Plastic materials: chlorinated polyethylene (CPE), chlorinated polyvinylchloride (CPVC), chlorosulfonated polyethylene (CSPE) and polychloroprene rubber (CR)
Abstract:
There are a number of plastic materials used in the construction industry that are known either to emit volatiles to indoor air or to leach organotins, both of which can affect comfort, health and productivity. Emissions or leaching can depend on the composition of the plastic material involved along with the various parameters associated with it. Within these plastics, there are chlorinated and chlorosulfonated polyethylene, chlorinated polyvinylchloride, and polychloroprene rubber, all which are the main subjects of interest for this chapter. Their properties, uses and health effects are briefly presented and some alternative materials for their use are presented.
3.1 Introduction
A range of various plastic materials are used in buildings for different purposes and for different applications, in a number of mechanical, electrical and plumbing (MEP) systems, due to their properties and the economy provided. However, there is also an ever growing concern about the potential health effects of these plastic products, composites and various chemicals that are being used in buildings. Some of these can emit volatile organic compounds (VOCs) into the indoor air, changing the indoor air quality (IAQ), that can affect human comfort, health and productivity. These VOCs depend on the type of plastic involved along with the various parameters associated with it (i.e., purity and the type of additives used during preparation, if not pure), as well as parameters like the temperature and relative humidity during their application, and even the circulation of the air above their surfaces. Effects of VOC can vary from irritation of mucous membranes to the introduction of a number of respiratory diseases and several adverse health effects, as well as to endocrine hormone disruption in humans (EDC). In a number of cases, it is shown that VOCs can even trigger cancer. In addition, various studies showed that there can be a number of harmful organic contaminants in house dust, such as different polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), etc., some of which were commonly used until quite recently in electrical insulators.
A number of toxic heavy metals and compounds (e.g. lead, cadmium, chromium, mercury, bromine, tin, antimony, etc.) are used in additives (e.g., pigments, fillers, UV stabilizers, and flame retardants) for plastics. These compounds, although encapsulated in the polymer matrix in suspension form, are chemically unbound to polymer molecules and can be gradually released into the contacting environment over the service life of the plastic object, which can create serious health and environmental problems, as most of these elements are identified as toxic to humans. There are a number of examples that can be given for the leaching of these additives into the contacting medium from the plastic matrix. Most of these migrations can be direct, but they depend on time, temperature and characteristics of the environment at all times. Probably the most direct example is plastic water pipes prepared with organotin stabilizers as additives, from which toxic organotin compounds are shown to leach to the water, which can be most critical if drinking water is involved (Forsyth and Jay, 1997). These migrations are shown to be even accelerated by the existence of chlorine dioxide in the water, leading to the rather quick deterioration of pipe material in the end (Fig. 3.1) (Hassinen et al., 2004; Yu et al., 2011; Whelton and Dietrich, 2009; Devilliers et al., 2011; Ojeda et al., 2011; Azhdar et al., 2009; Skjevrak et al., 2005; Hoang and Lowe, 2008).
Fig. 3.1 Scanning electron micrograph of a specimen obtained by sectioning through a region with a crack in a pipe exposed to water containing 4 ppm chlorine dioxide for 121 h. (reprinted from the paper by Yu et al. in Polymer Degradation and Stability, 96(5), 790–797, 2011. Kind permission of Elsevier UK is acknowledged)
Similarly, when disposing of these plastic wastes, either by incineration or by placing in landfill, toxic metal compounds can be released from plastics entering the atmosphere or leaching into the soil.
Within the various additives mentioned, there are also plasticizers which are in general organic esters of a low volatile nature, which can migrate directly as a result of leaching. Most of the plasticizers are carcinogenic. One common example is DEHP (di-ethylhexyl phthalate), a phthalate plasticizer largely used in PVC, for which replacement with its non-toxic alternatives is suggested.
In addition to the application of plastic materials in construction (and in all other applications of our everyday life) where plastics are in the processed form, and interest is mostly in health issues connected with their use, the possible health effects on the environment at the production stages have also drawn some criticism from time to time. In this connection, one should remember the Bhopal disaster in India, some 25 years ago, in which more than 40 tons of extremely toxic methyl isocyanate gas (used in pesticides and for production of polyurethane rubber) escaped from a plant in Bhopal and killed over 5000 people within days; according to local authorities, nearly 10,000 more people have subsequently died of complications from cyanide lesions (Bagla, 2010).
Concerning health effects on the environment, another well-known example is the effect of chlorofluorocarbons (CFCs) on the ozone layer. CFCs were used until recently by plastics processors as foaming agents for the production of polystyrene and polyurethane foams. Although they are non-toxic directly, they have indirect health effects because of their effect on ozone depletion, as well as global warming. CFCs and other halogenated ozone-depleting substances (ODS), like carbon tetrachloride and trichloroethane (in short, the haloalkanes), are mainly responsible for the increased UV radiation as the result of ozone depletion, which has a number of biological effects like skin cancer, cataracts, etc. (McFarland and Kaye, 1992). The Montreal protocol (2007), recognized by the UN, phases out the production and use of ODS, including CFCs, while encouraging the search for their ozone-friendly alternatives (UNEP, 2006).
