#polymer engineering

The financial outlook for the Thermoplastic Elastomers Market is characterized by steady, predictable growth. Starting from a volume of 7.40 million tons in 2025, the industry's climb to an estimated 9.23 million tons by 2033 underscores its status as the bedrock of the modern manufacturing sector. This momentum is supported by broad industrial acceptance and a clear, well-defined demand for precision components that continues to expand globally alongside population growth and industrialization.

Navigating Structural Market Shifts

The Thermoplastic Elastomers Market Trends are being redefined by public policy initiatives that prioritize manufacturing self-sufficiency and the expansion of domestic industrial supply chains. Governments are increasingly recognizing the strategic necessity of robust local manufacturing, leading to increased funding for factory modernization and specialized polymer clusters. These systemic investments create a rising tide of demand that benefits material manufacturers, software developers, and engineering firms alike.

Overcoming Industrial Barriers

The industry is working diligently to overcome the historic issues of high capital expenditure requirements and the complexity of regulatory compliance. By emphasizing the integration of digital twin technology and predictive maintenance in polymer compounding, the narrative is shifting from "high-cost production" to "high-reliability manufacturing." This change in perspective is instrumental in driving greater capital engagement and ensuring that facilities remain competitive and profitable in an increasingly crowded global landscape.

Strategic Importance of Collaboration

Polyoxymethylene (POM), commonly known as acetal, is prized for its mechanical strength and dimensional stability. However, when combined with metal inserts, stress cracking becomes a significant concern. This comprehensive guide explores proven methods to prevent this failure mode in your designs. Understanding the Root Causes Stress cracking in POM-metal combinations typically results from…

Understanding POM’s Thermal Limitations Polyoxymethylene (POM), commonly known as acetal or Delrin®, is a high-performance engineering thermoplastic prized for its excellent mechanical properties, dimensional stability, and low friction characteristics. However, when exposed to elevated temperatures, POM faces significant thermal stability challenges that engineers must address. Standard POM…

Abstract

This review is devoted to recent progress in the design of anticancer drug delivery systems with participation of unique polysaccharide gellan gum. At first a brief literature survey on conformational and phase behavior of gellan gum as a function of external stimuli, such as temperature, pH, salt addition etc. is presented. Then the immobilization protocol of anticancer drugs and gold nanoparticles within gellan-based hydrogel matrix is discussed. Release of anticancer drugs from gellan gel matrix to outer solution is considered. Cytotoxicity of gellan gum-immobilized gold nanoparticles together with their anticancer activity is summarized.

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Abstract

Ion exchange membranes (IEMs) are used for exchanging or removing ions from the solutions so that they are fabricated by polymers rather than metals or ceramics. When metal is in contact with the solutions, some reaction or corrosion occurs, and ceramic is difficult to use in membrane form because it is brittle. Also, normal metals and ceramics do not have high ion-exchange properties so that polymers are used widely as a host material of the IEM. The conventional IEMs are either layered membrane consisted of ion exchange material and support layer, and thick bulk membrane. There are no critical problems to use them for water treatment, but they are not suitable for electrochemical application such as reverse electrodialysis (RED). RED is a method of making electricity by sequential ion transport through semi-permeable membranes and electrochemical reaction at the electrode part so that the IEMs need to be developed for getting the structure not to interfere with ion movement through the IEM body. In the RED system, the IEMs are involved in separating ions to create the chemical potential which makes a voltage in the electrochemical system. IEMs for RED has not yet been widely adopted, and most of them are the membrane for electrodialysis (ED). Therefore, we need to study engineering approaches to improve the IEM properties.

Keywords: Ion exchange membrane; Cation exchange membrane; Anion exchange membrane; Polymer; Composite; Structure engineering; Reverse electrodialysis

Introduction

Ion exchange membrane (IEM) is a semi-permeable membrane that consisted of various polymers. When giving the driving force of ion transport, IEM allows the counter-ions and rejects the co-ions [1]. The IEM determines the mobility and selectivity of the ions with assumed that the same driving force is given in the system. There are two types of IEM according to the fixed charge in their body, cation exchange membrane (CEM) and anion exchange membrane (AEM). CEM has a negative charge, thereby the anions are rejected and the cations are exchanged by CEM. On the contrary, since AEM has a positive charge, the cations are rejected and the anions are exchanged by AEM (Figure 1). In addition, IEMs are classified into homogeneous and heterogeneous membranes according to their features. Homogeneous membranes can be fabricated by polymerization of monomers or blending and grafting polymers with different moieties [2-4]. Homogeneous membranes have evenly distributed fixed charges throughout the entire body so that uniform properties appear in all regions. Heterogeneous membranes can be obtained by blending charged resin with a binder and casting them on support [5,6].

