鞋材共混基体用改性PP 选型，难点不在配比表，在相态做没做出来。同样配比两家做出来不一样，根源通常不在料，在配混与成型。这篇把 PP、EVA、POE 的溶解度参数差、三层相容性判据、增容剂与螺杆剪切历史一并讲透，并给出逐级验证顺序。
"配比表都给你了，照着做就行。"
这是做鞋底件的客户说得最直接的一句话。配方单发过来：PP 基料是同一个牌号，EVA 和 POE 的份数也差不多，可两家料做出来是两个东西——一家的支撑片折两下就发白，耐折过不去；另一家的能过，回弹手感也对。
差的不是配比。差的是相态：同样的成分，在螺筒里被剪了多少次、在什么温度下冷下来，决定了它最后长成什么样。
一、工况六维拆解：鞋底件是低温、弯折、摩擦三条线同时在跑
鞋底不是一个件，是一组件。
| 维度 | 鞋底件的实际工况 | 对材料的要求 |
|---|
| 温度 | 下限到 −20~−30℃（北方冬季、冷库）；上限是夏季地面 50-60℃ | 低温不能脆断，是硬线；高温放大蠕变 |
| 载荷 | 弯折疲劳（整鞋耐折以万次计）+ 持续压缩 + 摩擦（每公里上千次接触） | 耐折、抗蠕变、耐磨三条并行 |
| 介质 | 汗液（内里与中插内侧）、雨水、泥水、清洁剂 | 耐汗、耐水、耐清洁剂 |
| 寿命 | 运动鞋常见按 300-800 km 或 1-2 年设计；日常鞋按年计 | 老化后耐折与硬度保持 |
| 外观 | 白色与浅色底件对黄变敏感；配色件对批间色差敏感 | 耐黄变与批间色差 |
| 合规 | 接触皮肤（内里、中插）；童鞋件执行强制性安全规范；气味在密闭鞋盒里被放大 | 皮肤接触、气味、限量物质 |
温度这一维两头都卡你：低温放大耐折，高温放大压缩与蠕变。所以选型第一句话是"这个件最低用到多少度、压在什么地方"，不是问牌号。再按件位分一遍，归属就清楚了：
【大底插片 / 注塑鞋底】耐磨、防滑、挺度 ▸ 缓震诉求低 ▸ 归属 PP 基、橡胶、TPR/TPU
【支撑片 / 鞋跟稳定片】挺度、耐折、抗蠕变 ▸ 缓震诉求低 ▸ 归属 PP 基、TPU、硬质 PU
【鞋头包头】挺度、耐磨、耐折 ▸ 缓震诉求低 ▸ 归属 PP 基、TPU
【中底主体】回弹、缓震、轻 ▸ 缓震诉求高 ▸ 归属 EVA 基、POE 基、PU
改性PP 在鞋材里不是中底的主体，是"非缓震部位"的基体与改性组分。
二、材料路线对比：EVA 基、POE 基与 PU、TPR、橡胶、EVA+PP 共混的分工边界
这一节只做分工陈述，不做"谁更好"的结论。
| 路线 / 材料 | 拿到什么 | 代价 / 边界 | 适合的部位 |
|---|
| EVA 基（含与 EPDM/POE 并用发泡） | 缓震、轻、工艺成熟 | 交联后难回收、长期压缩易塌 | 中底主体 |
| POE 基（POE 为主或 POE/EVA 并用发泡） | 回弹与压缩形变优于 EVA、低温好 | 单价高、挺度低、加工窗口窄 | 中底高回弹区、超轻中底 |
| PP 基（改性PP 共混） | 挺度高、耐磨、密度低、尺寸稳定；回收性明显优于交联 EVA | 缓震差、低温韧性靠增韧补、收缩大、厚壁件易缩痕 | 大底插片、支撑片、鞋跟稳定片、包头、注塑鞋底、中插 |
| PU | 耐磨、可浇注、密度可调 | 耐水解与耐黄变是长期短板、回收难 | 大底、PU 中底 |
| TPR / TPU | 弹性好、可注塑、可回收 | 密度高、成本高；与 PP 相容性差，包胶需界面处理 | 大底、鞋底贴片、包胶件 |
| 橡胶（硫化） | 耐磨最占优、耐折好 | 重、不可回收、能耗高 | 大底高耐磨区 |
| EVA + PP 共混 | 兼顾一定缓震与挺度，回收性优于交联 EVA | 相容性差、相态难控，可能影响发泡均匀性与回弹 | 大底插片、中插、轻质支撑件 |
分法很朴素：缓震是主诉求的走 EVA 基或 POE 基，挺度耐磨是主诉求的走 PP 基，耐磨到极致不计重量的走橡胶，外观质感优先的走 PU 或 TPU。
文字版结论：EVA+PP 共混是真实存在的路线，但不是"把两边的优点加起来"。 拿到的是挺度与成本，付出的是相态控制难度——相容性差会直接体现在相区粗大带来的力学离散，以及发泡均匀性与回弹的波动。
三、★相态与相容性：PP、EVA、POE 为什么天生是两相，怎么把它做成一相
一句话结论：这三种料在热力学上本来就不该混到一起，能不能用，取决于你有没有人为地把界面做出来。
第一层判据是溶解度参数（Hildebrand 口径），其物理意义是内聚能密度的开平方——两种高分子差得越远，界面张力越高。
| 材料 | 极性 / 结构 | 溶解度参数 δ（(cal/cm³)^½ 口径） | 与 PP 的差 | 相容性判断 |
|---|
| PP（等规均聚） | 非极性，饱和 C–C 主链 | 7.4-8.1（不同资料口径略有出入） | — | 基体 |
| PE / POE（乙烯-辛烯） | 非极性，饱和，支链多 | PE 约 7.98；POE 属同一族，δ 接近 PE | 小 | 部分相容，仍是两相 |
| EVA（VA 含量高的牌号） | 含醋酸乙烯链段，极性随 VA 上升 | 9.1-9.5 | 约 1.0-1.4 | 热力学上更不相容 |
| PVC（对照） | 极性 | 约 9.55 | 更大 | 必须增容 |
（δ 值口径：A 级 US4713271 专利说明书 Table I；B 级 公开高分子物性资料。）
这张表容易被误读成"POE 和 PP 能混、EVA 和 PP 不能混"，第二层判据马上就否掉它。
第二层 · 结晶度与结晶温度差。 PP 熔点 160-170℃，POE 结晶区的结晶温度远低于它——熔体冷下来时 PP 先结晶，把还没结晶的弹性体相往外挤。所以哪怕 δ 只差零点几，PP/POE 依然是两相体系。 区别只在：它是"界面张力低的两相"，相区能做小、做稳；PP/EVA 是"界面张力高的两相"，不做增容就又粗又散。