Among the most commonly used plastics in buildings, there are polyethylene (PE) and polyvinylchloride (PVC) and several of their derivatives, such as chlorinated polyethylene (CPE), chlorosulfonated polyethylene (CSPE), chlorinated polyvinylchloride (CPVC), and polychloroprene rubber (or neoprene, CR), all of which, with their probable effects on human health, will be the main subject of our interest for this chapter.
In green building certifications, plastic materials like CPE, CSPE, PVC, CPVC and CR are in general considered among the most challenging group of materials to take into account (in general, they are sometimes even termed ‘red-listed materials’).
3.2 Structure and properties of chlorinated polyethylene (CPE), chlorinated polyvinylchloride (CPVC), chlorosulfonated polyethylene (CSPE) and polychloroprene rubber (CR)
All of these materials are prepared by proper modification of the related base plastic material (PE and PVC, respectively), which involves a chlorination process for all, and additional sulfonation in the case of CSPE, yielding new systems with certain improved desired properties. CR is the product of a chlorine-containing monomer, chloroprene.
3.2.1 CPE and CSPE
CPE and CSPE are produced by chlorination (and additional sulfonation for the latter) of PE (polyethylene, also called polythene, or poly(1-chloroethylene) according to IUPAC), which is a low-cost general-purpose thermoplastic material. PE was initially introduced as a dielectric material specifically for high-frequency insulation, and later used also for piping (domestic and agricultural water piping, as well as gas piping) and extensively in cable and other wire-covering applications.
A number of different grades of PEs are involved, each giving rise to different CPE/CSPE products with different properties after chlorination; hence, it may be necessary first to give a brief summary of the different PEs available. Depending on the technique used in its production, it is possible to obtain many kinds of PE differing in density, percent crystallinity, molecular weight, molecular weight distribution and branches, such as (a) low-density LDPE, a highly branched, high-pressure grade of PE; (b) high-density HDPE, a linear, low-pressure grade; (c) linear low-density grade, LLDPE, etc.
Different grades of PEs were, and still are to some extent, used in the building industry with some inherent drawbacks. PEs in their pure state are free from odor and toxicity. However, they also have low softening temperatures, their low molecular weight grades are easily susceptible to environmental stress cracking (ESC) and easy oxidation, they can easily develop opacity in bulk, they have poor scratch resistance, and they lack rigidity with rather low tensile strengths and high gas permeabilities, all of which are their main limitations in use, that need improvement (Brydson, 1982). However, they are still used to some extent because they are economic and easily processable, they offer excellent electrical insulation and chemical resistance/reactivity properties, and their toughness and flexibility can be retained even at low temperatures.
The reactions that occur during chemical modification of PEs are rather unique and different, firstly due to the chemical inertness of the molecule, and secondly due to the existence of crystalline and amorphous regions in the structure. The crystalline region is the part that is less readily attacked by any chemical (i.e., chlorine) as compared to amorphous parts, due to the difficulty of diffusion of any reactant into the crystalline areas. To overcome this difficulty, usually a pre-modification is performed in a good solvent with the aim of destroying any crystalline regions.
CPE (CAS number: 64754-90-1)
Chemical modification of PE can be accomplished in a number of different ways. Chlorination of PE is a simple halogen substitution reaction (Jones, 1964), which usually alters both the regularity of the chains and softening points significantly, with properties of products varying with degree of substitution as well as conditions of chlorination (Fettes, 1965). Chlorination can be done in bulk (fluidized bed), as emulsion or suspension in an inert medium or in solution (i.e., CCl4), the first of which results in more crystalline products at comparable levels of chlorination. When carried out in solution, the chlorination is random, but when carried out with the polymer in the form of a slurry, the chlorination is uneven and is due to residual crystalline zones of CPE, the material remaining as a thermoplastic (Akovali and Vatansever, 1983, 1986; Chlorinated Polyethylene, 2011).
Chlorination in general increases interchain attraction; and, once there is sufficient bound chlorine to give rise to a completely amorphous product, chlorination can cause an increase in softening points. In fact, CPEs are usually rubbery in the 25–40% range, depending on the type of PE used (HDPE or LDPE, respectively); and at about 45%, the polymer becomes stiff at ambient temperatures. With a further increase in the percentage of chlorine, the polymer becomes brittle. Chlorination in all cases results in a considerable decrease in flammability, whereas solubility may be increased or decreased depending on the chlorine content.
CPE thermoplastic rubbers are commercially available and were first patented by ICI in 1938. They have several attractive physical, mechanical and chemical properties, such as very good chemical, oil, heat, flame, ozone and weathering resistances, good low-temperature performance, compression-set resistance, flame retardancy, high filler acceptance, tensile strength and resistance to abrasion, with competitive prices; and they are also available in powder form. In addition, they can range from crystalline (or rigid) thermoplastics to flexible elastomeric products, which makes them highly versatile. However, because of the difficulties involved in their processing and particularly their vulcanization (crosslinking is done only by using peroxides), so far they have never been able to achieve much market value and commercial significance, and the market is already mostly taken up by CSPE.