Usually, the fixed charge distribution of heterogeneous membrane is uneven compared to homogeneous membrane due to the intrinsic drawback of the manufacturing process. In general, therefore, homogeneous membranes have better ion exchange properties than heterogeneous membranes, but heterogeneous membranes are mechanically strong compared to homogeneous membranes. However, both types of membranes can improve their properties through material or structural engineering. There are many high-quality commercial products in the market (Table 1). In the case of CEMs, the most representative commercial product is the Nafion from DuPont. It has a thickness of 178 nm, IEC of 0.84 meq/g, and exact permselectivity is unknown [7]. NEOSEPTA CM-1 of ASTOM, Selemion CMV of Asahi glass, RALEX CM(H)-PES of MEGA, and CEM type 1 of FUJIFILM are also well-developed CEMs. These products showed a thickness of 100-450 nm, IEC levels of 0.84-2.30 meq/g, and permselectivity of 92.0 -98.8% [5,8]. In the case of AEM, CJMA-2 of Hefei chemjoy, NEOSEPTA AM-1 of ASTOM, Selemion AMV of Asahi glass, RALEX AM(H)-PES of MEGA, and AEM type 1 of FUJIFILM exhibited thickness of 110- 450 nm, IEC values of 0.80-2.20 meq/g, and permselectivity of 90.0-95.0% [5,9-13].

Features of the conventional ion exchange membranes

The conventional IEMs have been developed in an aspect of IEC and mechanical endurance because the conventional products are generally used for adsorbing/exchanging ions to the membrane surfaces in a field of water treatment or ED. These are either layered structure that consisted of ion exchange and support layers or the thick bulk membrane that composed with ion-exchange resin and binder polymer (Figure 2). These type of membranes showed excellent performances for exchanging ions in solution or eliminating specific ions from water, but not suitable to maximize the power density of the applications that ions need to move in an opposite area through the IEM, such as RED. The ions would be hindered physically by a support layer or membrane body in conventional cases, no matter how much other properties are excellent. Thus, the idea that finding a novel material, developing a new surface treatment technique, and conducting structural engineering needs to be considered for fabricating novel IEMs for RED. The RED can be an alternative to overcome the dependency of climate and time for producing electricity because it uses saline water as an energy source. Also, there is no pollutant emission during power generation from the RED system.

The important parameters of the IEM for RED system are the thickness, membrane structure, IEC, areal resistance, and permselectivity, etc. [14-16]. Among them, the thickness and structure of the IEM influence critically the performance of the RED system because it affects how ions move smoothly by penetrating the IEM body. Another thing to consider is the selectivity between cation and anion. If the ion penetrates the IEM easily, the selectivity of IEM is low because it has a trade-off relation between ion conductivity and selectivity. Therefore, it is very important to develop IEMs which has high ion conductivity and selectivity, simultaneously, for expanding the application area of IEMs to electrochemical energy generation.

Operating mechanism and stack configuration of the RED system

The RED system can convert ionic to electric current by circulating two feed solutions that have different salinity, it is just an inverse procedure of the ED system. Salts or solutes in feed solutions are adsorbed to IEM by the induced potential difference between electrodes in the ED process so that the dilute and the concentrate are obtained [14,17]. However, RED makes the ions transport through the IEMs without an applying potential, and current is generated by a redox reaction at the electrode parts. In other words, the concentration difference between the two feeds is the driving force to move the ions, and the alternating CEM and AEM make the ions separate. Thus, high and low salinity solutions need to be supplied alternately across the IEMs for inducing concentration difference. The separation of cation and anion creates a chemical potential in the system so that electrochemical reactions occur to generate electric current (Figure 3) [18-21]. The larger the concentration difference, the higher the power density can be obtained theoretically, but the power density would be decreased owing to an increase of internal resistance in the real case. To enhance the maximum power density, it needs to maintain a high concentration difference between the two feeds with preventing the increase of internal resistance at the same time. IEM is the key to solve this issue. If the IEM performance is improved, the internal resistance of the system would be maintained at a low level even the concentration difference is increased. Therefore, the power density of RED can be determined by the properties of IEM assuming that all conditions of the systems are constant.

