symbiotic reaction technology will be three salt, two salt and metal soap in the reaction system to the initial ecological grain size and a variety of lubricants mixed to ensure that the heat stabilizer in the PVC system in the full dispersion , And because of the co-melting with the lubricant to form particles, but also to avoid the lead dust caused by poisoning. The composite lead salt stabilizer contains the heat stabilizer components and lubricant components required for processing, and is referred to as a fully packaged heat stabilizer.Stable effect is good, transparent, toxic or non-toxic, due to high price limit use.

Rare earth

New varieties, with a transparent, non-toxic and other advantages, great development prospects.

3.Lubricants

PVC melt adhesion metal tendency, between the melt and the friction between the melt and processing equipment, need to add lubricant to overcome the friction resistance. The amount of lubricant added is relatively large. According to the compatibility of lubricants and PVC resin different size, can be divided into internal lubricants (good compatibility) and external lubricant (poor compatibility).

Metal soap (external lubricant)

Metal salts of higher fatty acids (commonly known as metal soap), is one of the commonly used lubricants. In addition to lubrication, but also with PVC heat stabilizer. For a certain kind of metal saponification, the longer the carbon chain of the fatty acid, the better the lubricity. Commonly used calcium stearate, zinc stearate, lead stearate, etc., of which the best stearate lead lubrication

Polyethylene wax (internal lubricant)

PE wax, also known as polymer wax, as a lubricant, its chemical stability, good electrical properties. Compared to other PVC external lubricants, polyethylene wax has a stronger internal lubrication.

4.Fillers

Also known as filler, filler. Add solid materials that improve performance or reduce costs in the material. Organic, inorganic, metallic or non-metallic powders that are normally non-aqueous, neutral, and undesirable with the ingredients of the material can be used as fillers.

Light calcium carbonate (filler)

English: LightCalcium Carbonate, also known as Precipitated Calcium Carbonate (PCC). Is made by chemical processing methods. Because of its settling volume (2.4-2.8 mL / g) than the heavy calcium carbonate sedimentation volume (1.1-1.9 mL / g) produced by mechanical methods, it is called light calcium carbonate.

Features: non-toxic, odorless, non-irritating, usually white.

Calcium carbonate in the plastic products can play a role in the size of plastic products on the stability of the size of a great role, can improve the hardness of the product, but also can improve the product surface gloss and surface smoothness. In the general plastic products to add calcium carbonate heat resistance can be increased, because the calcium carbonate whiteness of more than 90%, can also replace the expensive white pigment to play a certain whitening effect.

5.Modifier (impact modifier)

ACR (Acrylic copolymer) is a core-shell structure of the acrylic copolymer, is a comprehensive performance of the PVC impact modifier.ACR is a combination of impact resistance and processing and modification of the dual function of plastic additives, because of its core / shell structure, so that its PVC products with excellent impact resistance, low temperature toughness, compatibility with PVC, weather resistance, Stability, processing, and the performance and price ratio is moderate, can significantly improve the melt flow of PVC, thermal deformation, and promote plastics, products, smooth and beautiful surface.

2.Chlorinated polyethylene is a high molecular weight polyethylene (HDPE) by chlorination of the reaction of the polymer material. Depending on the structure and use, chlorinated polyethylene can be divided into resin type chlorinated polyethylene (CPE) and elastomer type chlorinated polyethylene (CM) two categories. PVC plastic is excellent anti-impact modifier.

Typical UPVC Formulation (parts by mass)

PVC 100, light calcium 20, lead salt stabilizer 3.5, PE wax 0.3, stearic acid 0.2, processing aid ACR 1.5, paraffin 0.35, titanium dioxide 1.5, group of youth 0.02, brightener 0.02

Extrusion process conditions of PVC hard products

Mix high speed up to 115 degrees, then put the low speed down to 45 degrees, put the material.

Barrel temperature 160 ℃ ~ 180 ℃, head temperature 180 ℃ ~ 200 ℃, screw speed to see models.

Note

PVC ingredients in the formula is very much, to fully mix evenly. Pay attention to the order of feeding, oil absorption of the filler to be added to prevent oil absorption. The lubricant is finally added to prevent the dispersion of the other components. Control the mixing temperature, usually around 115 ℃.