Thermoplastic CPEs are seldom used on their own but primarily in blends with other polymers, mainly for white and brown profiles of PVC as impact modifiers. If chlorination is carried to a level at which the polymer is only semi-compatible with PVC, a blend with high impact strength may be obtained and the material is classified as an impact modifier (Feldman, 1989), and also as a modifier for PE, ABS, SAN and PP. CPE is used extensively, alone or in blends with acrylic impact modifiers, to achieve a desirable combination of ductile impact and processing performances. CPE is also used to improve the resistance to ignition and combustion of PVC systems. CPE finds uses in pipe applications, typically in specialty PVC pipe, CPVC pipe, electrical conduit, and any highly filled compounds in this category. Other important end-use applications of CPE include wire and cable jacketing, roofing membranes, geo-membranes, hose and tubing, coated fabrics, molded shapes, extruded profiles, damp-proofing under concrete floor slabs or to produce synthetic building wraps, and gaskets. CPE is the modifier of choice for cost/performance efficiency in vinyl siding substrate, providing toughness at low temperatures, ductility, and a high capability for filler acceptance. It provides excellent impact properties, filler acceptance, and ductility in vinyl fence substrates, and can also be utilized in capstock applications. All of these applications already exist in the construction industry.
China currently is the world leader in CPE production (83%), while China and the US were, and still are, the two largest consumers of CPE in 2008, (Ormonde and Klin, 2009). Specifically, in China, roughly 75-80% of CPE is used for impact modification of PVC for door/window profiles and pipe/drainage applications, and of certain styrenic copolymers, followed by 20-25% in flexible sheeting for various roofing applications, electrical wires and cables, and others (e.g., hoses and seals). In the US, 80-90% of CPE is consumed for impact modification and the rest is for other uses (wire and cable jacketing, roofing, hose/tubing and molded articles).
Some characteristic mechanical/physical properties of CPE are presented in Table 3.1.
Table 3.1
Some characteristic properties of CPE
| Density | 1.16 g/cm3 |
| Chlorine content | 25–42% by weight (can be maximum 70%) |
| Hardness (Shore) | A 60 |
| Tensile strength | 12.5 MPa |
| Flexural modulus | 0.02 GPa |
| Elongation at break | 700% |
| Stable time at 165 °C | 8 minutes |
| Max. operating temperature | 60 °C |
| LOI (Limiting Oxygen Index) | 22 |
The health effects of CPEs may be listed as follows.
CPEs can be formulated to be hard or flexible without the need to use plasticizers, and special additives can be employed otherwise (as UV and heat stabilizers, antioxidants, etc.) to provide additional required properties. In such cases, these additives will be a serious concern for any possible emission of VOCs at ambient and elevated temperatures and they should be selected carefully.
This can occur in a CPE processing facility, where good housekeeping and dust control are necessary for safe handling. Dust particles of CPE may cause eye discomfort (hence chemical goggles are needed), and skin contact should be avoided.
Thermal degradation (thermal decomposition and combustion, although CPE combusts with difficulty) of CPE can produce mainly HCl (hydrochloric acid) and CO (carbon monoxide), which are highly irritant and toxic, in addition to dioxin or dioxin-like products, which are highly toxic and carcinogenic. In fact, if only the base polymer (PE) is considered, its thermal degradation produces mainly CO (carbon monoxide), which is considered as a systemic toxin (Ammala et al., 2011).
CSPE (CAS number: 9002-88-4)
Chlorosulfonated polyethylene (CSPE or CSM rubber) is a synthetic rubber based on PE that is noted for its resistance to chemicals, to temperature extremes (i.e., suitable for continuous use up to about 130 °C, and for intermittent use even up to some 30 °C higher), and to aging and ultraviolet (UV) light. CSPE is patented by DuPont (DuPont Performance Elastomers, a subsidiary of DuPont), with the trade name of Hypalon (Tornqvist, 1986).
CSPE/CSM rubber is used in a variety of industrial and construction applications that require high performance. The driving force behind CSPE consumption in the world is the automotive sector. Nearly one-fourth of total world consumption of CSPE was in the automotive industries in 2008. The second-largest market for CSPE is in construction applications in roofing membranes and liners for ponds and reservoirs. They are widely and specifically preferred and used in roofing. In fact, within the commercial roofing market, CSPE has the biggest share, followed by PVC and ethylene–propylene–diene monomer terpolymer (EPDM) (Griffin, 1982).
In addition to in (single-ply) roofing and geomembrane applications, CSPE/CSM rubbers are used in geosynthetic applications as liners, caps and floating covers as well as to make inflatable boats, gaskets, weather stripping, wire and cable insulation.
