Neat Plastics

Identifies a plastics with Nothing Else Added To. It is a true virgin polymer since it does not contain additives, fillers, etc. These are very rarely used. 

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In addition to the broad categories of TPs and TSs, TPs can be further classified in terms of their structure, as either crystalline, amorphous, or liquid crystalline. Other classes (terms) include elastomers, copolymers, compounds, commodity resins, engineering plastics, or neat plastics. Additives, fillers, and reinforcements are other classifications that relate directly to plastics properties and performance. 

Table 6.37 compares some properties of conductive and neat plastics. 

K. J. McGrath and R. G. Weiss, Rate of chair-to-chair interconversion of cyclohexane-d in the neat plastic crystalline phase.. Phys. Chem., 1993, 97(11), 2497-2499. 

Most neat plastic materials used for packaging of pharmaceutical products absorb UV-VIS radiation below 280 nm. Therefore, photostabilization by plastic packaging is only possible by the addition of colorants, UV absorbers, or pigments to the plastic mass. 

Year Market ( billion) Wood Neat plastic WPCs... 

For neat plastics, the CTE is about twice as much compared with WPC boards, which are about 50% filled with nonplastic materials, which is wood liber and sometimes minerals. As the coefficients of expansion-contraction of both wood fiber and minerals are about ten times lower than those for WPC materials, hence, the reduction in the coefficient s value for filled WPC. In reality, the picture is somewhat more complicated because it is the expansion-contraction of wood along the grain that is 10 times lower compared to common WPC. Expansion-contraction of wood across the grain is close to that of WPC. That is, an orientation of wood fiber in a WPC material can increase or decrease the coefficient of expansion-contraction. 

Neat plastics (except nylons), which are used in composite materials, practically do not absorb water (hundredth or thousandth percent by weight). Incorporation of cellulose fiber into plastic significantly increases water absorption (0.5-2% for 24 h underwater), which is still much lower compared to wood itself (typically more than 20% w/w for 24 h underwater). 

Cellulose fiber is a good reinforcing tiller. In fact, this is one of the two major factors of the very existence of WPC materials (a) to make the composite material less expensive and (b) to obtain material with overall better properties compared to neat plastic, on the one hand, and wood, on the other. For example, tensile modulus of a particular sample of neat polypropylene was 203,000 psi, whereas for the same polypropylene filled with 40% of jute it was 1,030,000 psi. For a comparison, for the same polypropylene filled with 40% glass fiber it was 1,100,000 psi. Tensile modulus for natural fiber itself is in the range of 3,800,000-17,400,000 psi [135]. Table 3.4 shows data in more detail. 

Table 3.12 shows that the melt flow index of HDPE in the presence of 50% wood flour decreases rather significantly, from 1.6 g/10 min for salt cedar to 0.2 g/10 min in the presence of pine. Fnrthermore, if we consider the initial MFI value for the neat plastic, a drop in MFI is qnite significant. For example, a polypropylene with MFI 23 g/10 min (MFI was 29 g/10 min after processing in the extruder at 100 or 300 rpm) was loaded with 20% bleached sulfite cellulose fibers, and after extrusion at 100 rpm MFI dropped to 2 g/10 min. With 30% loading with the fiber, MFI further decreased to 0.5 g/10 min [131]. 

Like many minerals, mined from natural sources, talc typically contains some admixtures that can canse plastic oxidation and degradation dnring processing and at the end-use service. Hence, when talc is added to a polymer, it reqnires more antioxidants (compared with neat plastic), a necessary amonnt of which can vary with different talcs. 

In a combination of fly ash and wood flour in HDPE-fllled composite, fly ash was making the material weaker and more flexible compared with only wood flour-filled HDPE (Table 4.20). However, fly ash makes the filled material stronger and stiffer compared with the neat plastic. 

Because fly ash is not a real, active flame retardant, plastics filled with it typically have practically the same ignition point and only slightly higher flame spread index compared to the neat plastic. 

However, in reality a profile coming from the die is forcefully cooled, often using a water bath. Polymer molecules oriented along the flow are frozen in the thermodynamically unfavorable state and cannot move noticeably until temperature is up again. This is related to polymer molecules in both a neat plastic and plastic-based composites. In such a frozen state composite deck boards are often placed into a warehouse and eventually sold to an end user, a customer. 

Table 10.5 shows a collection of data on coefficients of expansion-contraction for WPCs, including commercially available ones, and for some neat plastic lumber boards, as references. 