第三层 · 黏度比与剪切。 两相黏度比接近 1 时，分散相最容易被剪切打碎；相差太大就打不碎、或打碎了立刻聚并回去。黏度比由配比决定，打碎与聚并的平衡由剪切历史决定——这就是同一张配比表在两台机器上出来两种结果的原因。
三条控制路线，各管一段。
路线 1 · 增容剂。 PP-g-MAH、POE-g-MAH、接枝弹性体——降低界面张力、稳定相区、改善界面粘结。公开相容剂产品资料的推荐加量是 2-10 wt%、常见接枝率 0.9-1.3 wt%（B 级）；代价是成本上升，过量还可能形成第三相。
路线 2 · 控制配混工艺。 螺杆组合、剪切强度、温度分布、喂料方式、停留时间——把相区尺寸打小并均匀化，也是唯一能"现场改相态"的手段。代价是剪太强会降解断链、剪太弱相区粗大。
路线 3 · 选内聚能密度更接近的牌号组合。 从源头把 δ 差与黏度比放进有利区间，代价是可选牌号受限。
一句口诀压住这一节：δ 差决定要不要增容，黏度比决定能不能打碎，冷却结晶顺序决定相区稳不稳。 三件事只做一件，相态都出不来。
四、★同一个牌号，两家做出来不一样：问题通常不在料
结论先给：同一个牌号、同一张配比表，两家做出来不一样，根源通常不在料，在配混与成型。因为相区尺寸对剪切历史极其敏感。
这条链可以查：
螺杆组合（剪切元件怎么排）→ 熔体承受的剪切与拉伸强度 → 分散相液滴的"打碎—聚并"平衡 → 相区尺寸与分布 → 界面粘结与应力传递 → 落成件的冲击、耐折与回弹
同一条链上，喂料方式、温度分布、停留时间分布各动一环，出口相态就变。所以"换个料就好"在共混体系里经常不成立——你换的可能不是料，是一套未知的相态。
为什么照着配比表复刻经常失败？ 因为配比表给的是成分，不是相态：
给到 ▸ 各组分的质量份、基材牌号，可能还有填料与助剂
没给 ▸ 各组分从哪个位置加进去（喂料顺序、增容剂要不要预混）
没给 ▸ 熔体在螺筒里被剪了多少（比机械能）、停留时间分布与温度分布
没给 ▸ 冷却与保压条件（成型那一段决定相区最后长多大）
配比是成分，相态是历史。 成分相同、历史不同，出来就是两种材料。
敢否定一个常见做法： 遇到"同配比不同结果"，很多人第一反应是"换一个更好的 PP 基料"。这一招在共混体系里经常是反向操作——问题出在相区粗大与分布不均时，换料只是换了一套未知相态，往往第一版对了、第二批又回去。正确第一步是先看相态，再决定调工艺还是调配方。
一个内行细节：判断相态做没做出来，不一定非等测试报告。 低温冲击断口是免费信息——相区分散均匀、界面粘结好的断口是麻面状韧性撕裂；相区粗大或团聚的断口会出现明显镜面区。同一个配比，两家断口形状不一样，基本就说明相态不同。
五、★选型判据表：八项指标，每项都带验证方法
注意第三列"验证方法·标准号"——选型最常卡住的不是"看哪个指标"，而是"拿什么测、测到多少算过"。
| 指标 | 门限值（典型） | 验证方法 · 标准号 | 常见失效 | 通行解法 |
|---|
| 硬度（件级） | 公开专利口径：PP 基鞋底可取 Shore A 65-75 | GB/T 3903.4-2017（外底硬度）；材料级可参照 GB/T 2411（发布前复核） | 件太软支撑不住，太硬折不动 | 调均聚/共聚比例与增韧体系 |
| 弯曲模量（挺度） | 支撑片、包头按件倒推；PP 基体系常见 800-2000 MPa 档（典型值，以 TDS 为准） | GB/T 9341 | 支撑片软塌、稳定片变形 | 矿物填充补刚，或提高均聚比例 |
| 常温耐折 | 按产品标准与客户里程要求；GB/T 3903.1-2017 适用前提是跟高 ≤70 mm、鞋底屈挠部位厚度 ≤25 mm、刚性弯折角 ≥45° | GB/T 3903.1-2017 | 弯折处裂口、发白 | 增韧 + 压制相区粗大 + 结构减薄 |
| 低温耐折 | 按最低使用温度设门限（−20~−30℃ 预处理后耐折） | GB/T 3903.1-2017（预处理参照 GB/T 3903.7-2019） | 冬季弯折脆断 | 增韧体系 + 增容剂提升界面粘结 |
| 耐磨（DIN 磨耗） | 体积磨耗量按件与客户定；鞋类也常参照 ISO 20344 / GB/T 20991 | GB/T 9867-2008（等同 ISO 4649:2002）；GB/T 3903.2-2017 | 大底磨平、花纹消失 | 选耐磨体系；公开专利口径显示加少量硅橡胶可降磨耗量 |
| 耐黄变与气味（白/浅色件） | 耐黄变按客户色卡与灰卡评级；童鞋件执行 GB 30585-2014（异味、甲醛 ≤20 mg/kg、邻苯二甲酸酯 ≤0.1%） | HG/T 3689-2014（方法A）+ GB/T 4841.3-2006 灰卡；GB 30585-2014 异味 | 白色底件发黄、开盒异味 | 抗氧 + 耐候 + 低气味低 VOC 体系 |
| 收缩率与翘曲（厚壁工艺） | PP 收缩率公开工艺口径 0.5%-2.5%，厚壁件取上限 | GB/T 17037.4 / ISO 294-4 | 缩痕、内部气孔、翘曲 | 保压取注射压力的 50%-80%、延长保压、随形冷却 |
文字版结论：GB/T 3903.1-2017 的适用性最该先确认——它明确不适用于跟高大于 70 mm、鞋底屈挠部位厚度大于 25 mm，或刚性弯折角度小于 45° 的整鞋与鞋底。很多厚底与加厚中插件根本不在这个标准的适用范围内，拿它当验收依据，测出来的数不能代表件的耐折。GB/T 3903.2-2017 同样不适用于天然皮革外底与生胶底。
六、常见失效与根因：四个现象，四条根因
失效一：弯折处裂口与发白。 根因分两类——相区粗大导致的界面脱粘（材料侧），与屈挠部位厚度超标或转角应力集中（结构侧）。先量厚度和转角，再谈换料。
失效二：低温一折就断。 根因不是"PP 天生脆"，而是增韧相的相区尺寸与界面粘结没做到位——δ 差没被增容剂压下来时，弹性体相实际上是在当缺陷用。敢否定的是这条：很多人靠"多加点增韧剂"解决低温断裂，方向常常是错的。加量上去，相区更容易聚并变大，冲击可能不升反降，挺度还先掉。正确顺序是先把界面和相区做小，再谈加量。
