Recycling of Plastic Materials Part 9 ppsx

The table shows polymers employed in a car respectively in 1980 and 1990, clearly demonstrating the rapid growth of the polypropylene materials.. 130 Processing of Mixed Plastic Waste Ta

To develop this concept Himont and CSI have divided their research project into two main tasks:

• to develop new advanced polypropylene materials

• to promote new technologies

Although many different polymers are used in cars today, the industry tends to favor more and more polypropylene use due to a large range of properties avail-able Polypropylenes became standard of reference where aesthetic quality, structural properties, easy processing, and recyclability must blend harmoni-ously into the requirements of every individual item These phenomena are il-lustrated by data in Table 5 and Figure 5 The table shows polymers employed in

a car respectively in 1980 and 1990, clearly demonstrating the rapid growth of the polypropylene materials Figure 5 shows the trend for polypropylene in vari-ous parts of a car: from 1990 to 1995, analysts predict an increase from about 22.4 kg per car to around 38.0

130 Processing of Mixed Plastic Waste

Table 5

Plastic consumption by car industry in Western Europe

Although there is an increasing interest in the use of these materials for body-work elements, the largest contribution to this growth (9.1 kg) will be from car interior components as a result of large-scale replacement of more traditional materials

CONCEPTS FOR CAR INTERIORS

New developments in polyolefin-based materials have created a family of poly-propylene products with a wide range of physical properties, including the abil-ity to be easily recycled When utilized by automotive and product designers as a part of a “design for disassembly” strategy, these compatible materials will yield large sub-assemblies that can be reclaimed with a minimum of handling.1-5

In each project, the design incorporates readily identifiable hard point connec-tions between the polypropylene components and the metal automobile subframe This will allow personnel in recycling centers to remove these parts quickly, and in large pieces that can be completely reground and recycled The concept presented here has been applied to car dashboards and such interior ve-hicle components, like floor covering, trim, and door panels as well as bumpers Figure 5 Advanced materials used for vehicles.

TPO BASED MATERIALS

Thermoplastic Elastomers (TPE) are classes of heterophasic polymers, charac-terized by thermo-reversible interaction among the polymeric chains The new polymeric materials that are considered to produce easy recyclable automotive systems, can be defined as a sort of a new generation of Olefinic Thermoplastic Elastomers (TPO), belonging to a broad family of polyolefinic alloys that can now be produced directly during the polymerization phase These completely new materials, resulting from advanced research and development carried out

by HIMONT, can be tailored in order to meet different requirements of most of car applications The basic partly finished components suitable for the construc-tions of the main automotive composite structures will be described

Synthetic leather

The TPO synthetic leather was produced from a resin studied to have a good processability both by extrusion, the traditionally utilized for polyolefins manu-facturing, and calendering, the most employed technology in producing PVC and PVC/ABS synthetic leathers.1

The embossing, as well as the coupling with a large variety of different layers (e.g films, woven and non-woven structures, foams sheets) can be easily ob-tained in line, using traditional technologies The thermoformability of the TPO based synthetic leather is excellent as well as the graining

Tensile strength, flexural modulus, puncture strength, scratch, and marking resistance at low, as well as at elevated temperatures, are better than those of synthetic leathers present in the market Outdoor ageing and accelerated UV tests indicate that this material can well overcome the severe conditions pro-duced by the tendency to increase the oblique angle of car windshield Same characteristics of the TPO based synthetic leather are reported in the Tables 6-8

Foam sheets

The technology used for the production of TPO based foam sheets cannot be fully disclosed here The research guidelines were principally oriented to over-come some limitations in physical foaming of polypropylene, related to intrinsic rheology and kinetics of crystallization.2These materials present a loss of stiff-ness quite abrupt near the melting point, due to the melting of a crystalline

132 Processing of Mixed Plastic Waste

dition for expansion that could be obtained only in a narrow temperature range Hence the problem is to improve dramatically the strength-temperature proper-ties near the melting point The rate at which polymer crystallizes from melted state is the other important physical property in the foaming process For in-stance, polypropylene crystallizes much slower than polyethylene This means

an increasing of the time required to build up sufficient modulus to avoid cell-wall rupture and cell-coalescence during the expansion which is a serious process limitation to overcome