The first production of CSPE on a laboratory scale was achieved by McQueen (1939), who treated a suspension of LDPE (a newly discovered material at that time) in CCl4 with SO2 and chlorine, with the hope of producing a new water-soluble polymer containing sulfonic acid groups; this resulted in the introduction of both chlorine and sulfonyl chloride groups (SO2Cl) by replacing some of the H atoms through elimination of HCl on the polymer backbone. The sulfochlorination of PE can be carried out either on the solid material or in solution. In sulfochlorination in solution, chlorine and sulfur dioxide are allowed to react, in the presence of UV or azo initiators, with PE dissolved in hot CCl4 (equation 3.1):
Several years later, McAlevy and coworkers (McAlevy et al., 1946; McAlevy, 1947) realized that sulfochlorinated PE of the right composition exhibited outstanding properties in a number of applications, mainly because of its good heat resistance and exceptional resistance towards aging, in general. For the PEs available at the time (1947), the optimum elastomeric properties were found to occur at chlorine contents between 27 and 30%. McAlevy and colleagues recognized that chlorine substituents were particularly important to the elastomeric properties (the chlorine atoms break up the regularity of the PE chain structure with decrease in crystallization, thus imparting an elastomeric character to the polymer), while the sulfonyl chloride groups made the polymers curable with metal oxides (MtO) and water (i.e., either MgO, ZnO or PbO and a hydrogenated wood resin as the source of water). Crosslinking through sulfonyl chloride to give OMtO crosslinks (with MtCl2 elimination) is found to lead to an elastomer of commercial interest, i.e., a typical final amorphous CSPE product with 27 wt% chlorine and 1.2% sulfur can be made with a glass transition temperature (Tg) value of − 55 °C (Morton, 1959).
Based on these developments, DuPont started small-scale production of CSPE under the name Hypalon in 1954, followed by a full-scale commercial plant (Ziegler et al., 1955). By that time, new types of PEs had become available through Ziegler/Muelheim catalysts (equation 3.2), such that Heuse (1958) tried to make ‘higher density-more linear’ PEs available successfully. He demonstrated that chlorine levels in the range of 38–48% could be advantageously used. When cured, these polymers exhibited additional outstanding resistance towards swelling (by oils and organic solvents). Fillers are not needed for optimum strength. Most grades of Hypalon today are based on the latter type of PE. In a typical commercial polymer, there is one 1-2-chlorosulfonyl group for each 200 backbone carbon atoms, namely, 25–42% CH2CHCl and 1-2-(− CH2CH(SO2Cl)−) groups per ethylene group.
Some typical mechanical/physical properties of CSPE are presented in Table 3.2.
Table 3.2
Some characteristic properties of CSPE
| Tensile strength at break | 18 Pa |
| Elongation at break | 200% |
| Hardness (Shore) | 90 |
| Continuous service temp. | − 50 °C (lower) to 200 °C (upper) |
| Tear resistance | Good |
| Adhesion | Excellent |
| Weather/ozone resistance | Excellent (better than neoprene and butyl rubber) |
| Oil resistance | Good |
| Water swelling resistance | Excellent |
| Adhesion to metals | Excellent |
CSPE in general is poor in ‘snap’ and ‘rebound’ characteristics and some grades may have a small ‘permanent set’. Its abrasion resistance, flex life, low-temperature brittleness and resistance to crack growth are all good. CSPE is flame resistant. It is superior to polychloroprene (neoprene) in overall properties, and inferior to, but more cost-effective than, silicone or fluoro-elastomers. Compared with CPE, CSPE elastomers exhibit much better mechanical properties and abrasion resistance.
DuPont is still the dominant producer of CSPE, with some Japanese and Chinese competition.
CSPEs are considered as safe materials, in general. Possible (acute or chronic) potential health effects of processed CSPE materials arise mainly from the possible evolution of CCl4 (Dupont MSDS, 2008). The route of entry of this chemical into the body is either through the skin or by breathing, which may cause skin, eye, nose, throat, and/or lung irritation; the ultimate target organ is the liver and central nervous system as well as the kidneys.
In addition, if any sort of additives are employed in CSPE formulations to provide additional required properties, then these additives may be of serious concern for any possible emission of VOCs at ambient and elevated temperatures, and they should be selected and followed carefully. Thermal degradation (thermal decomposition and combustion, although CSPE combusts with difficulty) can produce mainly HCl, SO2 and CO, which are highly irritant and toxic, in addition to possible dioxin or dioxin-like products, which are toxic and carcinogenic.
The carcinogenicity of CSPE is not known specifically. It is an IARC 2B (IARC stands for the International Agency for Research on Cancer) and ACGIH A2 (ACGIH stands for the American Conference of Governmental Industrial Hygienists) classified material, meaning it is a possible (suspected) carcinogenic substance for humans, where there is limited evidence of its carcinogenicity in humans and no (or inadequate) supporting evidence in experimental animals (Akovali, 2007).
3.2.2 CPVC (CAS number: 68648-82-8)
CPVC (chlorinated PVC, ‘post-chlorinated PVC’, or polychloroethene) is another modified polymer which is widely used in the construction industry. It is produced by subjecting PVC resin to a post-chlorination reaction (mainly to increase its Tg), which, with a free radical reaction, results in the addition of chlorine atoms on the base PVC molecule backbone to replace H, typically initiated thermally (or by UV) (equation 3.2):
CPVC can be made by any commercial chlorination process, such as by solution, fluidized bed, water slurry, thermal, or liquid chlorine (Noveon, 2003). Some of these methods have been associated with the use of swelling solvents. Depending on the variations on the methods employed, CPVC products with different chlorine contents can be obtained (ranging from 56.7% for the base for PVC to 74% by mass, but for most commercial resins 63-69%); at 70% mass of chlorine, CPVC becomes unstable.
CPVC is an amorphous thermoplastic material similar to PVC, with the following added advantages:
• Higher heat distortion temperature (operating temperature range is between 0–90 °C as opposed to 0–60 °C for PVC)
• Improved fire performance properties (with limiting oxygen index value of LOI = 60, CPVC does not support combustion).