失效三：厚壁件缩痕与内部气孔。 根因是 PP 结晶收缩快、厚壁处补缩不足。缩痕高发在加强筋根部与壁厚突变处；内部气孔是冷却过快形成的真空孔，公开工艺资料给的量级是直径 0.5-3 mm。对症做法在工艺侧：保压取注射压力的 50%-80%、延长保压、厚壁处降低注射速度、厚壁区加强冷却。这是工艺账，不是配方账。
失效四：白色件黄变与批间色差。 黄变先查抗氧与耐候体系、再查仓储紫外；色差要分两步：先查色母批次，再查相态。 相态变化会改变材料内部的光散射，同一支色母在不同相态下呈现的颜色本来就不一样。
七、验证顺序：先定件与部位，再逐级往下
顺序错了，成本会在最后一步集中爆出来。
| 顺序 | 验证项 | 不过就退回的判据 |
|---|
| ① 定件与部位 | 明确是大底插片、支撑片、包头、鞋跟稳定片还是中插 | 部位没定，挺度与缓震的要求都定不下来 → 退回重定 |
| ② 相态与基础力学 | 断面观察 + 拉伸 / 弯曲 / 缺口冲击 / 硬度，把配比确认成配方 | 相态不均、力学离散度大 → 退回配混工艺与增容体系 |
| ③ 常温与低温耐折 | 常温按 GB/T 3903.1-2017（先确认在其适用范围内）；低温按 −20~−30℃ 预处理后耐折 | 裂口、发白或脆断 → 退回增韧体系与相区控制 |
| ④ 耐磨与硬度 | GB/T 9867-2008、GB/T 3903.2-2017、GB/T 3903.4-2017 | 磨耗超差或硬度跑偏 → 退回基材档与耐磨体系 |
| ⑤ 缩痕与翘曲 | 厚壁工艺窗口：保压、模温、冷却、注射速度 | 缩痕或翘曲超差 → 退回模具与工艺，不是料 |
| ⑥ 耐黄变与气味 | HG/T 3689-2014（方法A）；童鞋件按 GB 30585-2014 测异味 | 超差 → 退回抗氧耐候体系与低气味体系 |
| ⑦ 整鞋耐久 | 实际里程或耐折台架 + 落成件复检 | 现场失效 → 回到 ① 重定部位与工况 |
最常见的错误是跳过 ② 直接上 ③。 相态还没做出来就去比耐折，比出来的其实是那一次试模的临时条件，不是这批材料的性能——这也是"同一批料两次测出两个结论"的常见来源。
八、反向诚实：这三种情况，鞋材共混基体不该硬用改性PP
前面讲"怎么做"，这里讲"什么时候别做"。
| 出现的情况 | 为什么改性PP 基不合适 | 该往哪走 |
|---|
| 要求高回弹缓震（中底主体） | PP 基体系的缓震靠泡孔与弹性相，回弹与压缩形变都拼不过 EVA 或 POE 发泡体系 | 走 EVA 基或 POE 基发泡中底（EVA+POE 并用是行业通行做法） |
| 要求极高回弹与低密度同时成立 | 两者都要靠发泡实现，而 PP 熔体强度低、发泡窗口窄 | 走 POE 基或 POE/EVA 并用发泡体系 |
| 长期高频弯折，且不允许任何硬度漂移 | PP 是半结晶聚合物，结晶度会随使用时间与环境温度缓慢变化 | 走交联弹性体或橡胶类体系，或改到非承力部位 |
| 要求与 TPU 或橡胶大底直接热贴合、包胶 | PP 非极性、表面能低，与极性 TPU 的界面粘结差 | 走增容或底涂路线，或改由 TPR/TPU 承担贴合面 |
规律是一致的：只要出现"缓震是主诉求"，或者"两个方向相反的要求同时要"，就说明这个件不该用 PP 基硬撑。
九、换料要动什么：一张先看再动的清单
决定试改性PP 共混料之前，这张表建议先过一遍。客户真正的顾虑往往不是性能，是"我现在的模具和工艺要不要改"。
| 要动的项 | 需要确认什么 | 不做会怎样 |
|---|
| 配混工艺（若自制共混料） | 螺杆组合、喂料顺序（增容剂是否预混）、温度分布、停留时间 | 相态换了，同一配比出来两个件 |
| 模具收缩率 | 新料收缩率与原方案的差，厚壁件对收缩更敏感 | 尺寸超差、装配对不上 |
| 浇口与排气 | 共混体系的流动差异；厚壁件的排气 | 充填不足、熔接线位置变化、困气烧焦 |
| 料温与模温 | 加工窗口对结晶与相区的影响 | 表面缺陷、缩痕、韧性波动 |
| 干燥 | 填充料与含回料体系需要按体系定 | 银丝、内部气孔 |
| 保压与脱模 | 收缩差异带来的缩痕与顶白 | 缩痕、翘曲、顶出拉伤 |
| 色差 | 相态变化会改变呈色，配色件必须先确认色板再上机 | 批次色差争议 |
换料要动的是配混、模具、工艺、色差四块。下面这张表是把结论直接往上报用的。
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 大底插片 / 注塑鞋底 | 改性PP 基 + 增韧与耐磨体系 | 硬度、DIN 磨耗、常温耐折 | GB/T 3903.4-2017、GB/T 9867-2008、GB/T 3903.1-2017 | 耐磨门限、是否接触地面油污 |
| 支撑片 / 鞋跟稳定片 | 改性PP 基 + 矿物填充补刚 | 弯曲模量、抗蠕变 | GB/T 9341 | 挺度要求、壁厚 |
| 鞋头包头 | 改性PP 基 + 增韧与界面增容 | 低温耐折、硬度 | GB/T 3903.1-2017、GB/T 3903.4-2017 | 最低使用温度 |
| 白色 / 浅色底件 | 耐候抗黄变 + 低气味体系 | 耐黄变、气味 | HG/T 3689-2014（方法A）、GB 30585-2014 | 色卡与灰卡要求 |
| PP 混入现成 EVA 体系 | 先做增容体系与相态验证，再谈比例 | 相区尺寸、发泡均匀性、回弹 | 断面观察 + 上列表 | 现有配混设备能否调螺杆组合 |
文字版结论：判断标准只有一条——客户拿这两张表，能不能在一次会议里把材料方向定下来。 定不下来，通常是"件位"和"最低使用温度"这两个输入还没给。
十、这个件上最容易出问题的，往往不是料