Tailor-made ion exchange membranes

Many commercial IEMs are on the market, but they still need to develop for adopting in electrochemical energy generation by overcoming their drawbacks. The methods related to cross-linking (or grafting) other polymers, and incorporating hetero materials on the membrane have been studied. Pal S, et al. [22] evaluated homogeneous phase crosslinked poly(acrylonitrile-co-2-acrylamido-2-methyl-1-propanesulfonic acid) (PAN-co-PAMPS) network CEM with controlling the mol ratio of monomers (AN and AMPS) [22]. By using a PAN-PAMPS-1 membrane including 15 mol% PAMPS, pretty good mechanical ability (tensile strength of 16.4 Mpa) and electrochemical performance (FCD of 0.757 meq/cm3 and transport number of 0.92) were obtained due to its uniform phase mixing of ionic domains and hydrophobic domains. Y. Chen’s group attempted to blend nanoparticles in IEM that were organic-inorganic nanocomposite CEMs such as sulfonated iron (III) oxides (Fe2O3-SO42‒) [23,24] and sulfonated silica (SiO2-SO3H) [25] to improve the IEC, resistance, and permselectivity. The Fe2O3-SO42‒/sPPO nanocomposite CEM was prepared by phase inversion method using the mixture of Fe2O3-SO42‒ particles and sPPO solution. This IEM showed AR of 0.82 Ω cm2, permselectivity of 85.6%, and enhanced gross power density of 1.4 W/m2 [23]. SiO2-SO3H/sPPO nanocomposite CEM was fabricated by phase inversion using the mixture solution. It exhibited AR of 0.85 Ω cm2 and higher gross power density than that of commercial CEM (1.3 W/m2) [25].

Yang S, et al. [26] incorporated ion exchangeable materials into the porous membrane. This is a roll-to-roll (R2R) pore-filling process consisting of pretreatment, impregnation, photo-polymerization, and polishing. The filler material was synthesized by mixing anionic/cationic electrolyte, crosslinking agent, and a photoinitiator. Thus, both CEM and AEM can be fabricated, respectively, depending on which electrolyte is selected and mixed. The pore-filled CEM (PCEM) showed IEC of 1.839 meq/g, AR of 0.475 Ω cm2, and permselectivity of 96%. Also, the pore-filled AEM (PAEM) exhibited IEC of 1.645 meq/g1, AR of 0.661 Ω cm2, and permselectivity of 94.3% [26,27]. Gao H, et al. [9] engineered the surface of AEMs via layer-by-layer (LBL) method with negatively charged poly(styrenesulfonate) (PSS) and positively charged poly(ethyleneimine) (PEI) polyelectrolytes. This membrane has 7.5 bilayers showed excellent anti-organic fouling characteristics and permselectivity. the antifouling potential also increased 30.29% higher than the pristine membrane and the ratio of transport number between Cl- and SO42- was improved from 1.10 (pristine) to 2.44. These results consequently have been enhanced the power density generation of RED by up to 17% [9]. Hong JG, et al. [28] fabricated the hybrid IEMs by the chemical reaction using poly (diallyldimethylammonium chloride) (PDDA) for AEMs and the sulfated polyvinyl alcohol (sPVA) as a hydrophilic polymer with sulfonated poly (2,6-dimethyl-1,4-phenylene oxide) (sPPO) for CEMs to improve AR, permselectivity, and power density [28-30]. R.A. Tufa et al. fabricated a polymer layer consisted of polypyrrole (PPy) and chitosan (CS) to prohibit the passage of the multivalent ions. The modified IEM showed improvement of open circuit voltage (OCV) and power density of 20% and 42%, respectively, compared to the pristine IEM [31].

Conclusion

Since the past, IEMs have been developed with the application of various polymer materials. As a result, high-quality commercial IEMs are being distributed on the market in recent years. These are quite suitable for application in the water treatment field, but their disadvantage is poor ionic conductivity for electrochemical energy applications. Therefore, as the researches introduced briefly in this review, it is necessary to continuously try to apply various materials on IEM, and further studies to suggest a novel structure of the membrane are also needed.

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Abstract

Plastics have advantages and disadvantages in properties like every other material section i.e. wood, metals, aluminum, ceramics. A boon is the high flexibility with plastics to create each desired property for each single application. But this is exactly also the bane. The result are the 5 Billon tons of plastic worldwide everywhere on earth. The diversity of plastic solutions is enormous. This makes reuse of it almost impossible. Compared with no economic value of used plastic the significance for Consumers and companies is almost zero. We need a common strength to solve this problem. And we need true facts from scientists and experts to help consumers make the wright decision under technical, economical, ecological and social aspects. This is shown in detail using a plastic tote bag versus a fiber tote bag.

