Recycling of Plastic Materials Part 1 potx

Table of ContentsPolyethylene terephthalate Film Recycling 1 The Importance and Practicability of Co-injected, Recycled Polyethylene terephthalate/Virgin Polyethylene Manufacturing Proce

of Plastic Materials

Francesco Paolo La Mantia

Editor

ChemTec Publishing

All rights reserved No part of this publication may be reproduced, stored or transmitted in any form or by any means without written permission of copyright owner No responsibility is assumed by the Author and the Publisher for any injury or/and damage to persons or properties as a matter of products liability, negligence, use, or operation

of any methods, product ideas, or instructions published or suggested in this book.

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Canadian Cataloguing in Publication Data

Main entry under title:

Recycling of plastic materials

Includes bibliographical references and index

ISBN 1-895198-03-8

1 Plastics - Recycling I La Mantia, F P

(Francesco Paolo)

TP1122.R43 1993 668.4 C93-093134-3

Table of Contents

Poly(ethylene terephthalate) Film Recycling 1

The Importance and Practicability of Co-injected, Recycled

Poly(ethylene terephthalate)/Virgin Poly(ethylene

Manufacturing Process of Multilayer Bottles Containing Regrind 18 Drying of PET Resin and PET Flakes 18 Co-injection Molding of Virgin and Reground PET Flakes 21 Conditioning and Stretch-blow-molding 21

Trials of Co-injecting Virgin PET and Reground PET Flakes 22 Quality of the Raw Materials 22

Bacteriological Contamination 24 Contamination by Foreign Substances 25

Recycling of Post-consumer Greenhouse Polyethylene

Films: Blends with Polyamide 6 27

Recycling of Plastics from Urban Solid Wastes: Comparison Between Blends from Virgin and Recovered from Wastes

Impact Resistance 53

Management of Plastic Wastes: Technical

Recycling of Urban Plastic Wastes 60

Identification of Polymers Present in the Film Plastic Wastes

and the Rheological Behavior of the HDPE/LDPE System 64 Mechanical Behavior of HDPE/LDPE Blends 65 Microstructural Aspects of HDPE/LDPE Blends 70

Blends of Polyethylenes and Plastics Waste Processing

Blends Containing Calcium Carbonate 94

Techniques for Selection and Recycle of Post-Consumer

General Considerations 100

Hydrolytic Treatment of Plastics Waste Containing Paper 111

Processing of Mixed Plastic Waste 123

Mixed Plastics from Household Waste 123 Plastics from Industrial Sectors 129

The Use of Recyclable Plastics in Motor Vehicles 139

Recoverable Materials in the Motor Vehicle 139

Changes in the Materials Used in Vehicles 140 The Effects of Materials Substitution on Vehicle Recycling 141

Recyclable Plastics Components 146

Comparison of Virgin and Recycled HDPE 146 Comparison of Fluorinated and Unfluorinated HDPE 147

The Recycling of Material from Used Fuel Tanks 148

Ground Rubber Tire-Polymer Composites 153

Ground Rubber Tire Composite Behavior 154

Characteristics of Tire Particles 155

Matrix Modification 165 Ground Rubber Tire and Recycled Plastics 167

Quality Assurance in Plastics Recycling

by the Example of Polypropylene 171

Further Processing to Polypropylene Granulate 175 Quality Assurance To EN 29,000 PP 176

QA Element - Process Control 179 Quality Assurance in After-sales Service 182

Recycling of plastic materials is now an important field in the plastics indus-try, not just an activity born under environmental pressure The recycling pro-cesses include industrial operations in which secondary materials are reprocessed and/or monomers recovered for further polymerization; such pro-cesses are termed secondary and tertiary recycling

Although the plastics industry considered recycling for many years, attention was mainly focused on the recycling of industrial scraps and homogeneous post-consumer plastics which are easy to collect and reprocess More recently, the plastics industry accepted the challenge of recycling of heterogeneous plas-tic waste based on new technologies of separation and reprocessing

Scientific research, scarcely visible only a few years ago, is now a very active, fast-growing discipline, contributing numerous papers which appear in the sci-entific literature Several congresses and scisci-entific symposia are attended by specialists every year and new books on this subject demonstrate the great sci-entific and industrial interest in the recycling of plastic materials

This book is intended to focus on the state of the art in recycling, the most re-cent technologies of recycling, and some rere-cent scientific research in the field Polyolefines and poly(ethylene terephthalate) (PET) are the most frequently recycled polymers, and as such they are given significant attention in the re-search and technology which this book reflects Two reviews characterize the state of the art in PET recycling De Winter presents a review on recycling of PET film and Neumann on a co-injection technology which allows one to use re-cycled PET as an intermediate layer in bottles Both processes are common in in-dustrial practice and are thus able to offer an overview of experience in plastic recycling which is of interest in other areas of recycling as well Other references

to PET recycling are presented by Sereni and La Mantia, Perrone, and Bellio Polyethylene (PE) and other polyolefines are discussed from various angles La Mantia and Curto propose methods of recycling of photooxidized polyethylene in blend with Nylon 6 It is shown that the recycled PE behaves like a functionalized PE, having compatibilizing attributes due to which blends ex-hibit improved mechanical properties

Recycling of urban wastes is discussed by Gattiglia et al and by Laguna et al.