鞋底件上最常见的两类投诉是"冬天一折就断"和"同一张配比表两家做出来不一样"，这两类问题里由材料本身引起的比例并不高。前者的判据标准里写得清楚：耐折按 GB/T 3903.1-2017、耐磨按 GB/T 3903.2-2017 或 GB/T 9867-2008 做，且 GB/T 3903.1-2017 对跟高、屈挠部位厚度与刚性弯折角都有适用前提；后者基本能从相态与配混工艺上找到答案——同一张配比表只给了成分，没给相态。
行业通行的做法是把三件事一起定：基材档位、增韧与弹性体体系（POE、EVA 或并用）、界面增容与相态控制（增容剂加量 + 螺杆组合与温度分布）。三者的配平关系才是这类件真正的技术难点。公开专利口径也印证了这一点：PP 基鞋底材料靠均聚与软质共聚的比例配平拿到目标 Shore A 硬度区间，再靠少量马来酸酐接枝弹性体改界面、少量硅橡胶降磨耗量，缺一个，硬度、防滑或耐磨就有一项掉出去。
宁波市科隆新材料有限公司在这个件上常供的是改性聚丙烯（PP）粒子里的增韧与共混改性方向，按件的部位、最低使用温度与成型方式给到对应的基材档位与增容体系，主要解决上面说的"同配比不同结果与低温耐折"两件事；配方按工况调，相态这一层可以在小试阶段就用断面观察与力学离散度一起确认，件级客户多品种小批量的需求也能接。
常见问答
问：同一张配比表，为什么两家做出来不一样？ 答：配比表给的是成分，相态是另一回事。相区尺寸对剪切历史极其敏感——螺杆组合、喂料顺序、温度分布、停留时间、冷却与保压，任意一项不同，相态就不同。这不是料的问题，也不一定能靠换料解决。
问：低温耐折过不去，多加增韧剂行不行？ 答：方向常常是错的。加量上去相区更容易聚并变大，冲击可能不升反降，挺度还先掉。正确顺序是先把界面和相区做小，再谈加量。
问：PP 混合 EVA 体系，能不能兼得挺度和回弹？ 答：能拿一部分，但要付代价。两者的溶解度参数差在 1 个单位以上，界面要靠增容剂做；PP 相还会挤占体系的连续相空间，可能影响发泡均匀性与回弹。这条路线是"给 EVA 体系补挺度与回收性"，不是"把两边优点加起来"。
最后说两句。 一是配比是成分，相态是历史；二是改性PP 在鞋材里不是中底主体——大底插片、支撑片、包头、鞋跟稳定片、中插才是它该在的地方。
关于我们
同一个牌号，两家做出来不一样，问题出在哪？
料是同一个料，工艺是两套工艺。干燥、模温、螺杆、浇口位置，任意一项偏了，出来就是两个件。选料选对了只算赢了一半。
宁波市科隆新材料有限公司，自产改性聚丙烯（PP）造粒，覆盖均聚 / 无规共聚 / 抗冲共聚三档基材，以及填充、玻纤增强、增韧、阻燃、低气味低 VOC、耐候、免喷涂耐划伤等改性方向；兼营各大石化厂 PP 树脂、副牌料与大包料。配方可调、可配合打样共研、小批量多牌号也能接。
The selection of modified PP for the blended matrix of shoe materials is not difficult because of the formulation table, but rather whether the phase morphology has been achieved. Even with the same formulation, two manufacturers may get different results, and the root cause usually lies not in the materials but in blending and molding. This article thoroughly explains the differences in solubility parameters of PP, EVA, and POE, the criteria for three-phase compatibility, the role of compatibilizers, and the history of screw shear, and also provides a step-by-step verification sequence.
The proportion table has been given to you, just follow it.
This is the most straightforward thing said by a customer who makes shoe soles. The formula was sent over: the PP base material is the same grade, and the amounts of EVA and POE are also similar, but the two suppliers' materials produce two different results—one supplier's support sheet turns white after being bent twice and fails the flex test; the other supplier's passes, and the rebound feel is also correct.
It's not the formulation that's lacking. It's the phase state: the same components, being sheared a certain number of times in the barrel and cooled at a certain temperature, determine how it will ultimately develop.
1. Six-dimensional analysis of operating conditions: The sole component is simultaneously undergoing low temperature, bending, and friction.