Keywords: Polymer Engineering; Plastic Products; Advantages and Disadvantages; Boon and Bane of Plastics

Introduction

The “polymer” expertise in interaction with technological knowledge on raw materials, polymer materials, machine and process technology, processing, manufacturing technology and quality, tool and surface technology, construction and simulation, use, repair and recycling, cycles and disposal, Life Cycle Engineering (LCE) and Further training leads to qualified “polymer engineering” and is part of polymer science [1,2]. The specialists working in plastics technology also have enormous competitive advantages and behave sustainably through the application of the engineering concept to innovations in their products and in the quality of their work from a variety of particularly forward-looking aspects (-> economy, component optimization, resource conservation, environmental compatibility, etc.). It should be noted at this point that specialist expertise within plastics technology is basically a reflection of our quality of life and thus our prosperity. This will certainly continue to be the case in future, provided that we are “qualified” and highly responsible when it comes to plastics!

Present situation

From today’s perspective and also in the future, plastics from the following, exemplary selected areas of life will no longer be imaginable.

a. Energy saving through lightweight construction (low density) with moving masses (cars, aircrafts, robots, satellites, rockets)

b. Electrical insulation (including electrical cables, electric motors)

c. Thermal insulation for buildings (foams)

d. Improved shelf life and hygiene of food (packaging)

e. Product protection / resource conservation through shock absorption (packaging)

f. Maximum mobility through rubber tires (traffic)

g. Seat belts in vehicles (shock absorption)

h. Electronic components (mass production)

i. Leisure experiences (skiing, climbing, hiking, ball games, bicycles, water sports, tennis, etc.)

j. Clothing, textiles (comfort, durability)

k. crop yields in agriculture (covers, nets, fences, irrigation, silage)

l. medical healing (bandages, syringes, tubes, plasters, implants etc.)

And for all applications of plastics, these are usually inexpensive.

It should also be noted that due to their extremely high number of variants (materials made to measure for every application), plastics have, besides outstanding advantages (see above) as the boon side, also serious disadvantages (i.e.-> recycling problems) as the bane side.

For about 30 years we have been experiencing how plastics are gradually becoming discredited by public opinion due to “conspicuous” environmental events. These include (selection):

a. Fine dust pollution (microplastics) due to tire abrasion, sports fields with artificial turf,

b. Nanoparticles from cosmetics, fibers from clothing parts lead to plastic in the world’s oceans, in the ground and in the air. Polymer particles (plastic primary particles) migrate through food intake in humans and animals

c. Recycling quotas and circular economy up to ban on disposable products in more and more countries worldwide

d. Consumer health as a result of emissions from packaging and insulation materials as well as floor coverings in the construction industry and much more. Think on PVC soft for example.

e. Reduced moisture absorption of arable soils due to mixed decomposition products made of PE from cover foils etc. over the years.

f. Emissions of additives in plastics (fogging) in new cars, home mobiles, textiles, household machines, departments (floors, furniture), buildings (Inside and outside: foams, surface protections), and so on.

Basically, it has to be demanded that the highest priority must be to generate an accurate factual awareness among consumers through honest, open education. Recognized undesirable developments and misalignments are to be named with clear and understandable names. It is just as important, however, to demonstrate and appreciate the indispensable, environmentally friendly, life-saving, and beautifying consequences of plastic applications.

Plastics are made-to-measure materials, and, from today’s perspective, it is precisely this advantage that is increasingly becoming a major disadvantage with the current possibilities with regard to recycling and reuse (closed loop economy). However, this may change in the future. So “plastic waste”, provided chemical recycling processes (catalytic cracking, etc.) further developed so that in the future the plastic itself will become a source of raw materials again, will receive a completely new appreciation Using solar energy, it is fundamentally possible to achieve a carbon-neutral, climate-friendly life cycle assessment! With glass, metal, ceramics, wood, the situation is similar with regard to a circular economy. Quantitatively smaller, unmixed material flows are significantly larger in number with plastics. With high-strength, alloy steel sheets for car bodies, there is the same problem of pure recycling in the second and subsequent life of a component that is subjected to comparable loads, such as in e.g. PVC window frames. For metals, the need for metals with lower properties is huge worldwide. Similar to thermoplastics, they can be melted and re-alloyed and finally used as normal steel, here, for example, structural steel. With 30-year-old PVC window frame formulations, this is also possible to a limited extent, but the volume flows that can be achieved are much lower at the same time significantly higher logistics costs. Additive developments over the decades also prevent their use after 20 years. a. Without plastics, there would only be mobility based on wood, metal and ceramics (no rubber tires).