Generation source, separation possibilities, and cleaning technology are dis-cussed in relation to blend properties, such as rheology, morphology, and me-chanical properties Comparison is also made with blends having similar

composition but made from virgin polymers.

The major problems in recycling of mixed plastic waste are due to their inferior processability, which results in materials having poor mechanical properties

La Mantia et al and Vezzoli et al present experimental results which disclose

the possibility of obtaining recycled materials with acceptable properties from mixed plastic waste

Plastic wastes are often contaminated with paper Klason et al present an

in-dustrial method of reprocessing paper-contaminated plastic waste which does not require a difficult and costly separation process Instead, cellulose from pa-per is converted to a filler The method and equipment suggested allow for

excel-lent dispersion of in situ formed filler.

Recycling of plastic component from car scrap is a very important challenge for the plastics industry and car manufacturers, since the plastic content in cars is systematically increasing Henstock and Seidl show results on the recycling of

plastic fuel tanks, Oliphant et al describe the methods of application of ground discarded tires as a filler in polymer composites; Vezzoli et al present new

strat-egies of design of easily recyclable car interiors; while Heil and Pfaff show how battery recycling can utilize all initial components, offering quality assurance for recycled polypropylene

An alternative method of recycling of mixed plastic waste is based on a separa-tion of different components into homogeneous fracsepara-tions Sereni describes op-portunities in this area and interesting industrial equipment required for effective separation of PET and PVC

The above short summary shows that this book combines lessons from the past experiences of an industrial practice with evaluation of modern trends and cur-rent research in the field of plastic recycling

F P La Mantia

Palermo, September, 1992

Poly(ethylene terephthalate) Film Recycling

W De Winter

Agfa-Gevaert N.V., Research & Development, Septestraat,

B-2640 Mortsel, Belgium

INTRODUCTION

The impact of man-made polymers on the environment is a problem of high pri-ority in most industrialised countries Mainly due to a build-up of disposed waste in landfills, and due to campaigns in the press about mistakes made in the management of waste treatment, public opinion is focusing on this problem The fact that the corresponding percentage by volume is higher, due to the low pack-ing density of wastes, makes the problem more visible Although “plastics” con-stitute not even 10 wt% of the total amount of wastes, both residential and industrial, found in landfills (see Figure 1), public attention to them is increas-ing A possible explanation1of such a reaction suggests that there is a lack of compatibility of plastics with the environment, despite the fact that the majority

of products used in present daily life are made of materials which have also been manufactured by a chemical process

The plastic waste in landfills consists of about two-thirds polyolefines, and only ca 15 % of styrene polymers, ca.10 % of polyvinyl chloride, and less than

10 % of all other polymers, including poly(ethylene terephthalate) (PET) The largest use of PET is in the fiber sector PET film and PET bottles repre-sents only about 10 % each of the total PET volume produced annually.2It is also generally known that the total ECO-balance, considering energy consumption, atmospheric and water pollution, as well as solid waste content, is by a factor 2

to 5 more favorable for PET film than for its greatest competitors in the packag-ing sector, namely glass and aluminium.3

In addition, PET is one of the largest recycled polymers by volume,4because it

is suitable for practically all recycling methods.1PET recycling by the following technological processes is discussed below:

• direct re-use

• re-use after modification

• monomer recovery

• incineration

• and re-use in a modified way

In addition, attention will be given to some other attempts for recycling which have not been thoroughly evaluated so far, like biodegradability and photodegradation

This paper is limited to the discussion of PET-film recycling A global review of PET-recycling in the sectors of fibres, films, and bottles was published earlier.2

Figure 1 Composition of landfill-waste (domestic and industrial).

DIRECT RE-USE

Over 50 % of the PET film produced in the world is used as a photographic filmbase The manufacturers of these materials, mainly Agfa-Gevaert, East-man Kodak, du Pont de Nemours, Fuji, Minnesota Mining & Manufacturing, and Konishiroku have long been interested in PET film recovery An important motivation for the efforts made by these companies is the fact that photographic films are usually coated with one or more layers containing some amount of rather expensive silver derivatives, which have been recovered since the early 20th century, when cellulosics were used as a film base Silver recovery makes PET-base recovery more economical.5,6In a typical way of operation, PET film recycling is coupled with the simultaneous recovery of silver, as represented in Figure 2

Figure 2 Combined recovery of silver and PET.