In addition, CPVC keeps the same advantageous properties as for PVC, as follows:
• It has excellent environmental resistance to aggressive caustic and acidic fluids (but not to most solutions of acids, alkalis, solvents, aromatics, and some chlorinated hydrocarbons).
• It has good abrasion and long-term strength resistance with high stiffness values.
Some typical mechanical/physical properties of CPVC are given in Table 3.3.
Table 3.3
Some characteristic properties of CPVC
| Density | 1.56 g/cm3 |
| Young’s modulus (E) | 2.9–3.4 GPa |
| Tensile strength | 50–80 MPa |
| Elongation at break | 20–40% |
| Notch test | 2.5 kJ/m2 |
| Glass transition temperature (Tg) | 106–115 °C |
| Operating temperatures | 0 °C (lower) to 90 °C (higher) |
| Resistance to acids, caustic substances, organic and inorganic solvents (except strong oxidizing acids) | Good |
CPVCs offer an economic solution for a wide diversity of both pressurized and non-pressurized corrosion-resistant hot and cold water plastic piping systems in use as plumbing materials, at both normal and elevated service temperatures, mainly due to their long-term strength characteristics, high stiffness and cost-effectiveness in domestic and industrial applications. In pressurized systems, they can be used with fluids up to 80 °C. CPVC pipes are categorized by two criteria: basic short-term properties (including mechanical strength, heat resistance, flammability, and chemical resistance) and long-term hydrostatic strength. CPVC pipe, tube, and fittings have been successfully used worldwide in hot and cold water distribution systems in the construction sector since 1960. Usage of CPVC pipes and fittings in gas, sewage and water piping applications has tripled in the EU in recent years, and they are overwhelmingly used in construction as a main competitor to metallics. Bacteria build-up with CPVC is much lower than with alternate piping materials, including metallic materials (copper and steel) and other thermoplastics.
CPVC is a preferred material for the production of fire sprinklers, and CPVC applications as inner corrosion liners in (water) tanks and vessels are very common. Chlorinated paraffins, mainly CPVC, are also widely used in PVC for adhesive applications, in sealants (mostly polysulfide polymer-based ones) as plasticizers, and in PVC for wire and cable coats.
The main producer of CPVC is Noveon Corporation (successor to B.F. Goodrich, USA), followed by both Taiwan and China.
As regards the health concerns for the use of CPVC, no significant specific health hazard has been reported for its use at ambient temperatures, although there exist several possible expected effects of this material under different conditions, as follows.
Firstly, as in the case of PVC, mechanical properties of CPVC can be modified further at large by using conventional compounding techniques, and CPVC pipe and fittings can have a number of different chemical constituents. The resin itself has certain strengths, i.e., combination of high temperature and high corrosive resistances, mechanical strength and excellent lifecycle economics, as well as weaknesses, such as low impact resistance, susceptibility to oxidation and thermal degradation at higher (extrusion) temperatures. Hence, first of all, suitable impact modifiers are needed, i.e. high rubber butadiene content, and high-efficiency methylmethacrylate–butadiene–styrene (MBS) and acrylonitrile-butadiene-styrene (ABS) impact modifiers are used at about 3 to 15 p.h.r., which are not expected to cause any health effects.
In addition, other additives are employed (Noveon, 2003). CPVC compounds are approximately 85% CPVC resin and 15% additives, such as antioxidants, lubricants, stabilizers, tinting colorants, pigments, Tg enhancing additives and processing aids. Each of these additives can pose a health hazard depending on their structure, concentration and conditions. As an example, if heat stabilizers are considered, suitable heat-stabilizing ingredients mostly include phosphate stabilizers (such as disodium phosphate), maleimides, sulfur compounds and alkyltin compounds. Until recently, the latter was preferred specifically for CPVC piping systems.
Various organotin compounds (mostly mono- and disubstituted alkyltins) are the most widely used heat stabilizers (organotin compounds are used at 2–4% in CPVC pipes) in the manufacture of PVC and CPVC plastics, including water pipes, which may leach into water easily when they come into contact with drinking water (Boettner et al., 1982). Although still at low concentrations, a dibutyltin sulfide concentration of 100 μg/liter was reported after such a plastic pipe had been in contact with static water (Mazaev and Slepnina, 1973); while studies by Health Canada found mono- and dibutyltin in potable water in PVC and CPVC pipes in the ng/liter range (Forsyth and Jay, 1997; WHO report, 2004). In similar studies (Sadiki, 1996; Sadiki and Williams, 1996, 1999) the majority of samples were found to contain levels below the limit of detection (of 0.5 ng/liter specifically); the same group later reported 28.5 ng/liter, (Sadiki and Williams, 1999). These values were found to increase with increasing time of contact, if conditions are stagnant.
Organotins are labeled as toxins that tend to be primarily distributed in the liver and kidney following oral administration to rodents (Evans et al., 1979; Mushak et al., 1982; Ehman et al., 2007), and the thyroid glands (Penninks et al., 1987). Dibutyltin dichloride (DMTCl) is reported as maternally toxic, but not teratogenic, at 20 mg/kg of body weight per day intake (Noda and Morita, 1994).