b. Without plastics, natural fibers for clothing would not be sufficient for all of humanity or the cultivated areas would be too scarce.

c. Without plastics, we used the oil for heating and transport even faster (plastics reduce resource consumption).

d. Without plastics, there would be no electrical devices, no electrical motors and electronic components

e. Without plastics we would have no surface protection (corrosion)

f. Without plastics, medical technology and hygiene would have been up to 100 years ago.

g. And without plastics there would be no space and aviation technology.

It is also correct, however, that the approximately 9 billion tons of plastics that have been extrapolated since 1950 (2 million t pa) up to 2020 including (approx. 420 million t pa) have a destructive impact on the world’s oceans and that animals and plants suffer from it [3]. This last point is something to be deepened.

The chemical industry produces plastics from (only) 4% of the oil that is extracted annually. 45% each of oil flows into heating + cooling and traffic, another 4% into pharmaceutical products. These usual percentages of mass falsify the picture. Due to the low density of plastics (0.1 g / cm3 for foams up to 2.0 for glass fiber reinforced composites) on average around 1.2 g / cm3), their volumes are much larger. This is the only way to explain that landfills are overflowing, the landscape is polluted, and the oceans are full of discarded plastic products because 15 large rivers (4 of them in Europe) flush tons of waste into the oceans. Although it is people, some unscrupulously criminal, who dispose of plastics carelessly, the manufacturing industry and the legislature - here at the international level-would have been wise to take sustainable countermeasures decades ago. Immediate action and implementation of the measures are imperative here. According to a study by Geyer R, et al. [3], University of California (2017), 6.3 billion tons of plastic were generated by 2015. 600 million tons were processed into recycled materials at short notice and 800 million tons were incinerated. 4.9 billion tons are still in use or accumulate in landfills, in the countryside and in the seas. According to R. Geyer, around 34 billion tons of plastic will be produced until 2050. The plastic flood has to increase.

Life Cycle Engineering

If, on the one hand, the media make a very important contribution to uncovering all kinds of environmental crimes, the same breath is always used for a factual, serious presentation of the relationships waived. An unfounded uncertainty among consumers, often based on general statements, is created. Using the example of , the emotional wrong assessment of the population on the “culprit” plastic can be refuted. Holistic balancing and life cycle engineering are sophisticated methodological tools that are executed correctly and provide good support for decision making. They are misguided when carried out in a biased and incomplete or / and methodically improper manner. For example, the numbers in (Table 1) show that an ftb is more environmentally, technically, and economically disadvantageous than a ptb for some criteria (Figure 1).

The following incident must also be mentioned

In a bill by the German Federal Environment Ministry on November 6, 2019, Minister Svenja Schulze said in the Bundestag: “Plastic bags are the epitome of wasting resources. They are made from crude oil and are often only used for a few minutes. ” Anyone who violates the law can be fined up to € 100,000. Here, as in the example below, the question really arises “Where is the proportionality based on facts and where is common sense?”. The EU prohibits disposable drinking straws of a certain diameter range in 2019. Tecnaro company, Ilfeld, Germany has been supplying the straw market with 100% biopolymers that are quickly biodegradable since 2019. Unfortunately, the latter are no longer allowed because the EU administration apparently forgot to allow biopolymers.

Conclusion

Plastics have material advantages and disadvantages. A tailor-made material can usually be produced based on practical requirements. From today’s perspective, the question of the disposal option is often disadvantageous. If plastic is to be used sensibly and sustainably in our world, it is the task of the specialists (chemists, physicists, engineers, business economists, educators, buyers and sellers) to deal with it professionally and competently from the perspective of society. It does not help the consumer and our earth to be told, that moldable thermoplastic plastics are recyclable economically but only if they are collected separately in plastic groups. The consumer, who has to deal responsibly with the available resources, also hold an outstanding position. However, this requires the truthful information required. As this unfortunately does not take place, as the state of our living environment shows worldwide, it is the task of the experts, together with national and international legislators, to provide prompt solutions to prevent the environmental problem from worsening and to introduce improvements.