The sole is not a single piece; it is an assembly.
| Dimension | Actual working conditions of the shoe sole component | Requirements for the materials |
|---|
| Temperature | The lower limit is −20 to −30℃ (northern winter, cold storage); the upper limit is 50-60℃ on the ground in summer | Low temperature cannot cause brittle fracture; it is a hard wire; high temperature amplifies creep. |
| Load | Bending fatigue (whole shoe flexing counted in tens of thousands) Continuous compression Friction (thousands of contacts per kilometer) | Three parallel lines of fold resistance, creep resistance, and wear resistance |
| Medium | Sweat (inside and inner side of the plug), rainwater, muddy water, detergent | Sweat-resistant, water-resistant, detergent-resistant |
| Lifespan | Sneakers are commonly designed for 300-800 km or 1-2 years; daily shoes are calculated by year. | Flex resistance and hardness retention after aging |
| Appearance | White and light-colored base materials are sensitive to yellowing; colored parts are sensitive to batch-to-batch color differences | Yellowing resistance and batch-to-batch color difference |
| Compliance | Contact with skin (inner lining, midsole); children's shoes comply with mandatory safety standards; odors are amplified inside a sealed shoe box | Skin contact, odor, restricted substances |
Temperature is a dimension that restricts you at both ends: low temperatures amplify bending resistance, while high temperatures amplify compression and creep. So the first question when selecting a part is 'What is the lowest temperature this part will experience, and where will it be under pressure,' not asking about the material grade. Then, sort it according to the part's position, and its classification becomes clear:
[Outsole Insert / Injection Molded Sole] Wear-resistant, non-slip, stiffness ▸ Low cushioning requirements ▸ Belongs to PP-based, rubber, TPR/TPU
[Support shank / Heel stabilizer] Stiffness, fold resistance, creep resistance ▸ Low cushioning requirement ▸ Material: PP-based, TPU, rigid PU
[Toe Cap] Stiffness, wear resistance, fold resistance ▸ Low cushioning demand ▸ Belongs to PP base, TPU
[Midsole Body] Rebound, cushioning, lightweight ▸ High cushioning demand ▸ Based on EVA, POE, PU
Modified PP in footwear materials is not the main component of the midsole; it is the matrix and modified component of the 'non-cushioning areas'.
2. Comparison of Material Routes: Division of Roles Between EVA-Based, POE-Based and PU, TPR, Rubber, EVA-PP Blends
This section only presents the division of labor and does not make any conclusions about 'who is better'.
| Route / Materials | Get what | Cost / Boundary | Suitable part |
|---|
| EVA-based (including foaming in combination with EPDM/POE) | Cushioning, lightweight, mature craftsmanship | Difficult to recover after cross-linking, prone to collapse under long-term compression | Midsole body |
| POE base (foam mainly with POE or combined use of POE/EVA) | Rebound and compressive deformation are better than EVA, good at low temperatures | High unit price, low stiffness, narrow processing window | High-rebound midsole area, ultra-light midsole |
| PP Base (Modified PP Blend) | High stiffness, wear-resistant, low density, dimensionally stable; recyclability is significantly better than cross-linked EVA | Poor cushioning, low-temperature toughness improved by toughening, large shrinkage, thick-walled parts prone to sink marks | Outsole insert, support sheet, heel stabilizing sheet, toe cap, injection-molded sole, midsole insert |
| PU | Wear-resistant, castable, density adjustable | Hydrolysis resistance and yellowing resistance have long been shortcomings and are difficult to recycle | Outsole, PU midsole |
| TPR / TPU | Good elasticity, injection-moldable, recyclable | High density, high cost; poor compatibility with PP, encapsulation requires interface treatment | Outsole, midsole patch, rubber-coated parts |
| Rubber (vulcanized) | Most wear-resistant, good folding resistance | Heavy, non-recyclable, high energy consumption | High wear-resistant area of the outsole |
| EVA PP Blend | Balances certain cushioning and firmness, with recovery better than cross-linked EVA | Poor compatibility and difficult phase control may affect foaming uniformity and rebound. | Outsole inserts, mid inserts, lightweight support components |
The classification is very simple: if cushioning is the main concern, go with EVA-based or POE-based; if firmness and wear resistance are the main concerns, go with PP-based; if ultimate wear resistance without regard to weight is desired, go with rubber; if appearance and texture are prioritized, go with PU or TPU.
Text version conclusion: EVA/PP blending is a real route, but it is not 'simply adding the advantages of both sides.' What you get is stiffness and cost, and what you pay for is the difficulty of phase control — poor compatibility directly manifests in mechanical dispersion caused by coarse phase regions, as well as fluctuations in foam uniformity and rebound.
3. ★Phase Behavior and Compatibility: Why are PP, EVA, and POE naturally two-phase systems, and how can they be made into a single-phase system?
In one sentence: Thermodynamically, these three materials should not be mixed together; whether they can be used depends on whether you artificially create the interface.
The first criterion is the solubility parameter (Hildebrand scale), whose physical meaning is the square root of the cohesive energy density—the greater the difference between two polymers, the higher the interfacial tension.
| Material | Polarity / Structure | Solubility parameter δ ((cal/cm³)^½ caliber) | Difference with PP | Compatibility Assessment |
|---|
| PP (isotactic homopolymer) | Nonpolar, saturated C–C main chain | 7.4-8.1 (slightly different according to different sources) | — | substrate |
| PE / POE (Ethylene-Octene) | Non-polar, saturated, heavily branched | PE is about 7.98; POE belongs to the same group, δ is close to PE | small | Partially compatible, still two phases |
| EVA (grades with high VA content) | Contains vinyl acetate segments, polarity increases with VA | 9.1-9.5 | About 1.0-1.4 | Thermodynamically more incompatible |
| PVC (Control) | Polarity | About 9.55 | Bigger | Capacity must be increased |
(δ value caliber: Grade A US4713271 patent specification Table I; Grade B published polymer physical property data.)
This table is easily misread as 'POE and PP can mix, EVA and PP cannot mix,' but the second-level criterion immediately rejects it.
Layer 2 · Crystallinity and difference in crystallization temperatures. The melting point of PP is 160-170℃, while the crystallization temperature in the crystallization zone of POE is much lower than that — when the melt cools down, PP crystallizes first and pushes the still-uncrystallized elastomer phase outward. So even if δ differs by only a few hundredths, PP/POE is still a two-phase system. The difference is only this: it is a 'low interfacial tension two-phase' system, where the phase regions can be small and stable; PP/EVA is a 'high interfacial tension two-phase' system, which, without compatibilizers, becomes coarse and dispersed.
Layer 3 · Viscosity Ratio and Shear. When the viscosity ratio of the two phases is close to 1, the dispersed phase is most easily broken by shear; if the difference is too large, it either cannot be broken or aggregates immediately after being broken. The viscosity ratio is determined by the formulation, and the balance between breaking and aggregation is determined by the shear history—this is why the same formulation table can yield two different results on two machines.