The cushioning and soft-feeling properties required for some car interior appli-cations were achieved by matrix modification as well as by the structural pa-rameters affecting the compression-deflection of the foamed material2 (i.e density, open cell content, cell size)

Table 6

Properties of TPO material

Specific gravity Melt flowrate Flexuralmodulus Vicat 1 kg HardnessShore D Elongationat break ASTM method D-1505 D-1238 D-790 D-1525 D-2240 D-639

Table 7

UV resistance of HIFax CA12A (UV exposure in Xenotest 1200 according to ISO-4892)

structure The consequence of a rapid change in modulus is an unfavorable

In order to obtain all TPO recyclable applications described below, different as-sembling techniques have been specifically studied to obtain the basic composite structures.3,4The most interesting technique is one that allows to obtain simul-taneously thermoforming, embossing, and coupling in one stage operation

yield-134 Processing of Mixed Plastic Waste

Figure 6 Dashboard sketch. Figure 7 Sketch of floor covering.

Table 8

Fogging test for HIFax CA12A skin (transmittance measured according to DIN 75201-C)

Transmittance (%)

ing a foamed-synthetic leather bilayer on a rigid support (all TPO based)

without adhesives This process can eliminate problems of embossing distortion present in thermoforming of an embossed synthetic leather

AUTOMOTIVE APPLICATIONS

Dashboard

Figure 6 shows a sketch of the dashboard designed for recycling and obtained with a process based on the previously described assembling technique The sys-tem has three basic components, that, in the past were made of different materi-als; in a new design this system has been molded from TPO based polymers to provide rigidity, comfort, safety, and aesthetics Some prototypes have been re-cycled following the traditional procedures for the scrap recovery of thermoplas-tic materials The mechanical characteristhermoplas-tics of the obtained materials are reported in Table 9

Floor covering

The structure proposed does include a lower high density TPO based sheet, an intermediate polypropylene felt layer, and a polypropylene fiber carpet ( loop pile or cut pile ) on the top A sketch of this component is shown in Figure 7 The recovery possibilities of the scraps from the sandwich production (about 20%) and material coming from the whole structure are the following: after passing through a mechanical mill, the material can be calendered and then processed

by injection molding as well as mixed with virgin polypropylene and afterwards

Table 9

Properties of PP recycled from dashboard

Method Units Recycled material Standard PP

cussed above, have been usefully utilized to produce the lower layer of the floor covering and have met the required specifications The characteristics of the re-cycled materials are reported in Table 10

Other components

All the other interior components are now being designed following this ap-proach procedure:

136 Processing of Mixed Plastic Waste

Table 10

Properties of PP recycled from floor covering

Figure 8 Door panel prototype.

extruded Materials, obtained from sandwich samples and processed as

dis-Door-panels - Polypropylene materials allow the production of integral

struc-tures of aesthetic and functional elements produced within the same family of

materials The frame and the arm-rest are obtained by injection molding of glass filled PP Trim parts are produced in lightweight panels of thermoformed sheets which are laminated with fabrics, calendered film materials and/or carpeting

PP air ducts are also included Figure 8 shows a prototype of a door-panel

Pillar Trim & Rear Shelf - Blow molding has been used for the pillar trim to

provide the double functions of air ducting and aesthetic trimming Finishing is provided during the molding process with an application of fabric or textured film The support structure may be filled or unfilled types, depending on the me-chanical properties required For the rear shelf, the design presented is a vac-uum formed laminate of extruded PP and woven fabric

CONCLUSIONS

• The general solution to the problem of plastic recycling at the life-end can-not be unique and some suitable approaches have been studied, depending

on application sectors

• Although mixed plastics can be processed and recycled through some tech-nologies, the use of homogeneous or compatible plastics seems to be the most suitable way to allow a direct and more profitable recycling

• Recent technological advances have made available thermoplastic families

of materials that can be tailored in order to meet different requirements of each application sector

• It is possible to design automotive structures, for instance, made of the same chemical material and provide an important aid to the recycling of plastic

REFERENCES

1. J C Haylock, A Addeo, and A J Hogan, Thermoplastic Olefins for Automotive Soft Interior Trim, SAE International Congress and Exposition, Detroit, Michigan,

February 26 - March 2, 1990.