Although there are no direct adequate studies for the effects of dialkyltins on humans, human exposure to these compounds through drinking water is likely to be very low, apparently considerably less than 1 μg/day. The German Federal Institute for Health Protection of Consumers and Veterinary Medicine published a tolerable daily intake of 0.25 μg/kg body weight per day for butyltin compounds (BGVV, 2000). This value was also reported in an English journal for the first time in 2003 (Rudel, 2003). There are several studies surveying the organotin compounds in reservoirs supplying drinking water (Nikolaou et al., 2007).
Secondly, it is well known that PVC, the parent compound of CPVC, can leach vinyl chloride monomer (VCM) into the environment, including into drinking water if pipes are considered. VCM is listed as a carcinogen by OSHA (the Occupational Safety and Health Administration) and NIEH (the National Institute of Environmental Health) (NIEH report, 1997), causing VCM tumors of the liver, brain, lung, lymphatic and hematopoietic system. A study found that after 30 days of exposure, VCM concentrations leached from PVC pipe were generally greater than 2.5 μg/liter (Al-Malack et al., 2000), which is higher than established (safe) values (0.5–2 μg/liter). Being derived from PVC, CPVC is expected to have the same monomer and dangers associated with it.
Thirdly, thermal decomposition, combustion or pyrolysis products of CPVC from fire (Fardell, 1993) include several hazardous gases, such as carbon monoxide, carbon dioxide, hydrogen chloride and small amounts of benzene, aromatic (and aliphatic) hydrocarbons, small amounts of chloroform and carbon tetrachloride, in addition to organotin and hydrocarbon compounds. Irritating peroxide fumes are formed when CPVC is heated up to and above its thermal decomposition point. It is well known that both PVC and CPVC have restricted thermal stabilities because of their tendency to dehydrochlorination. In fact, if thermal decomposition/degradation products of CPVC are considered to be similar to those of PVC, in addition to these chemicals there should be:
• VCM (considered as a carcinogenic and systemic toxin, as described above)
• HCl and phosgene (considered as mucous membrane and respiratory irritant)
• Dioxins, furans, PBTs (persistent bioaccumulative toxicants) and PCBs (polychlorinated biphenyls).
All are considered as potentially carcinogenic (Burke et al., 2001; Ammala et al., 2011).
Inhalation of decomposition (and/or combustion) products causes irritation of the respiratory tract, eyes and skin. Depending on the severity of exposure, physiological responses will be coughing, pain and inflammation. Chronic exposure to fumes and vapors from heated or thermally decomposed CPVC may cause an asthma-like syndrome due to the inhalation of process vapors or fumes. Due to the possible effects of CPVC on health, which is a controversial issue, its use in PVC applications for cables as a flame retardant is decreasing.
Fourthly, CPVC piping and fittings are joined with CPVC cements, which can be a one-step or two-step process. The two-step process additionally requires the use of a primer. Most of the solvents that are used in pipe cements, primers and cleaners are considered as eye irritants. To be more specific, primers that contain solvents are acetone (0–1%), tetrahydrofuran (THF, 4–40%), methyl ethyl ketone (MEK, 30-85%), and cyclohexanone (5–15%). In addition, there may be disinfection by-products (DBP) including trihalomethanes (THM) such as chloroform, without mentioning that chloroform and vinyl chloride monomer may be found in the pipe itself. All of these chemicals are leachable into drinking water for long or short periods of time depending on the conditions. And among these solvents, THF raises more serious health concerns, as it is a known carcinogenic compound. Most of the solvents used in pipe cements, primers and cleaners are eye irritants.
Aiming to force the development of low-emitting/leaching CPVC piping materials, adhesives, sealants and primers are expected to comply with the ‘South Coast Air Quality Management District (SCAQMD) Rule No. 1168’ (effective as of 1 July 2005) in the USA, and for CPVC welding, a maximum VOC limit is put at 490 g/liter, less water.
3.2.3 CR (CAS number: 9010-98-4)
CR (chloroprene rubber, polychloroprene, poly[2-chloro-1,3 butadiene], also known by the generic names of first ‘DuPrene’ and later ‘neoprene’, is composed of mostly trans-1.4-polychloroprene with the formula [CH2–CCl = CH–CH2]n. It is an important diene-based elastomer produced from its monomer chloroprene, 2-chloro-1.3-butadiene, by free-radical emulsion polymerization (Campbell, 2000). Polymerization appears to take place almost entirely in the trans-1,4 form with some cis-structures, and CR is a crystallizable elastomer.
Vulcanization of CR is different from conventional methods, because electronegative chlorine interferes both with the double bond and with the a-methylenic group by deactivation, so that the common vulcanizing agent sulfur is ineffective and/or slow for the CR case. CR can be vulcanized by heating with zinc and magnesium oxides alone, by rearrangement and chlorine removal. This is exactly the same strategy employed for some of the other chlorinated polymers, i.e. CSPE.
CR is an extremely useful synthetic rubber, developed in 1931, and it was the first specialty elastomer with an annual consumption of above 3 × 105 tons worldwide. CR is mainly produced in the US, Germany, Japan, and China, and its largest consumption is in the US, China and the EU. CR was particularly useful in the Second World War as an artificial rubber with good weathering properties and resistance to heat and oil.