Three control routes, each managed in one section.
Route 1 · Compatibilizer. PP-g-MAH, POE-g-MAH, grafted elastomers—reduce interfacial tension, stabilize the phase region, and improve interfacial adhesion. The recommended addition amount in publicly available compatibilizer product information is 2-10 wt%, with common grafting rates of 0.9-1.3 wt% (Grade B); the cost is increased, and excessive amounts may also form a third phase.
Route 2 · Control the compounding process. Screw combination, shear strength, temperature distribution, feeding method, residence time — reducing and homogenizing the phase region size is also the only way to 'change the phase on-site.' The trade-off is that too much shear will cause degradation and chain scission, while too little shear will make the phase region coarse.
Route 3 · Choose a combination of grades with cohesive energy density that are closer to each other. From the source, put the δ difference and viscosity ratio into a favorable range, at the cost of limited selectable grades.
One mnemonic to keep this section in mind: the delta difference determines whether to increase capacity, the viscosity ratio determines whether it can be fractured, and the cooling crystallization sequence determines whether the phase region is stable. If you do only one of the three things, the phase state cannot be achieved.
4. ★The same brand, but two manufacturers produce it differently: the problem is usually not with the material
Conclusion first: For the same grade and the same formulation sheet, the results from two different companies are not the same. The root cause is usually not in the material, but in mixing and molding. Because the die area size is extremely sensitive to shear history.
This link can check:
Screw combination (how to arrange the shear elements) → Shear and tensile strength the melt bears → 'Breakup-aggregation' balance of dispersed phase droplets → Size and distribution of phase regions → Interfacial bonding and stress transfer → Impact, flexural resistance, and resilience of the finished product
On the same production line, any change in feeding method, temperature distribution, or residence time distribution will alter the phase at the outlet. So 'just change the material' often doesn't work in a blending system — what you may be changing is not the material itself, but a set of unknown phase states.
Why does following the ratio table often result in failure? Because the ratio table gives the ingredients, not the state:
Provide ▸ the mass fractions of each component, the grade of the base material, and possibly the fillers and additives
It doesn't specify ▸ from which position each component should be added (feeding order, whether the functional filler needs to be pre-mixed)
Not given ▸ How much the melt is sheared in the barrel (compared to mechanical energy), residence time distribution, and temperature distribution
Did not provide ▸ Cooling and holding conditions (the molding stage decides the final size of the crystalline regions)
The ratio is the composition, and the phase state is the history. With the same composition but different history, you end up with two different materials.
Dare to question a common practice: When encountering 'same formulation, different results,' many people's first reaction is to 'switch to a better PP base material.' This move is often counterproductive in a blend system — when the problem lies in coarse and uneven phase distribution, changing the material only swaps one unknown phase state for another, often making the first batch right and the second batch go back to being wrong. The correct first step is to look at the phase state before deciding whether to adjust the process or the formulation.
An insider detail: to judge whether the phase structure has been achieved, it isn't necessarily required to wait for test reports. The fracture from low-temperature impact is free information—fractures with evenly dispersed phase regions and well-bonded interfaces appear as dull, tough tears; fractures from coarse or aggregated phase regions will show obvious mirror-like areas. For the same formulation, if the fracture shapes from two companies are different, it basically indicates that the phase structures are different.
5. ★Selection Criteria Table: Eight indicators, each with a verification method
Pay attention to the third column 'Verification Method · Standard Number' — the part that most often gets stuck during selection is not 'which indicator to look at', but 'what to measure with, and how much counts as passing'.
| Indicator | Threshold Value (Typical) | Verification Method · Standard Number | Common Failures | Common solution |
|---|
| Hardness (component level) | Public patent specification: PP base shoe sole can have a Shore A of 65-75 | GB/T 3903.4-2017 (outsole hardness); material grade can refer to GB/T 2411 (review before publication) | If it's too soft, it can't support; if it's too hard, it won't bend. | Adjustment of homopolymer/ copolymer ratio and toughening system |
| Bending modulus (stiffness) | Support plates and head covers are backwards calculated by piece; PP substrate systems commonly have 800-2000 MPa range (typical values, according to TDS) | GB/T 9341 | The support plate is sagging, and the stabilizing plate is deformed | Mineral-filled reinforcement, or increase the homopolymer ratio |
| Room temperature fold-resistant | According to product standards and customer mileage requirements; GB/T 3903.1-2017 is applicable under the conditions of heel height ≤70 mm, sole flexion thickness ≤25 mm, and rigid bending angle ≥45° | GB/T 3903.1-2017 | Cracks and whitening at the bends | Toughening Suppressing coarse phase regions Thinning structure |
| Low-temperature fold resistance | Set the threshold according to the minimum operating temperature (−20~−30°C, foldable after pre-treatment) | GB/T 3903.1-2017 (Preprocessing refers to GB/T 3903.7-2019) | Brittle fracture in winter | Toughening system Capacity-increasing agent enhances interfacial bonding |
| Wear-resistant (DIN abrasion) | The volume of wear is determined per piece in consultation with the customer; footwear often also refers to ISO 20344 / GB/T 20991. | GB/T 9867-2008 (equivalent to ISO 4649:2002); GB/T 3903.2-2017 | The sole is worn flat, and the pattern has disappeared | Choose a wear-resistant system; public patent specifications indicate that adding a small amount of silicone rubber can reduce wear. |
| Yellowing resistance and odor (white/light-colored parts) | Yellowing resistance is rated according to the customer's color card and gray card; children's shoes are executed according to GB 30585-2014 (odor, formaldehyde ≤20 mg/kg, phthalates ≤0.1%). | HG/T 3689-2014 (Method A) GB/T 4841.3-2006 Gray Card; GB 30585-2014 Odor | White base parts turning yellow, unpleasant odor when opening the package | Antioxidant Weather-resistant Low-odor Low VOC System |
| Shrinkage and Warpage (Thick-Wall Process) | PP shrinkage rate public process specification 0.5%-2.5%, use the upper limit for thick-walled parts | GB/T 17037.4 / ISO 294-4 | Sink marks, internal pores, warping | Hold pressure to take 50%-80% of the injection pressure, extend holding time, conformal cooling |
Textual conclusion: The applicability of GB/T 3903.1-2017 should be confirmed first—it explicitly does not apply to whole shoes and outsoles with a heel height greater than 70 mm, a thickness greater than 25 mm in flexible areas of the sole, or a rigid bending angle less than 45°. Many thick-soled shoes and thickened middle inserts are not within the scope of this standard at all; using it as a basis for acceptance means the measured values cannot represent the shoe's resistance to bending. GB/T 3903.2-2017 likewise does not apply to natural leather outsoles or raw rubber soles.