The Type of Lead Salt Stabilizer

Three basic lead sulfate, the formula is: 3PbO · PbSO4 · H2O, code TLS, white powder, density 6.4g / cm3. Three basic lead sulfate is a commonly used stabilizer varieties, generally with the two basic lead phosphite and use, due to non-lubricity and need to be equipped with lubricant. Mainly used for PVC rigid opaque products, the amount is generally 2 to 7 copies.

Two basic lead phosphite, the formula: 2PbO · PbHPO3 · 1 / 2H2O, code DL, white powder, density 6.1g / cm3. The thermal stability of the two basic lead phosphite is slightly lower than that of the three basic lead sulphates, but the weatherability is better than that of the three basic lead sulphates. Dibasic lead phosphite often used with three basic lead sulfate, the amount is generally about three basic lead sulfate lead.

Dibasic lead stearate, code-named DLS, not as three basic lead sulfate, two basic lead phosphite commonly used, with lubrication. Often with three basic lead sulfate, dibasic lead phosphite and the amount of 0.5 to 1.5 copies.

In order to prevent the toxic powder lead salt stabilizer scattering, serious pollution of the production environment, improve the dispersion effect of stabilizers, domestic and foreign has developed a dust-free composite lead salt heat stabilizer. The manufacturing process is:

Under the conditions of heating and mixing will have a synergistic effect of various lead salt stabilizer, auxiliary heat stabilizer and internal and external lubricants and other fully dispersed mixed into granular or flaky lead salt compound stabilizer. It will be added in a certain number of copies of PVC resin (no longer add other stabilizers and lubricants) that can achieve thermal stability and internal and external lubrication of the technical requirements.

There are information on the manufacture of clean lead salt composite stabilizer, the use of lead salt stabilizer particles fine, and thus the surface area with hydrogen chloride increased. And with the internal and external lubricant compound, so that the dispersion of good, heat stability efficiency is significantly improved, the amount can be reduced.

Effects of calcium stearate and stearic acid on the lubrication of paraffin and PE wax

Calcium stearate (CaSt₂) and stearic acid (HSt) in the formula in the presence of paraffin, PE wax conditions can effectively promote the resin plastic and reduce the melt viscosity, so they play from the internal lubrication, are internal lubricants. And in a certain range, the plasticizing time and the plasticizing torque decrease as the CaSt₂ and HSt additions increase.

In the absence of any additives to promote the plasticization of lubricants, only adding delayed plasticized paraffin, PE wax, according to common sense inferred that its plasticization time should be added to promote the plasticization of CaSt ₂ and HSt even longer, but the result is Than any addition to the internal lubricant CaSt ₂ and HSt plasticization time are shorter! It is recognized that the external lubricant mechanism of action: the external lubricant evenly coated outside the PVC particles, so that particles are easy to slide each other, reducing friction and delay the plasticization. But the question is whether it can be completely evenly coated on the PVC particles. Do not use the internal lubricant, only the use of external lubricants can not completely even cover all the RPVC particles, is due to paraffin, PE wax composition of the outer lubricating film tear strength and adhesion strength to the matrix is ​​too small, easy to heat And shear damage caused by. Reason: on the one hand paraffin, PE wax outside the lubricant itself is a non-polar material, between them there is only a small force of the dispersion force (non-polar molecules close to each other, their instantaneous dipole moment will produce very Weak attraction), because the anti-tear strength of the lubricating film is small; on the other hand, the interaction between the polar resin molecules is much greater than that between the non-polar paraffin and the resin (interfacial tension) Together, accumulate in the local part of the resin, and thus can not even wet all the resin particles, so that the role of lubrication.

If there are CaSt₂ and HSt in the system, the polar groups are interconnected with the polar nodes on the surface of the PVC particles, while the non-polar long-chain alkyl moieties are wetted and coated The paraffin liquid film on the surface of the resin particles is miscible (similar to each other), and the wetting layers of adjacent paraffin layers can be thinned and diffused with each other. Polar internal lubricants like "rivets" as paraffin, PE wax wetting film evenly fixed on the metal surface and PVC resin particles on the surface. This "rivet" effect improves the strength of the paraffin, PE wax outside the lubricating film against high shear, maintains the integrity of the lubricating film, thereby delaying the plasticizing time more effectively than using only the external lubricant , And reduced the plasticizing torque.

Therefore, the internal lubricant can not only promote the plasticization, reduce the melt viscosity, and in combination with the external lubricant, and the external lubricant has a better synergistic effect, it can enhance the role of late lubricant lubricant lubrication.

Added: calcium stearate lubrication is stronger than stearic acid.