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Abstract

In this study, a brief review of the molecular dynamic’s simulations application in research of tribological properties of polymer composites were presented. To better classify and aggregate, particular attention is given to the frictional factor analysis and the enhancement of polymer composites on the tribological properties. The review of the latest research progress of the tribological research by molecular dynamics simulations and some proposals for further research may have implications for the relevant research and applications, which is practically meaningful and helpful for the related researchers to have a better understanding of this field.

Keywords: Molecular Dynamics Simulation; Polymer Composites; Tribological Properties

Introduction

Polymer composites are widely applied in various aspects of scientific and engineering applications, such as industrial production, petrochemicals, automotive industry, military, aeronautics and astronautics, and daily life owing to some of their excellent properties such as wear and corrosion resistance [1,2]. In particular, some important components often face severe working conditions such as high temperature and pressure, corrosion, swelling, and abrasive wear et al. [3,4]. Researchers have done a lot to improve the properties of polymer composites. As is known, simulation has become one of the important methods to study the properties of materials with the development of computer technology. Molecular dynamics simulations have been recognized and widely used due to the unique microscopic perspective as a new simulation method in recent years [5]. As an important index to characterize polymer composites, tribological properties are also one of the key research contents of molecular dynamics simulations. Therefore, many researchers are committed to the research of tribological properties by molecular dynamics simulation.

Discussion

Factor Analysis

The influencing factor analysis of the tribological systems by molecular dynamics methods are first aggregated. Kreer et al. [6] studied the tribological properties of two polymer brushes at different relative sliding speeds. It is found that the lateral force between the polymer brushes decreases logarithmically with an increase in the relative sliding speed v0 in a range that is more than ten times V0. Li et al. [7] developed three-layer molecular frictional pair models between Fe atoms and polymer/carbon nanotube composite to study the friction coefficient and wear rate with different sliding speed of iron nanorods. The results show that the friction coefficient and wear rate of CNT / polymer composites are reduced from 0.356 to 0.322 and 26% -6% at sliding speeds of 0.01 to 0.11 Å / ps. Heo et al. [8] studied the effect of sliding orientation on the tribological properties of polyethylene (PE) by using classical molecular dynamics simulations. The results show that the friction coefficient of sliding in the parallel direction is smaller than that of sliding in the vertical direction. Yuan et al. [9] studied the effect of scratch speed on nano scratching behavior. It was found that when the local temperature in the scratch region exceeds the glass transition temperature Tg, the polymer material in the scratch region around the indenter is removed in a tough manner. Larger scraping rates result in more material deformation and higher pile-up. For larger scraping speeds, the tangential and normal forces are larger, and the coefficient of friction is almost independent of the scraping speeds studied.

Lubrication condition during friction is also one of the focuses of tribology research. Braun et al. [10] used a simple two-dimensional model to study the rolling of spherical lubricant molecules’ effect on the friction system. Molecular dynamics simulations show that the rolling of spherical lubricant molecules exists only when the concentration is lower than that of the closepacked layer. Dai et al. [11] used molecular dynamics simulations to analyze the lubrication effect of perfluoropolyether (PFPE) films to reveal the mechanism behind the interface lubrication behavior of nanoelectromechanical (NEMS) systems and understand the performance of the films. The study found that due to the linear fluidity of the PFPE film, it can promote surface reconstruction and provide good lubricity. The simulation results match the experimental characterization well. Berro et al. [12] used molecular dynamics simulations to study the tribological properties of lubricant mixtures containing cetane base oil and 5% zinc dithiophosphate (ZDDP) under molecular confinement constraints. The results show that mechanical and thermal slip can be reduced by increasing the surface energy. Compared with pure cetane, the migration of ZDDP molecules and their adsorption on solid surfaces can significantly inhibit mechanical slip and leading to an increase in friction coefficient.

