Plastic packaging materials for food : barrier function, mass transport, quality assurance, and legislation

1 1.1 1.2 1.3 2 2.1 2.1.1 2.1.2 2.2 2.2.1 2.2.2 2.3 2.3.1 2.3.2 2.3.3 2.3.4 2.3.5 2.3.6 2.3.7 3 3.1 3.1.1 3.1.2 3.1.3 3.1.4 3.1.5 3.1.6 3.1.7 3.1.8 3.1.9 3.1.10 Preservation of quality through packaging 1 Quality and shelf life of food Physical and chemical interactions between plastics and food Organization of the book 4 General Plastic/Packaging/Food References 8 1 4 Characteristics of plastic materials 9 Classification, manufacture and processing aids Classification and manufacture of plastics Processing aids 14 Structure and states of aggregation in polymers Structure 17 States of aggregation 19 The most important plastics 21 Thermoplastics 21 Thermosets 34 Polyurethanes 35 Natural and synthetic rubber 37 Silicones 38 Plastics based on natural polymers 41 Coatings 42 9 10 17 Additives for plastics and their transformation products 47 Additivs for plastics 47 Introduction 47 Nucleating agents 47 Lubricants 49 Antistatic agents 50 Blowing agents 51 Plasticizers 51 Stabilizers 53 Antifogging agents 64 Dyes and pigments 64 Fillers and reinforcing agents 65 x Contents 3.2 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6 4 4.1 4.1.1 4.1.2 4.1.3 4.2 4.3 4.3.1 4.3.2 4.3.3 4.4 5 5.1 5.1.1 5.1.2 5.2 5.2.1 5.2.2 5.3 6 6.1 6.2 6.2.1 6.3 6.3.1 6.3.2 6.3.3 6.3.4 6.4 6.4.1 Transformation products of plastics stabilizers 65 Introduction 65 Cyclohexadienones and quinone methides from phenolic antioxidants and UV absorbers 66 Products from hydroperoxide decomposing antioxidants Products from hindered amine stabilizers 74 Products from heat stabilizers for PVC Conclusions 75 72 74 Partition coefficients 79 Thermodynamic fundamentals 79 Equilibrium between different phases in ideal solutions Non-ideal solutions 82 Partition coefficients for systems with polymers Additive molecular properties 87 Estimation of partition coefficients 90 The regular solution theory 90 UNIFAC 94 The retention index system 110 Expected orders of magnitudes for partition coefficients 80 85 118 Models for diffusion in polymers 125 Diffusion in polymers - The classical approach Diffusion in rubbery polymers 128 Diffusion in glassy polymers 136 Diffusion in polymers - The computational approach Molecular dynamics 142 The transition-state approach 148 Conclusions 151 126 141 Prediction of diffusion coefficients in gases, liquids, amorphous solids and plastic materials using an uniform model 159 Introduction 159 Interaction model 161 Model assumptions 162 Prerequisites for diffusion coefficients 164 Critical temperatures of n-alkanes 164 Critical compression factor 165 The entropy of evaporation 166 The reference temperature 167 The diffusion coefficient 168 Diffusion in gases 168 Conrents XI 6.4.2 6.4.3 7 7.1 7.1.1 7.1.2 7.1.3 7.2 7.2.1 7.2.2 7.2.3 7.2.4 7.2.5 7.2.6 7.2.7 7.2.8 7.2.9 7.2.10 7.2.11 8 8.1 8.2 8.2.1 8.2.2 8.3 8.4 8.5 8.6 9 9.1 9.1.1 9.1.2 9.1.3 9.2 9.3 9.3.1 9.3.2 9.3.3 9.3.4 Diffusion coefficients in the critical state Diffusion coefficients in amorphous solids 172 172 Transport equations and their solutions 183 The transport equations 183 The terminology of flow 184 The differential equations of diffusion The general transport equations 187 Solutions of the diffusion equation Steady state 189 Nonsteady state 190 Diffusion in a single phase homogeneous system Diffusion in multi-phase systems 198 Diffusion through a liquid boundary layer 209 Surface evaporation 210 Permeation through homogeneous materials 213 Permeation through a functional barrier 213 Permeation through a laminate 217 Concentration dependence of the diffusion coefficient Diffusion and chemical reaction 218 185 188 190 217 Numerical solutions of the diffusion equation 221 Why numerical solutions? 221 Finite-difference solution by the explicit method von Neumann stability analysis 226 The Crank-Nicholson implicit method 227 Spatially variable diffusion coefficient 230 Boundary conditions 231 One-dimensional diffusion in cylindrical and spherical geometry Multi-dimensional diffusion 235 221 233 Permeation of gases, water vapor and volatile organic compounds 239 Permeation of gases 240 Permeability, diffusion and solubility coefficients Experimental measurement of gas permeability Estimation of gas permeability 254 Permeation of water vapor 260 Permeation of organic vapors 262 Dependence of permeability coefficient on concentration Measurement of partition and diffusion coefficients 271 The significance of partition coefficients The significance of diffusion coefficients 240 250 262 273 282 XI1 Contents 10 Migration of plastic constituents 287 10.1 10.1.1 10.1.2 10.2 10.2.1 10.2.2 10.2.3 10.2.4 10.2.5 10.2.6 10.2.7 10.3 10.3.1 10.3.2 10.3.3 10.3.4 13 11.1 11.2 11.3 11.4 11.5 12 12.1 12.2 12.2.1 12.2.2 12.3 12.3.1 12.3.2 Principles of migration testing 287 Parameters determining migration 288 Migration control methodologies 