6. Common Failures and Root Causes: Four Phenomena, Four Root Causes
Failure 1: Cracks and whitening at the bend. The root causes fall into two categories — interfacial delamination caused by coarse regional areas (material side), and excess thickness or stress concentration at the bend (structural side). Measure the thickness and the bend first, then discuss material replacement.
Failure 2: It breaks with just one fold at low temperatures. The root cause is not that the 'PP is naturally brittle,' but that the size of the toughening phase domains and the interface bonding were not done properly—when the δ difference isn't reduced by the toughening agent, the elastomer phase actually acts as a defect. What can be asserted is this: many people try to solve low-temperature cracking by 'adding more toughening agent,' but the approach is often wrong. As you increase the amount, the domains are more prone to coalesce and grow, which may actually decrease impact resistance instead of increasing it, and stiffness drops first. The correct sequence is to first optimize the interface and domain size, and then consider increasing the amount.
Failure 3: Sink marks on thick-walled parts and internal porosity. The root cause is that PP crystallizes and shrinks quickly, and compensation shrinkage is insufficient in thick areas. Sink marks frequently occur at the base of ribs and where wall thickness changes abruptly; internal porosity is vacuum pores formed due to overly rapid cooling, with standard process references indicating diameters of 0.5-3 mm. The symptomatic approach on the process side: hold pressure at 50%-80% of injection pressure, extend holding time, reduce injection speed in thick-walled areas, and enhance cooling in thick sections. This is a process issue, not a formulation issue.
Failure Four: Yellowing of white parts and batch-to-batch color differences. For yellowing, first check the antioxidant and weather resistance systems, then check for warehouse UV exposure; color differences should be investigated in two steps: first check the batch of color masterbatch, then check the phase state. Changes in phase state can alter the light scattering inside the material, and the same color masterbatch will naturally appear differently under different phase states.
7. Verification order: first the fixed parts and positions, then proceed step by step downward
If the order is wrong, the costs will all come out in the final step.
| Order | Verification item | However, just the criteria for rejection |
|---|
| ① Fixed Parts and Positions | Clarify whether it is the outsole insert, support piece, toe cap, heel stabilizing piece, or midsole insert | The location hasn't been determined, and the firmness and cushioning requirements can't be settled → Return for redefinition |
| ② Phase State and Fundamental Mechanics | Cross-sectional observation Tensile / bending / notched impact / hardness, confirm the mixture as the formula | Uneven phase and large mechanical discreteness → revert to the mixing process and capacity expansion system |
| ③ Resistance to bending at normal and low temperatures | At normal temperature according to GB/T 3903.1-2017 (first confirm it is within its applicable scope); at low temperature, test for fold resistance after pre-treatment at −20~−30℃ | Cracking, whitening, or brittle fracture → return to toughening system and phase region control |
| ④ Wear resistance and hardness | GB/T 9867-2008, GB/T 3903.2-2017, GB/T 3903.4-2017 | Excessive wear or hardness deviation → return to substrate specification and wear-resistant system |
| ⑤ Indentations and warping | Thick-wall process window: holding pressure, mold temperature, cooling, injection speed | Wrinkles or warping beyond tolerance → Return to mold and process, not the material |
| ⑥ Resistance to yellowing and odor | HG/T 3689-2014 (Method A); children's shoes are tested for odor according to GB 30585-2014 | Extremely poor → Return the antioxidant weather-resistant system and low-odor system |
| ⑦ Overall Shoe Durability | Actual mileage or fatigue test rig Completion part re-inspection | On-site failure → Return to ① Reset position and operating conditions |
The most common mistake is skipping step ② and going straight to step ③. Comparing fold resistance before the phase state is completed actually measures the temporary conditions of that molding trial, not the performance of this batch of material — this is also a common source of the 'two different conclusions from the same batch of material.'
8. Reverse honesty: In these three situations, the shoe material blended matrix should not be forcibly modified with PP.
Earlier we talked about 'how to do it,' here we talk about 'when not to do it.'
| The situation that occurred | Why is modified PP substrate not suitable? | Which way should I go? |
|---|
| Requires high rebound and shock absorption (midsole main body) | The shock absorption of the PP-based system relies on pores and the elastic phase, but its rebound and compressive deformation cannot compete with EVA or POE foam systems. | Use EVA-based or POE-based foamed midsoles (It is common practice in the industry to use both EVA and POE) |
| Requires both extremely high resilience and low density | Both rely on foaming to achieve, while PP has low melt strength and a narrow foaming window. | Use POE base or POE/EVA with a foam system |
| Long-term high-frequency bending, and no hardness drift is allowed | PP is a semi-crystalline polymer, and its crystallinity slowly changes with usage time and environmental temperature. | Use cross-linked elastomer or rubber systems, or move it to a non-load-bearing location |
| Requires direct heat bonding with TPU or rubber outsole, encapsulated with rubber | PP is non-polar, has low surface energy, and has poor interfacial adhesion with polar TPU | Go with the reinforcement or primer route, or switch to having TPR/TPU handle the bonding surface |
The pattern is consistent: whenever 'shock absorption is the main requirement' appears, or 'requirements in two opposite directions are needed at the same time,' it indicates that this part should not be forced with a PP base.