In the first step of the process, photographic emulsion layers containing silver are washed with, for example, NaOH, and after separation, silver is recovered

on one side, and cleaned PET-waste on the other side.2Important in this process

is that the washed PET-film scrap is clean enough to be recovered by direct re-extrusion, although careful analysis remains necessary

Direct recycling of PET-waste in the molten state, before re-extrusion to PET-film, is of course the most economical process thinkable, as recovered PET-scrap can be substituted for virgin PET-granulate without requiring any additional steps It is well-known that PET in the molten state gives rise simul-taneously to polymer build-up and to polymer degradation, so that reaction con-ditions for this process have to be controlled very carefully in order to obtain an end-product with desired physical, chemical and mechanical properties, like color, molecular weight, and molecular weight distribution

A large number of reaction parameters have to be kept under permanent con-trol (temperature, environmental atmosphere, holding time in a melt state, amount of impurities, type of used catalysts and stabilizers, etc.) The order of addition of the PET flakes is very important A typical flowsheet of a batch-PET-process7is represented in Figure 3 In such a process, the PET-flakes can be added after polymerization, before the melt enters the film extruder screw (Figure 3, indication 1) Such a procedure, however, has two main draw-backs:

• a highly viscous melt is difficult to filter (to eliminate possible gels or microgels)

• resulting low-boiling or volatile side-products cannot be discarded any-more

In order to eliminate these disadvantages, several alternative operation modes have been worked out in the past A method to add recycled PET during

the esterification step (Figure 3, indication 2) has been described by du Pont.8In such a way filtration can take place in the low-viscosity phase, and volatiles can still be eliminated during the prepolymerisation phase

Although PET-recycling by direct re-use is by far the most economical process,

it is only useful in practice for well characterized PET-wastes, having exactly known chemical composition (catalysts, stabilizers, impurities) Therefore, this process is the most suited for the recovery of in-production wastes, but it may not be ideal for customer-recollected PET-film An industrial process for X-ray film-recycling was worked out by the IPR-company9and introduced to the mar-ket under the name REPET on the basis of a triple motivation:

• availability of the waste chips on a repetitive basis

• suitable purity

• very competitive price

Figure 3 Batch process flow sheet.

RE-USE AFTER MODIFICATION

Similar to the method described under direct re-use, in which PET-flakes are added during the esterification process, PET-polymer is broken down into low-molecular, low-viscous fractions Such method could already be viewed as a method of re-use after modification Because the intermediate products are not separated at any moment of the process, the degree of purity of PET-scrap must

be high

For PET-wastes having a higher degree of contamination, other technological processes are applied, including further degradation by either glycolysis, methanolysis, or hydrolysis,10yielding products which can be isolated The prin-ciples of chemical processes on which these methods are based are schematically represented in Figure 4

Figure 4 PET degradation by glycolysis, methanolysis, and hydrolysis.

Glycolysis can be considered as a method for direct re-use, whereas methanolysis and hydrolysis are mainly taken into consideration for monomer recovery, as discussed below

The du Pont Company published11many details concerning the glycolytic recy-cling of PET Less costly ingredients than those required for hydrolysis or methanolysis, and more versatility than direct remelt recycling are quoted as the reasons for glycolysis choice Goodyear has also developed the PET recycling process based on glycolysis which is called REPETE.12

Glycolytic recycling of PET, which can be done in a continuous or in a batch process, is preferentially performed by addition of a PET waste to a boiling eth-ylene glycol, which leads to the formation of low-molecular weight intermedi-ates and eventually to crystallizable diglycol terephthalate (DGT) The rate of the degradation reactions is primarily controlled by varying the holding time and temperature, which depends on a choice of suitable catalysts (e.g., titanium derivatives),12,13 and by adjusting the PET/glycol ratio It is also necessary to avoid side reactions which might occur, e.g., by adding “buffers” or by keeping down reaction time and temperature

The low-molecular weight depolymerizates can be introduced directly into a polymerization system,14preferentially after filtration In this method, particu-lar care has to be taken in order to avoid glycol ether formation, which may lead

to PET of inferior properties The glycolytic degradation can also be pushed to further completion, leading to DGT-recovery, rather than to direct re-use

In addition to the glycolytic recovery of PET for production of a new PET-film, granulate, or monomer (EG and DGT), alternative methods have been described for the preparation of so-called PETGs (i.e., glycol-modified PET), which can be used for different purposes.15,10Depending on the type of glycol (or polyol) used for depolymerization, and on the nature of dicarboxylic acid used for subsequent polycondensation, the obtained polyester may be used as a saturated polyester resin (e.g for films, fibres or engineering plastics), unsaturated polyester resin, mixed with vinyl-type monomers, or alkyd resin, where polycondensation is per-formed in the presence of tri- or poly-functional organic acids

Although this method for producing unsaturated resin, e.g., for use in regular castings or in fiber-reinforced laminates, has been thoroughly studied by PET-film manufacturers, it is believed that the method is not currently used in production.16