Material enhancement

To improve the tribological properties of polymer composites, MD simulations also involve studying from atomic views. Li et al. [13] established and studied a three-layer molecular model that contains Fe atoms as the top and bottom layers and uses the nitrile-butadiene rubber and carbon nanotube matrix as the core to understanding how to improve nitrile-butadiene rubber composition by incorporating carbon nanotubes as a reinforcing agent. Chawla [14] Developed graphene-reinforced natural rubber composites to study the improvement of mechanical and tribological properties of natural rubber by introducing graphene as a reinforcing material. The results show that after strengthening natural rubber with a single-layer graphene oxide sheet, Young’s modulus increased by 185%, the shear modulus increased by 32%, and the hardness increased by 48%. Moreover, the friction coefficient and wear rate obtained by introducing graphene oxide sheets in the natural rubber matrix were reduced by 28% and 36%. He et al. [15] used molecular dynamics simulations to study the enhanced tribological properties of polymer / nano- SiO2 composites by sliding a top iron layer on the surface of the polymer composite. The results show that by introducing nano- SiO2 particles, Young’s modulus is increased by about 190%. The average friction coefficient and wear rate of the polymer / nano- SiO2 composites were reduced by approximately 27% and 47.4%, respectively. Li et al. [16] established a molecular model with Fe atoms as the top nanorods and the bottom layer and a polymer/ carbon nanotube composite as the core to check the friction by sliding the top Fe nanorods on the surface of a polymer matrix under normal load coefficient and wear rate. Simulation results show that by introducing carbon nanotubes, the average friction coefficient of the composite material is reduced by about 38%, and the average wear rate is reduced by 60%. Chawla et al. [17] used molecular dynamics simulations to study Young’s modulus and tribological properties of pure styrene-butadiene rubber (SBR) polymers and carbon nanotube-reinforced polymer composites. The mechanism of using CNTs to enhance friction performance was studied and discussed. When carbon nanotubes are used as the reinforcing material, the obtained Young’s modulus indicates that the mechanical properties of the SBR polymer are improved.

Conclusion

Molecular dynamics has been widely used in the study of tribological properties of polymer composites for its excellent advantages. However, due to the large amount of calculation and the small calculation scale, the limitations of large calculation time, fluctuation in results and the susceptibility to size effects cannot be ignored. In the foreseeable future, the research on the mesoscopic scale, the improvement of atomic-scale research methods and the combination with macro-scale simulation methods will be some areas worth further exploration for the molecular dynamics study of the polymer composites on the tribological and some other properties. The contribution of this study is expected to broaden the research area of molecular dynamics and conduct a more thorough and comprehensive study of rubber materials.

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Abstract

Cationic polymerization of p-methyl styrene by phenacyl triphenyl phosphonium, phenacyl triphenyl arsonium and p, p`-bis[(triphenylphosphonio) methyl benzophenone salts [1-3], and cation radical salt of p-substituted triphenylamine having different p-substilments was carried out photochemically and/or thermally. Cation radical amine salts were found to be more effective thermally in comparison to phosphonium or arsonium salts. The effects of initiator structure, counter ion, concentrations of salts and reaction conditions on the rate of polymerization in dichloromethane on the isolated polymer will be presented Figure 1-3.

Keywords: Phenacyl triphenylphosphonium salts; Phenacyl triphenylparsonium salts; tri p-substituted triphenyl amine salts; p-methyl styrene; photo polymarization; thermal polymarization

Introduction

Poly (p-methyl styrene), PMS has excellent potential for a broad range of applications in industrial products, for example, reinforced plastic composites achieve higher thermal stability when PMS substituted for styrene [1]. The reactivity of para-substituted styrene towards cationic polymerization depends on the type of substituent with the following order; OCH3> CH3 > H > Cl have been established. Phase transfer catalyzed chlorination of poly (p-methyl styrene) occurs by the action of commercial aqueous sodium hypochlorite solution to produce the chloromethylated polystyrene, which is a key intermediate in the preparation of anion exchange resins [2], and for lithographic evaluation [3-5].

phosphonium salts such as p, p`-bis [(triphenylphosphonio)methyl] benzophenone are reported to be useful photoinitiators for the cationic polymerization of epoxide and vinyl monomers [6]. Recently, we reported on the use of phenacyltriphenyl phosphonium and arsonium salts as photoinitiators for the cationic polymerization of cyclohexene oxide [7], and styrene [8] and p-methylstyrene [9].

This paper will further examine the photoinitiated polymerization of p-methyl styrene by onium salts [1-3] and thermally by cation radical salts [4-6] at room temperature, and in dichloromethane.

Experimental Procedures

Onium salts preparations and characterizations were performed as reported previously [7]. The bromide salts were converted to the required photo initiator by adding 0.1 mole of each salt in 150mL of water to a mole of the KPF6 or KPF6 dissolved in 50mL of water. Para-methyl styrene, and dichloromethane (Fluka) were dried over calcium hydride and distilled prior to their use. Acetone (Fluka) “AnalaR” grade was used as received.

Spectroscopic measurements

Ultraviolet spectra were obtained on a Cary-2300 spectrophotometer. Infrared spectra were recorded on a Nicolet 50xB FT-IR spectrophotometer. NMR spectra were taken in CDCl3, on a XL- 200 pulsed Fourier transform NMR spectrometer with tetramethyl silane as the internal standard.