UC Forest Products Laboratory (UCFPL) has undertaking fire performance testing of neat plastic and WPC deck boards. The testing was conducted in 2002. Table 14.16 and Figures 14.1 through 14.10 summarize and illustrate main results of the test. 

In this respect a WPC board is principally different from boards made from neat plastic. In neat plastic, oxidation of the material takes place only on the surface. In the bulk, oxidation goes in severe oxygen starving conditions. WPCs typically have porous matrix, hence, a rather significant water absorption. If water is absorbed so weU, oxygen is absorbed much faster, because it has smaller, easily diffusible molecules. 

The oxidative degradation capacity of tillers, inorganic (metal oxides, particularly free metal-containing) colorants, and other additives in WPC is greatly underestimated by many researchers and manufacturers of composites. Composite materials generally require much more antioxidants compared to neat plastics, particularly when an energy-intense compounding is employed. 

Upper layers as well as in the bulk of the material. Hence, different kinetics and sometimes different chemistry of photodegradation of WPC compared with those of neat plastics. 

Besides, fading of WPCs is different from that of neat plastics. Wood affects fading of composites. There is not enough data accumulated with WPC in order to answer those questions. 

The Power-Law Index of Some Neat Plastics As it was explained in the section Shear-thinning Effect and the Power Law Equation, the higher the deviation of a molten plastic from Newtonian behavior, the lower its power-law index and the steeper the dependence of its viscosity on shear rate. The lower the power-law index, the more sensitive the shear viscosity to flow speed. As it will be shown in this chapter later, the lower the quality of a regrind, the lower (often) its power-law index. As can be seen from Tables 17.4 and 17.5, PVC, PS, ABS, and PMMA have particularly low power-law index compared to PET or PE, hence, that lowers the window of processability for the former plastics in terms of speed. Both the... 

Viscosity and the Power-Law Index of Wood-Plastic Composite Materials Let us consider in more detail how fillers tend to make the system more shear thinning, that is, to decrease the power-law index. At lower shear rates or frequencies, neat plastics often exhibit a Newtonian plateau, that is, a higher apparent power-law index, and in the presence of fillers, the plateau often turns upward or even disappears. In other words, the addition of filler often makes the power-law plot more steep, that is, shifts it to a more uniform straight line dependence of viscosity verses shear rate (or frequency). 

Dynamic rheometry was not (and, apparently, cannot be) employed for studying melt fracture of neat plastics and composite materials. This has been done so far only using capillary rheometry. However, dynamic oscillatory measurements can produce the most reliable rheological data on filled polymers [2,4]. It should be noted that measurements at dynamic oscillatory conditions bellow frequency of 0.1 rad/s likely produce erroneous results due to the increased time for reaching steady state at low frequencies [4]. 

Capillary Rheometer and an Extruder Are They in Agreement One can ask a reasonable question If rheology data are obtained in a capillary rheometer, are they applicable to an extruder To answer this question, at least for a specific set of conditions, a direct comparison was made [31]. It was found that the capillary rheometer and extruder are in good agreement for neat plastics (polystyrene and polypropylene), but extruder systematically measures lower viscosities in glass-fiber-filled plastics. 

Melt fracture for highly filled composite materials has a more complex character compared to that of neat plastics. And this is, of course, due to the effect of the filler. For example, using a cone die (the entrance diameter 2.5 in., the exit diameter 0.300 in., the length of the die 12 in.) it was shown for the neat HDPE that there was no visual signs of extrudate distortion for any of the flow rate tested (5.5-177 g/min), unlike that for filled plastics. Similarly, the 10%-filled (ground rice hulls) HDPE did not exhibit any observable extrudate distortion. However, the 60% -filled composite... 

Flexural modulus, effect on, 154, 155 Flexural strength, effect on, 154, 155 Water absorption, effect on, 154, 155 Naphthalates, 203 Narrow MWD polymers, 650 National Institute of Standards and Technology, 376 Natural fiber, 11, 125 Natural graphites, 80 Natural weathering, 592 Near infrared spectroscopy, 186 Neat plastics, 21, 258, 259, 268, 276, 278, 280... 

Power-law index, neat plastics, 635 Precipitated silica, 128, 146 Premier, 597, 600 Preservatives, 415... 

Operation Neat plastics recyclii Mixed plastics recycling Hydro- genation Neat plastics thermolysis Mixed plastics thermolysis Gassifi- cation Incine- ration Bnrning LandfiU... 

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