9. What to touch when changing materials: a checklist to look at before taking action
Before deciding to try modified PP blends, it is recommended to go through this table first. The customer's real concern is often not performance, but 'do I need to change my current molds and processes'.
| Items to move | What needs to be confirmed | What will happen if I don't do it? |
|---|
| Blending process (if making the blend yourself) | Screw combination, feeding sequence (whether the capacity enhancer is premixed), temperature distribution, residence time | The phase has changed, and two pieces came out from the same mix ratio. |
| Mold shrinkage rate | The shrinkage rate of the new material differs from the original plan, and thick-walled parts are more sensitive to shrinkage. | Dimensions are out of tolerance, assembly does not align |
| Gate and Vent | Flow differences in the blend system; venting of thick-walled parts | Insufficient filling, weld line position change, air trap burning |
| Material Temperature and Mold Temperature | The effect of the processing window on crystallization and phase regions | Surface defects, shrink marks, toughness fluctuations |
| Dry | Fillers and systems containing recycled material need to be determined according to the system | Silver filaments, internal pores |
| Pressure Holding and Demolding | Shrinkage differences causing sink marks and flash | Indentation, warping, ejection marks |
| Color difference | Phase changes will alter the color, and the color-matching piece must be confirmed with the color swatch before being put on the machine. | Batch color difference dispute |
Changing the material involves four areas: mixing, molds, process, and color difference. The table below is used to report the conclusions directly.
| Scene | Recommended Route | Key indicators | Verification standard | Conditions that need to be confirmed first |
|---|
| Outsole insert / Injection-molded sole | Modified PP Base Toughening and Wear-Resistant System | Hardness, DIN abrasion, room temperature fold resistance | GB/T 3903.4-2017, GB/T 9867-2008, GB/T 3903.1-2017 | Wear-resistant threshold, whether it contacts ground oil stains |
| Support plate / Heel stabilizing plate | Modified PP Base Mineral Filled Reinforcement | Bending modulus, creep resistance | GB/T 9341 | Stiffness requirements, wall thickness |
| Closed-toe | Modified PP Matrix Toughening and Interface Compatibilization | Low-temperature bend resistance, hardness | GB/T 3903.1-2017, GB/T 3903.4-2017 | Minimum operating temperature |
| White / Light-colored base item | Weather-resistant and anti-yellowing, low-odor system | Yellowing resistance, odor | HG/T 3689-2014 (Method A), GB 30585-2014 | Color chart and gray card requirements |
| PP mixed into the ready-made EVA system | First carry out the capacity expansion system and phase verification, then discuss the ratio. | Cell size, foam uniformity, resilience | Cross-sectional observation Top list | Can the existing mixing equipment adjust the screw combination? |
Text version conclusion: There is only one criterion for judgment—whether the client can use these two tables to finalize the direction of the materials in a single meeting. If it can't be finalized, it is usually because the inputs for 'number of parts' and 'minimum operating temperature' have not yet been provided.
10. The part of this item that is most prone to problems is often not the material.
The two most common complaints about outsoles are 'breaking with a single fold in winter' and 'different results from two companies using the same formulation sheet.' In these two types of issues, the proportion caused by the material itself is not high. The criteria for the former are clearly stated: flex resistance is tested according to GB/T 3903.1-2017, wear resistance according to GB/T 3903.2-2017 or GB/T 9867-2008, and GB/T 3903.1-2017 has prerequisites for heel height, thickness and rigidity of bending areas, and bending angle. The latter can basically be explained by the phase state and mixing process—the same formulation sheet only provides the ingredients, not the phase state.
The common industry practice is to set three things together: the substrate grade, the toughening and elastomer system (POE, EVA, or a combination), and interface compatibilization and phase control (amount of compatibilizer, screw configuration, and temperature distribution). The balancing relationship among these three is the real technical challenge for this type of part. The public patent literature also confirms this: PP-based shoe sole materials achieve the target Shore A hardness range by balancing the ratio of homopolymer to soft copolymer, then use a small amount of maleic anhydride-grafted elastomer to modify the interface, and a small amount of silicone rubber to reduce wear. If any one is missing, one of hardness, slip resistance, or wear resistance will be compromised.
Ningbo Kelon New Materials Co., Ltd. commonly supplies modified polypropylene (PP) particles for this kind of part, focusing on toughening and blend modification. The appropriate grade of base material and filler system are provided according to the part, minimum usage temperature, and molding method, mainly addressing the two issues mentioned above: 'different results with the same ratio and low-temperature bending resistance.' The formulation is adjusted according to operating conditions, and the phase state at this level can be confirmed during the small-scale trial through cross-section observation together with mechanical variability. We can also accommodate the needs of part-level customers for multiple varieties and small batches.
Frequently Asked Questions
Q: Why do two manufacturers produce different results using the same formulation sheet? A: The formulation sheet provides the ingredients; phase state is another matter. The size of the phase region is extremely sensitive to shear history—screw configuration, feeding sequence, temperature distribution, residence time, cooling, and holding pressure. If any of these factors differ, the phase state will be different. This is not a problem with the material, and changing the material may not necessarily solve it.
Q: If low-temperature flexural strength can't pass, can we just add more toughening agent? A: The direction is often wrong. Increasing the amount causes the phase regions to combine and grow larger more easily, which may not increase impact strength but rather decrease it, and stiffness may drop first. The correct sequence is to first reduce the size of the interface and phase regions before talking about adding more.
Q: In a PP/EVA blend system, can it achieve both stiffness and resilience? A: You can get a part of it, but at a cost. The solubility parameters of the two differ by more than one unit, so the interface relies on compatibilizers; the PP phase will also occupy the continuous phase space of the system, which may affect foaming uniformity and resilience. This approach is "adding stiffness and recyclability to the EVA system," not "combining the advantages of both sides."
Finally, a few words. First, the ratio is the composition, and the phase state is the history; second, modified PP is not the main component in shoe materials—it belongs in outsole inserts, support pieces, toe caps, heel stabilizing pieces, and midsole inserts.
About Us
The same brand, but two manufacturers produce it differently. Where does the problem lie?
The material is the same, but there are two sets of processes. Drying, mold temperature, screw, gate position—if any one of these is off, you end up with two different parts. Choosing the right material only counts as half the win.
Ningbo Kelon New Materials Co., Ltd. produces modified polypropylene (PP) granules, covering three types of base materials: homopolymer, random copolymer, and impact copolymer, as well as modifications such as filled, glass fiber reinforced, toughened, flame-retardant, low odor/low VOC, weather-resistant, and scratch-resistant without coating. The company also trades in PP resins, off-spec materials, and bulk materials from major petrochemical manufacturers. Formulations are adjustable, and the company can cooperate on sample development, as well as handle small-batch orders of multiple grades.