Photopolymerization by onium salts (1-3)

Photoinitiated polymerization was carried out in a 15mm diameter Pyrex tube using a tight syringe for monomer addition. A homogeneous solution was formed. The reaction tubes were then closed with rubber septum, and irradiation was carried out using a merry-go-round photo reactor, Model RPR 100, obtained From the Southern New England Company. Inside the reactor’s barrel was a “merry-go-round” holder, which rotate continuously by a motor, and was surrounded by sixteen Honovia 450 watt, medium pressure mercury lamps placed at a distance of 5cm from the sample. The samples were placed in the holder, and were irradiated for the required period, using a light source of 350 nm wavelength. Poly (p-methylstyrene) was precipitated by addition of methanol, filtered, dried and weighed. From the polymer masses, the rate of polymerization was determined gravimetrically. The polymerization of p-methylstyrene by salts (1-3) is shown in Figure 4.

Thermal polymerization by cation radical salts (4-6)

Tris-p-substituted triphenylamines were fairly readily oxidized to form stable cation- radicals, and polymerization of cationically susceptible epoxide and vinyl monomers have been carried out by stable soluble, tris-(p-Bromotriphenyl) amine cation radical salts having stable counter anion such as SbF6 - [10,11], which are prepared as shown in Figure 3.

Solution of the isolated salts [4-6] was found to be stable in dichloromethane, for a period of several days under laboratory conditions. The relative stability of these salt solutions in dichloromethane and under normal laboratory conditions can be arranged as follows: salt 4 > salt 5 > salt 6 Figure 6.

Polymerization procedure

Selected amounts of monomer and initiator solution, in dichloromethane were placed into a Pyrex tube closed with rubber septum and flushed with nitrogen. The tube was placed on a holder and left immersed for the required period in a water bath held at 25oC. Rapid addition of initiator was achieved by syringe injection. The polymer was precipitated into methanol, filtered, dried, and weighed. Polymer yield percentage and rate of polymerization were determined gravimetrically [9]. The number averaged molecular weight (Mn) of the isolated polymer was measured in toluene on a “Hewlett Packard” (Model 501), and High-Speed Membrane Osmometer in toluene. Molecular weight distributions were determined using a “Waters Associates” (Model 200) GPC, fitted with differential refractometer detector. The system was examined at 25oC in THF with a solvent flow rate of 1.0mL/min and a polymer concentration of 1.0mg/mL. Molecular weights were calculated with reference to polystyrene standards.

Results And Discussion

For polymerization by onium salt (3) PMS obtained after 30minutes, the weight average molecular weight, MW was found to be 111, 287g per mole, and the number average 41, 680 g per mol, Mw/Mn = 2.67. In the case of phenacyltriphenyl phosphoniu and Arsonium salts, Bronsted acid is most likely to be the initiating species. Upon photolysis of these salts, the resonance stalilized ylide and protons are formed according to Figure 5. The suggested mechanism by which photopolymerization of p-methylstyrene initiated by the use of onium salts is given in figure below.

Figure 6 compares the efficiency of cation radical salts [4-6], under the same conditions. The reaction mixture contained 2.53M monomer and 3.3 x 10-4M in dichloromethane. The results in Figure 6 show that the efficiency of cation- radical salts (4-6) fall in the following sequences: salt 6 > salt 5 > salt 4. Photolysis of reaction solution containing the monomer and these cation radical salts in the concentration range reported, changed the reaction mixture color from blue to orange/red upon photolysis of salt 5 and salt 6, and low polymerization, while solution of salt 4 showed significant increase in the amount of polymer obtained. These results suggested that photolysis of salt 5 and 6 leads to splitting of the Br anion, which terminated the propagated chains at the early stages of the reaction. Interaction of the cation radical salt with the monomer is the key step in the polymerization process, as polymer chains would grow following thermal initiation by both the protonic acid (H+) produced and the amine ended carbonium ion. Glass transition temperature of PMS obtained by salt (6) after 6 minutes was 381.750K, the weight average for the same sample was 68,766g/mole, the number average was 27, 022g/mol, and the Mw/Mn = 2.54.

Conclusion

Triphenyl phosphonium, arsonium and cation radical salts were found to be effective thermal initiators for the cationic polymerization of p-methyl styrene. The polymerization was initiated thermally when the cation radical salts were utilized, and photochemically when phosphonium and arsonium salts were used.

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