For rubbers or elastomers, low values for Tg are essential. Most such materials have the general formula − [CH2 − CH = C(X) − CH2]n−; however, in the case of chloroprene rubber where X = Cl, the size of Cl is relatively large and polar, hence the Tg value of CR is not expected to be too low. In fact it is − 20 °C, compared with two common rubbers − BR (butadiene rubber) or poly(cis-1,4-butadiene), where X = H and Tg is -108 °C; and NR (natural rubber) or poly(cis-1,4-isoprene), where X = CH3 and Tg is − 66 °C.
CR has perfect mechanical properties and fatigue and tear resistances which are second only to those of NR, with excellent oil, chemical and heat resistances, low flammability, high ozone and weather resistance. CRs are widely used in general engineering applications, such as in the production of dipped articles (e.g. gloves), wraps and sheets, as improvers of bitumen, as the base material for (solvent- or water-based) adhesives, in various molded goods, in cable coatings, transmission/conveyor belts and profiles, and primarily as the material for gaskets, tubing, O-rings, seals, weather stripping and hose (for gasoline).
The damping capacity of CR is fairly high. Its low permeability to water makes it suitable for sealer-type finishes for masonry and concrete. Unlike many other elastomers, CR vulcanizates already have high tensile strengths in the absence of carbon black and no reinforcing effect is found with any filler.
Some specific physical and mechanical values of CR pure gum vulcanizates are given in Table 3.4.
Table 3.4
Some physical and mechanical values of CR pure gum vulcanizates
| Density | 1.23 g/cm3 |
| Glass transition temperature | –20 °C |
| Melting point | 40 °C |
| Lower and upper use temperatures | –35 °C and 180 °C (continuous high temperature limit: 120 °C) |
| Tensile strength at break | 19 MPa |
| Elongation at break | 800% |
| Modulus (at 300% elongation) | 4.3 MPa |
| Hardness (Shore A) | 50 |
| Resistance to acids, alkalis, gasoline and oil | Good |
| Resistance to aromatic hydrocarbons | Fair |
| Resistance to ketones and chlorinated solvents | Poor |
| Resistance to oxidation and ozone | Excellent |
| Resistance to gamma irradiation | Poor |
| Resistance to flame | Good |
Although specifically known and used for its oil resistance, CR is also a very good general-purpose rubber that can replace NR in most of its uses. Some 60% of CR produced is being used in the rubber industry for products such as molded goods, cables, transmission and conveyor belts. CR has been shown to make excellent tires (but cannot compete with other elastomers in price).
CR is also a very important source as a raw material for adhesives (both solvent-based and water-based as well as contact adhesives, ca. 33%). CR contact adhesives are used for bonding high-pressure laminates, automotive trim, roofing-membrane attachment, furniture, kitchen cabinets, custom display cabinets, interior and exterior panels, wall partitions, etc.
Different latex applications of CR are well known (ca. 6%). CR latexes are mainly aqueous colloidal dispersions of CR or of copolymers of it with other monomers (such as methacrylic acid or 2,3-dichloro-1,3-butadiene), which are used for various bonding and adhesive applications as well as for production of dipped goods that require toughness in the unreinforced film, e.g. gloves. CR latex uses include adhesives, binders, coatings, dipped goods, (elasticized) improved asphalt and concrete, and foams. Tough crystalline CR polymers are in general preferred for adhesives; whereas softer, more flexible polymers are preferred for mechanical goods applications which can be compounded and fabricated for manufacture of rubber goods by molding, extrusion, or calendering operations. Other uses of CR include wire and cable coatings, industrial and gasoline hoses, coated fabrics, gaskets, tubing, O-rings and seals.
Civil engineering and construction studies in general require elastomers with exceptionally good resistance to weathering, long-term flexibility and good mechanical properties; and CR answers to all such needs. Extruded neoprene water stops, with dumb-bell center bulb cross-sections, are extensively used for contraction and expansion joints in concrete roofs, walls and foundations for sewage plants, bridges, overpasses, viaducts, tunnels, piers, dams, reservoirs and many other structures. Glazing neoprene gaskets are successfully used to accommodate thermal movements with retained elasticities. The lockstrip-type neoprene gaskets are particularly effective and also simple to install in construction applications. Preformed CR elastomeric joint seals are used for concrete pavements.
Various formulations based on neoprene are also used extensively in building adhesives, corrosion-resistant coatings, and a variety of mastics and waterproofing compounds, as well as several specific applications such as weather stripping for fire doors and noise isolation (i.e., for floating floors). One of the best known uses for CR fabric is for (scuba diving) wetsuits and orthopedic braces.
CR is considered as not classifiable as to its carcinogenicity to humans, if pure; and it is not considered as toxic. In fact, major CR types are on the approved list of the FDA (Food and Drug Administration of the US Department of Health, Education and Welfare). However, various processed CR products, including solid rubber goods and adhesives, may have a number of ingredients that may stay or evolve (as a gas) that can be hazardous, or may cause skin sensitivities, as follows.
Firstly, volatile ingredients that may exist in CR include mainly chloroprene monomer (CM), toluene and butadiene (BD), in most cases, in addition to some lead-containing products (i.e., lead oxide) used as compounding agents, and thiourea and lead from the curing system (Ethylene Thiourea, Report on Carcinogens, 2002), and all of these may be left in the system even in small (trace) quantities.