2. A Addeo, Mechanical Energy Absorption by Plastic Foam, Sitev Forum, Geneve

15-18 May 1990.

3. A Addeo, Novel TPE for Car Interior Trim : a PVC Replacement, TPE 90 Deaborn,

Michigan, March 28-29,1990.

4. A Addeo, New Materials for Automotive Interiors, 22nd ISATA Florence, Italy 14-18

May, 1990.

5. F Forcucci, D Tompkins, and D Romanini, Automotive Interiors Design for

Recyclability, 22nd ISATA Florence, Italy 14-18 May, 1990.

The Use of Recyclable Plastics

in Motor Vehicles

Michael E Henstock and Klaus Seidl*

The University of Nottingham, Nottingham NG7 2RD, England

*BMW, Section EG-554, München, Germany

INTRODUCTION

In market economies recovery operations are judged on financial criteria Thus, whether or not a discarded waste is exploited for the materials it contains depends, among other things, on the technical ease of recovery of a saleable sec-ondary product Since industry must also consider the environmentally-sound disposal of its residuals the ease of residuals disposal is financially important.1

RECOVERABLE MATERIALS IN THE MOTOR VEHICLE

Discarded vehicles yield ferrous metals, aluminium, copper, lead, and zinc However, as currently processed by shredding, they also generate a valueless

fraction, containing the non-metallic detritus of seats, carpets, tyres, and other

components The historical position of steel in the automotive scrap industry emerges from data for the composite car described in the pioneering work of Dean and Sterner.2The recovered steel, even when contaminated with the re-sidual copper in the car, would have generated 43% of gross revenue in 1969, 60% in 1976, and 56% in 1986 at prevailing metal prices for those years.3

PRESENT RECOVERY PRACTICE

A discarded vehicle may first be stripped of resaleable parts by a salvager (wrecker) or dismantler, or it may go directly to a scrap processor, who may or may not strip such parts before processing the hulk Until some twenty years ago processing usually took the form of compression into a cuboid or rectangular bale, known in the USA as a No 2 bundle, and in the United Kingdom as a No 5 bale Sometimes, where air pollution regulations permitted, the hulk was incin-erated to remove non-metallic items, but since this step involved cost it was

ten omitted The bale, containing all the non-ferrous and non-metallic materials

that it had not been worthwhile to remove, was then charged to a steelmaking furnace Because it is impossible to inspect the interior of bales their purity is unknown and their desirability limited Hence, this procedure is now much less common

Early in the 1960s the market was considerably disturbed by the introduction

of the scrap shredder, which comminutes feed, including whole vehicles, to frag-ments some 5-20 cm in diameter For physical and chemical reasons steel mills usually prefer shredded scrap to bales Hence, shredded steel scrap enjoyed a rapid rise in popularity and market The shredder generates, however, a non-metallic residue, currently worthless, whose disposal involves cost

In 1991 there is, however, increasing realization that shredding, though offer-ing financial advantages over baloffer-ing so far as materials recovery is concerned, is nevertheless a noisy, energy-intensive, and self-destructive process There is, at last, some interest in designing road vehicles to make them easier to dismantle Ironically, far from being pleased by this prospect, some sectors of the scrap in-dustry view with disquiet the setting up, by certain vehicle manufacturers, of in-house recycling plants.4

CHANGES IN THE MATERIALS USED IN VEHICLES

Changes in vehicle materials are made for a variety of reasons, including cost, absolute performance, lightness, (to improve fuel economy), and longevity The magnitude of fuel savings over an estimated 174,000 km vehicle road life has been computed as 15-25 l/kg of weight saved.5,6Though improved engineering design may achieve weight reductions, a point is reached where further im-provements may be made only through the use of light materials Considerable effort has therefore been devoted to substitution of steel and cast iron by lighter materials, such as aluminium and polymers

Polymers are used in manufacturing for financial and technical reasons In transport they can provide reductions in the first cost.7Such cost reductions are not necessarily permanent, since technological improvements and shifts in the raw materials prices continually give one material a cost advantage relative to another Such a case is the substitution of plated ABS for zinc-based die castings

in trim However, plastics also offer other advantages: their use can achieve sig-nificant weight savings relative to metals and, whether for this reason or for oth-ers, they may offer substantial lifetime energy savings For example, it has been