291 Analysis of specific migrants 300 The positive list system within the European Union Legislation 300 General requirements to analytical methods for compliance testing Establishing (juristically) valid performance of methods 302 A practical guide for developing and pre-validation of analytical methods 306 Availability of (pre)validated methods in Europe 313 Practical examples 317 The concept of functionality of validation procedures and precision data for compliance testing 334 Safety assessment of modern food packaging applications Recycling used packaging plastics into new food packaging 337 Recycled plastics covered by functional barriers 338 Recycling of post-consumer PET for direct food contact 344 Safety aspects related to refillable plastic bottles 349 300 336 Migration from food packaging: Regulatory considerations for estimating exposure 359 Introduction 359 Estimating the exposure to components of food packaging 362 Establishing a threshold policy for regulating food contact materials 364 Evaluating migration from food packaging materials 366 Using migration modeling to estimate exposure to components of food packaging 374 Appendix 11-1 378 Appendix 11-11 380 Appendix 11-111 383 European Community legislation on materials and articles intended to come into contact with food 393 Introduction 393 Harmonization of national regulations 394 Directives applicable to all materials and articles Directives applicable to one category of materials and articles 398 Directive on plastics materials 399 Community list of authorised substances Authorization of new substances 401 396 399 Contents XI11 12.4 12.5 12.6 12.7 12.8 13 13.1 13.2 13.3 13.3.1 13.3.2 13.3.3 13.3.4 13.3.5 13.4 13.5 14 14.1 14.1.1 14.1.2 14.1.3 14.2 14.2.1 14.3 14.3.1 14.3.2 14.3.3 14.3.4 14.3.5 14.3.6 14.4 14.4.1 Directives on the system of checking migration 402 Other complementary Community initiatives 404 Directives concerning individual substances 405 Activities of other institutions connected with the Community Directives 406 Conclusions 406 Sensory problems caused by food and packaging interactions 407 Problems with off-odor compounds 407 Identification of off-odor compounds 409 Case studies 411 Off-odor from styrene-butadiene coatings 41 1 Off-odor from printing 412 Unsaturated carbonyl compounds 413 Off-odors caused by halogenated phenols and anisols 416 Methylmercaptopentane as an interaction product between packaging and food 417 Parameters determining odor and taste Derivation of threshold concentrations of sensory-active compounds 423 419 Case study: styrene monomer migration into dairy products in single serve portion packs 427 Introduction 427 Content of residual styrene monomer in polystyrene containing food contact materials 427 Taste threshold levels for styrene monomer in foods 429 Analytical methods for measuring styrene Case study: styrene taint in coffee creamers and condensed milk packed in portion packs 431 Threshold concentration of styrene in coffee creamers and condensed milk 432 Estimation of styrene migration from PS Mass balance estimation of worst case styrene migration Effect of partitioning on mass balance Time dependent styrene migration 435 Estimation of styrene diffusion coefficient in PS Functional barrier: estimating the time it takes for styrene to travel through a material 438 Estimation of allowable styrene concentration in polymer 438 Estimation of styrene transfer from portion pack into food 439 Estimation of shelf life based on taint development in creamer portion packs 439 431 432 432 433 435 XIV Contents 14.4.2 Selecting appropriate polystyrene packaging materials for specific packaging applications 441 15 Possibilities and limitations of migration modeling 445 15.1 Migration modeling for polyolefins 446 15.1.1 Estimation of diffusion coefficients for regulatory purposes 446 15.1.2 Estimation of migration values 452 15.2 Migration modeling for non-polyolefins 455 15.3 Optimization of modeling 457 15.4 Migration modeling with new polymer-migrant systems 462 15.5 Modeling of migration from multilayer structures 466 Appendices Appendix I Table 1: Diffusion data for low molecular weight organic substances in Polyethylenes (PE). Low Density Polyethylene (LDPE) and Linear Low Density Polyethylene (LLDPE) 470 Table 2: Diffusion data for low molecular weight organic substances in Polyethylenes (PE). Medium and High Density Polyethylenes (MDPE & HDPE) 498 Table 3: Diffusion data for low molecular weight organic substances in various types of Polypropylenes (PP) 511 Appendix I1 Table 1: UNIFAC group volume (Rk)an d surface area (Qk) parameters Table 2: UNIFAC group interaction parameters for prediction of vapour-liquid 531 equilibria at temperatures between 250 and 425 K 539 Appendix IT1 Table 1: Trivalent phosphorus antioxidants Table 2: Major commercial hindered amine stabilizers 566 Table 3: Major commercial hindered phenolic antioxidants 567 565 Index 569