Among these, CM is a volatile and highly reactive chemical, with an estimated residence time in the atmosphere of 4.8 hours, and a recognized carcinogen. It is also suspected to be a strong toxicant (specifically towards cardiovascular, blood, endocrine and neuro systems) that affects liver and kidney at high levels of acute exposure. CM is a federal hazardous air pollutant and was identified as a toxic air contaminant in April 1993 under AB 2728 in the US. CM vapors are irritating to the eyes and respiratory tract at very low concentrations. It is a central nervous system depressant at high levels.
BD is listed by the EPA as a toxic pollutant. It is used during production of CR and small quantities may remain in the bulk CR as impurities and be released as a gas during processing of CR (or later while standing). A study conducted at the EPA’s Atmospheric Research and Exposure Assessment Laboratory showed emission levels of BD at 2–40% when processing CR (US EPA, 1985). Acute low-level exposure to BD causes irritation of eye, throat and other respiratory tract, and acute high-level exposure may cause nausea, lowering of the pulse and damage to the central nervous system. It is still debatable whether BD is a true carcinogen or not.
Both thiourea and lead compounds are known to be hazardous to health. Lead and its compounds (mainly lead oxide as mentioned above), irrespective of whether water soluble or not, are poisonous to humans, especially lead oxide. Exposure is mainly by inhalation, concentrated in soft tissues, mainly in liver and kidneys; it acts as a cumulative poison (Akovali, 2007).
Secondly, CR adhesives may contain rosin or colophony (ca. 4%), which is a skin contact sensitizer. The EU states that a colophony level of 0.1% or greater must be labeled as a potential skin contact sensitizer (EU Dangerous Preparations Directive 1999/45/EC, 2002).
Thirdly, the solution-bonding adhesives of CR, in the case of traditional solvent-based ones, usually contain a mixture of solvents (including a ketone or an ester, an aromatic and an aliphatic hydrocarbon such as naphtha, naphthaline, hexane, acetone, methyl ethyl ketone (MEK), benzene, and toluene); while pressure-sensitive and contact adhesives contain zinc oxide and styryl phenol. Almost all of these chemicals are toxic to humans, and benzene is carcinogenic (Akovali, 2007). Rubber and gasket adhesives usually have solvents like hexane, naphtha, acetone and zinc oxide. Modified CR adhesives that contain water as the solvent do not pose such problems.
Fourthly, although CR has very low oral toxicity in general, it may cause mainly irritation and skin allergic reactions (for those with allergies or sensitive skin) upon direct contact or from wearing clothing, using gloves, boots or support braces made from PC fabric, i.e., dermatitis. This may be due to the thiourea left unused after vulcanization.
Fifthly, CR contains chlorine and there is a high possibility of dioxin release throughout its lifecycle, resulting from either manufacturing practices or from its intentional or unintentional combustion, i.e., fire. Dioxin is known to be a highly toxic chemical and a proven carcinogen to humans (IARC Group 1 carcinogen) (Akovali, 2007). Furthermore, if PC is burned in a fire, hydrogen chloride (HCl) gas is released, which is considered a severe eye and respiratory irritant.
3.3 Alternative materials
Although it is very difficult to replace completely the use of CPE, CSPE, CPVC and CR as construction materials in all aspects of performance and economy with safer plastics, several suggestions can be made:
• First of all, whenever possible, carefully selected and prepared completely pure versions of polymers which may cause VOC emissions as low as possible can be selected, preferred and used, although this may prove uneconomic.
• TPO (thermoplastic polyolefins) and EPDM (ethylene propylene diene monomer, ‘M class’, with a saturated chain of the polymethylene where ethylene content is 45–75%) both fulfill the criteria for single-ply membrane roof waterproofing applications, are readily available and are quite cost-competitive.
• Window treatments are available in TPO, fiberglass and polyesters.
• For plumbing, HDPE or PP can offer other alternatives.
• Materials such as PP (polypropylene), HDPE and EPDM are commonly available alternatives to CSPE and to CR in geomembrane applications.
• For soundproofing, for ultimate flooring and wall noise barrier systems for airborne sound control, either MLV (mass loaded vinyl barrier), green glue (a water-based viscoelastic damping compound) or cotton fiber can be considered in place of CR. Among these, probably the second and third (or their combination) can be more economically viable options.
• Solvent-based adhesives of PC can be avoided as much as possible, and can be replaced with those of all water-based ones; while as alternatives to CR contact adhesives, PU (polyurethane) and styrene block copolymers can be considered.
3.4 Sources of further information
Some suggestions for PBT (persistent bioaccumulative toxicant)-free building materials are as follows:
• GreenSpec Product Directory: <http://www.buildinggreen.com>
• Healthy Building Network, PVC free building materials chart: <http://www.healthybuilding.net/pvc/alternatives.html>
• Health Care Without Harm, Green Building: Alternatives to Polyvinyl Chloride (PVC) Building Materials for the Neonatal Intensive Care Unit (NICU) (includes information on PVC and HFR content): <http://www.noharm.org/details.cfm?ID=1339&type=document>
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